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Nutrition Forum
Focus on Felines
St. Louis, Missouri • September 20–22, 2007
A Supplement to Compendium:
Continuing Education for Veterinarians™
Vol. 30, No. 3(A), March 2008
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Nutrition Forum
Focus on Felines
St. Louis, Missouri • September 20–22, 2007
A Supplement to Compendium:
Continuing Education for Veterinarians™
Vol. 30, No. 3(A), March 2008
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Sponsored by an educational grant from Nestlé Purina PetCare Company.
This information has not been peer reviewed and does not necessarily reflect the opinions of, nor constitute or imply
endorsement or recommendation by, the Publisher, Editorial Board, or Nestlé Purina PetCare Company. Neither the
Publisher nor Nestlé Purina PetCare Company is responsible for any data, opinions, or statements provided herein.
© 2008 Nestlé Purina PetCare Company
All rights reserved.
Printed in the United States of America.
Nestlé Purina PetCare Company, Checkerboard Square, St. Louis, Missouri 63164
Designed and published by Veterinary Learning Systems
780 Township Line Road, Yardley, PA 19067
Cover Images: Radius Images/Jupiterimages, Corbis/Jupiterimages, Masterfile
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CONTENTS
Preface and Dedication..............................................................................................7
Dottie Laflamme
SCIENTIFIC PROGRAM: FOCUS
ON
FELINES
Some Highlights in Elucidating the Peculiar Nutritional Needs of Cats...........................9
Quinton R. Rogers and James G. Morris
Advances in Knowledge about Feline Metabolism ........................................................17
Robert C. Backus
Trace Mineral Requirements in Cats: Challenging How We Define “Requirements” ........25
Andrea J. Fascetti
Is My Cat Fat? ........................................................................................................27
Denise A. Elliott
Adipokines and Their Importance in Obese Cats .........................................................30
M. Anne Hickman
New Technologies for Pharmaceutical and Nutrition Research ......................................35
Marnie L. MacDonald
Is the Aging Feline Kidney a Mortality Antagonist? .....................................................38
Dennis F. Lawler
What Is Different about Chronic Kidney Disease in Cats?............................................41
David J. Polzin
Feline Urolithiasis: Understanding the Shift in Urolith Type.........................................44
Jody P. Lulich and Carl A. Osborne
In Search of the Origins of Feline Hyperthyroidism .....................................................47
Deborah S. Greco
Measures of Disease Activity in Feline Inflammatory Bowel Disease...............................51
Albert E. Jergens
RESEARCH ABSTRACTS: ORAL PRESENTATIONS
Dietary Variables That Predict Glycemic Responses to Whole Foods in Cats....................57
N.J. Cave, J.A. Monro, and J.P. Bridges
Spaying Affects Blood Metabolites and Adipose Tissue Gene Expression in Cats ..............58
K.R. Belsito, B.M. Vester, T. Keel, T.K. Graves, and K.S. Swanson
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CONTENTS
Effects of Spaying on Food Intake, Weight Gain, Body Condition Score, Activity,
and Body Composition in Cats Fed a High-Protein versus Moderate-Protein Diet ...........59
B.M. Vester, K.J. Liu, T. Keel, T.K. Graves, and K.S. Swanson
Higher Protein Consumption during Weight Loss Allows Higher Caloric
Intake for Maintenance of Body Weight in Cats..........................................................60
R.S. Vaconcellos, N.C. Borges, K.N.V. Gonçalves, F.J.A. de Paula, E.B. Malheiros, R.S. Bazolli, and A.C. Carciofi
Effect of a Low-Protein Diet on Gut Morphology in Cats..............................................61
D.G. Thomas, C.E. Ugarte, K.J. Rutherfurd-Markwick, and W.H. Hendriks
Variations in Dietary Fat Affect Lipid Metabolism in Domestic Cats .............................62
M.K. McClure, R.J. Angell, K.E. Bigley, K. Fennell, and J.E. Bauer
Impact of Dietary Trans-Fatty Acid on Serum Insulin and Glucose Concentrations in Cats ...63
P.A. Schenck and S.K. Abood
Sequencing and Characterization of Feline Pancreatic Glucokinase cDNA .....................64
S. Lindbloom, M. LeCluyse, E. Hiskett, and T. Schermerhorn
Effects of Epigallocatechin Gallate Singly and in Combination with Lactoferrin
on Oral Health in Cats............................................................................................65
S. Krammer-Lukas, K. Cramer, U. Wehr, S. Gorissen, and K. Elsbett
RESEARCH ABSTRACTS: POSTER PRESENTATIONS
Effect of Isoflavones, Conjugated Linoleic Acid, and L-Carnitine on
Weight Loss and Oxidative Stress in Overweight Dogs .................................................69
Y. Pan, I. Tavazzi, J.-M. Oberson, L.B. Fay, and W. Kerr
Postfeeding Satiety and Weight Loss of Dogs Fed a Vegetable-Based Fiber Supplement........70
Y. Mitsuhashi, K. Bigley, and J.E. Bauer
Body Condition and scFOS Supplementation Influence Adipose Tissue mRNA Abundance ....71
K.R. Belsito, B.M. Vester, F. Respondek, M. Diez, and K.S. Swanson
All-Trans-Astaxanthin Does Not Protect Canine Osteosarcoma Cells from
Chemotherapeutic or Radiation-Induced Cell Death....................................................72
J.J. Wakshlag, C.B. Balkman, A.M. Struble, S.K. Morgan, and M. Zgola
Absorption Trial of Ginkgo Biloba Extract in Cats.......................................................73
A. Pasquini, G. Cardini, C. Gardana, P. Simonetti, G. Giuliani, G. Re, and G. Lubas
High-Protein Diet Impacts Fecal Microbial Populations in Growing Kittens ...................74
B.L. Dalsing, B.M. Vester, C.J. Apanavicius, D.C. Lubbs, and K.S. Swanson
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CONTENTS
Impact of Sampling Interval on the Variability of Activity Counts Recorded
from the Actical Activity Monitor Worn by Pet Dogs ....................................................75
C. Dow, K.E. Michel, and D.C. Brown
Exercise Heart Rate and Blood Lactate Responses as Indicators of Aerobic Capacity in Dogs .....76
J.C. Bouthegourd and A.J. Reynolds
Effect of Different Dietary Protein Sources and Carbohydrate Content on Canine Behavior.....77
O. Pellegrini, L. Casini, V. Mariotti, G. Lubas, and D. Gatta
Evaluation of Polymeric Diets Delivered Directly into the Small Intestine
through Surgically Placed Jejunostomy Tubes..............................................................78
S.A. Bone, F.A. Mann, R.C. Backus, and E. Kelmer
Seasonal Differences in Hair Growth between Long-Haired and Short-Haired Cats ........79
M. Hekman, D.G. Thomas, S.H. Moon, and W.H. Hendriks
Heritability of Hematology and Clinical Chemistry Variables in Domestic Cats:
What Are the Early Implications? .............................................................................80
D.F. Lawler, K. Chase, R. Teckenbrock, and K.G. Lark
Thyroid Hormone Concentrations and Prevalence of Thyroid Pathology in Geriatric Cats.....81
C. Cupp and W. Kerr
Age-Related Changes in Immune Function in Cats......................................................82
K.J. Rutherfurd-Markwick, M.C. McGrath, R.H. Morton, P.C.H. Morel, and W.H. Hendriks
Effect of Dietary Form on Nutrient Digestibility in Cats and Dogs................................83
K. Weidgraaf, S.M. Rutherfurd, K.A. O’Flaherty, D.G. Thomas, and K.J. Rutherfurd-Markwick
Chemical Composition and In Vitro Crude Protein and Fiber Disappearances
of Corn Coproducts from the Ethanol Industry ...........................................................84
M.R.C. de Godoy, L.L. Bauer, and G.C. Fahey, Jr.
Corn Fiber Effects on Nutrient Digestibility and Fecal Characteristics of Dogs ...............85
M.A. Guevara, L.L. Bauer, C.A. Abbas, K.E. Beery, M.A. Franklin, M.J. Cecava, and G.C. Fahey, Jr.
In Vitro Evaluation of Protein Digestibility of Four Pet Foods.......................................86
F. Bovera, S. Calabrò, S. D’Urso, R. Tudisco, A. Guglielmelli, R. Romano, and M.I. Cutrignelli
Review of Pet Dog Feeding Habits in Spain ................................................................87
V.M. Mariotti, M. Hervera, J. Fatjó, M. Amat, M.D. Baucells, and X. Manteca
Use of a Wireless Multisensor Telemetry Capsule for Monitoring the Canine
Gastrointestinal Tract ..............................................................................................88
W.A. Anderson, W. Kerr, and G. Mohr
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PREFACE AND DEDICATION
Preface and Dedication
The objective of the Nestlé Purina Nutrition Forum is to promote advances in veterinary nutrition related to dogs and
cats. Our goal is to further the creation of new knowledge
through quality research and encourage the sharing of that
knowledge by providing suitable venues and programs to facilitate effective communication with a variety of audiences.
By staying true to these objectives, this annual program has
come to be regarded by many as one of the best meetings on
veterinary nutrition.
This year, we have taken the opportunity provided by the
Nestlé Purina Nutrition Forum to recognize something else
that is often regarded as one of the best: the research duo of
Dr. James G. Morris and Dr. Quinton R. Rogers. While true
long-term collaborations are rare in the world of science, anyone who studies feline nutrition instantly recognizes the
names Morris and Rogers. This duo has spent the better part
of their careers working together, exploring the unique nutritional needs of cats. Outside of the pet food industry, these
two were the first to seriously pursue studies in feline metabolism and nutrition. Beginning in the early 1970s, Dr.
Morris set out to build a world-class program in feline nutrition. He enlisted Dr. Rogers to join him, and the rest, as they
say, is history.
Over the next 30 or so years, significant advances were
made in the field of nutrition. Concurrent with this, Drs.
Morris and Rogers expanded our understanding of feline nutrition. When they began studying this field, little was known
about the needs of cats. For example, when they started exploring the amino acid requirements of cats, neither the essentiality of, nor the quantitative requirement for, specific
amino acids had been determined. Much had been extrapolated from other species, but the unique features of feline metabolism identified by Drs. Morris and Rogers and others
showed that such extrapolation was often not appropriate.
Between the two of them, Drs. Morris and Rogers have
shared the results of their research through hundreds of journal articles and research abstracts. Their research helped define minimum requirements for protein and essential amino
acids, vitamins, and minerals for growing and adult cats, and
they contributed to both the National Research Council and
the Association of American Feed Control Officials nutritional guidelines for cats and dogs. In addition, Drs. Morris
and Rogers played a key role in elucidating the link between
feline dilated cardiomyopathy and taurine.
Now retired, Drs. Morris and Rogers leave a lasting legacy
in the knowledge they built and in the students they trained.
As well stated by a former colleague, the generation to follow
them has giant footsteps to fill.
On behalf of Nestlé Purina PetCare, it is with great pleasure that we dedicate the 2007 Nestlé Purina Nutrition Forum
to Dr. James G. Morris and Dr. Quinton R. Rogers.
Dottie Laflamme, DVM, PhD, DACVN
Nestlé Purina PetCare Research
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Some Highlights in Elucidating the Peculiar
Nutritional Needs of Cats
Quinton R. Rogers, PhD, DACVN, and James G. Morris, PhD, DACVN
Department of Molecular Biosciences, School of Veterinary Medicine,
University of California, Davis, California
Animals were originally classified into groups on the basis of
comparative anatomic and physical traits. Because of
anatomic resemblances, sometimes animals that ate similar
diets were grouped together; however, animals that eat similar diets are often in divergent groups. Therefore, zoological grouping does not reflect diet. More modern systems use
cladistic classification, which arranges organisms by their
order of branching in an evolutionary tree, not by their morphologic similarity. Determination of cladistic relationships
has been greatly facilitated by the application of molecular
techniques.
The two most common companion animals belong to
the order Carnivora in the families Felidae and Canidae. Although the term carnivore (derived from the Latin carne,
which means “flesh,” and vorare, which means “devour”) is
used to denote eating of animal tissue, all animals belonging to Carnivora are not carnivores. Some are herbivores or
omnivores, and a number of strict carnivorous animals belong to families other than Carnivora. A strict carnivorous
diet is high in protein, moderately high in fat, and very low
in carbohydrates. This diet also contains the essential vitamins and minerals (if the skeleton is consumed) and fatty
acids to provide a complete diet. One can debate what constitutes a strict dietary carnivore. Certainly, raptors and carnivorous fish, such as salmonids, belong in this category.
Although cats share many of the same characteristics of
these carnivores, cats can also utilize starch. It would appear
that in the evolution of cats, this facility has been maintained, whereas it either has been lost or did not exist in
raptors and carnivorous fish.
Although we have worked on feline nutrition for many
years, we are still fascinated by the nutritional peculiarities of
cats and how, in contrast to dogs or rats, they have modified
their metabolism. This brief review concentrates on some of
the nutritional peculiarities of cats and the mechanisms by
which these adaptations have occurred.
FOOD INTAKE
The early studies of nutritional requirements of animals were
restrained by lack of purified diets that contained defined
quantities of nutrients. Whereas rats and dogs readily ate purified diets, it was difficult to induce cats to consume them.1
Nevertheless, deficiencies of certain vitamins2–5 and minerals6
were observed and studied in cats before the development or
use of satisfactory purified diets. It was not until the 1950s
that purified diets that supported near-normal growth were
developed.7,8
Another major obstacle during the early studies of feline
nutrition was a lack of control of respiratory and other viral
diseases in colony cats. This situation was especially acute in
studies of kitten postweaning growth. The development of an
effective panleukopenia vaccine decreased morbidity and
mortality associated with this disease, but it was not until specific pathogen-free colonies were developed that controlled
studies could be undertaken.
An additional stumbling block was the often finicky feeding behavior of cats.9 Besides being particularly sensitive to
flavor, cats find the texture of the diet very important.1 Various research groups were able to improve consumption of
purified diets by increasing the water content of the diet using
gelatin or agar or formulating the diet as a mash.7,8 It has been
consistently found in various laboratories that weanling kittens more readily adapt to purified diets than adult cats.
However, we have induced adult cats that were not previously
fed purified diets to accept purified diets by using pelleted or
gel diets and gradually mixing the purified diet with a previously acceptable commercial diet over a period of a week or
more (sometimes it takes several weeks). Even then, some
adult cats will not eat enough of the purified diet to maintain their original weight, whereas others may eventually become overweight. Although proteins are neither selected nor
avoided,10 amino acids, peptides, and nucleotides show positive palatability for cats.11,12
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PROTEIN AND AMINO ACIDS
A key difference between the nutritional needs of cats and
omnivores (e.g., rats, dogs) is the quantitatively higher crude
protein (CP) requirement of cats for maintenance and the
higher requirement for arginine, sulfur amino acids, and aromatic amino acids. Cats also show a greater tolerance for excess CP and several essential amino acids and a lesser
tolerance for glutamic acid than other animals. Other key
qualitative differences between cats and omnivores in relation to protein include cats’ requirement for taurine and
niacin, which can be synthesized by most animals from cysteine and tryptophan, respectively.
Protein Requirement
The requirement of bioavailable CP for adult cats is about 160
g/kg diet, whereas the requirement for dogs is about half as
much (80 g/kg diet) and the requirement for rats is less than
one-third as much (50 g/kg diet).13,14 The high CP requirement
of adult cats is reflected by the quantity of protein in all commercial diets formulated for the maintenance of cats, which
for several decades has generally contained at least 280 to 300 g
CP/kg diet; however, the CP requirement for growing kittens,
rats, and puppies is 180, 150, and 180 g/kg diet, respectively.
For cats, there is a small difference between maintenance and
growth requirements due to a considerably higher CP requirement for maintenance, whereas dogs and rats have a higher CP
requirement for growth component. Puppies have a high CP
requirement for growth but a low CP requirement for maintenance, which is consistent with the growth rates of postweaning kittens, rats, and puppies of about 1.5% to 2%, 5% to 10%,
and 2% to 5% of body weight/day, respectively. Thus, the increased need for CP by growing rats and puppies is due to the
higher rate of growth in these species, which also results in a
higher percentage of the dietary nitrogen being used for protein synthesis than for kittens.
The reason for the high CP requirement of adult cats for
maintenance appears to be the metabolic profile of the nitrogen catabolic enzymes, those moving nitrogen into the liver
for the urea cycle and those involved in synthesizing urea.15,16
These enzymes do not downregulate when cats are given lowprotein diets, as occurs in omnivores and herbivores17; therefore, cats cannot conserve nitrogen to the same extent as these
species. Although some adaptation takes place for some of the
essential amino acid catabolic enzymes in cats,18–20 the
changes are minor (about 0.5- to 2-fold) when compared with
rats (2- to 10-fold). In contrast, although cats do not adapt to
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low-protein diets, cats adapt well to diets containing medium
to high protein. Adaptation is achieved by increasing flow
through enzyme systems, including the urea cycle via substrate
regulation, via allosteric regulation, and by increasing metabolic intermediates (e.g., ornithine in the urea cycle),21,22 all
without the necessity of increasing enzyme activities. This
lower ability of cats to conserve nitrogen results in a higher
urinary obligatory nitrogen loss in adult cats fed a protein-free
diet of 360 mg × kg body weight3/4 × day-1 compared to rats or
dogs at 128 and 210 mg × kg body weight3/4 × day-1, respectively.23 Long-term food deprivation also causes a much higher
urinary nitrogen loss in cats24 than it does in omnivores. This
same lack of downregulation of nitrogen catabolic enzymes
results in the protein-efficiency ratio and net protein utilization for the same proteins being much lower for kittens (about
one-half or less) than for rats,25 which is another measurement that shows lower efficiency of utilization of protein for
kittens than for rats or dogs.
Essential Amino Acids
When we began our work on the amino acid requirement of
cats, neither the essentiality nor the requirement for dietary
amino acids had been determined. We began by showing
which amino acids were essential for the cat. As might be expected, because all animals studied (from single-cell animals
to higher animals) had been shown to require eight amino
acids—leucine, isoleucine, valine, methionine, threonine,
phenylalanine, lysine, and tryptophan—we found these also
essential for cats. Not surprisingly, we also found histidine
and arginine to be essential.26 Most surprising were some of
the clinical signs of the deficiencies that we observed. Arginine deficiency produced the most dramatic effect: When
near-adult cats were food deprived overnight and fed a single
meal of 4 to 11 g of an arginine-free diet, within 2 hours all
cats exhibited emesis and lethargy,27 and shortly thereafter
they also vocalized and exhibited frothing at the mouth,
ataxia, emprosthotonos, and exposed claws. One cat, which
had eaten 8 g of the arginine-free diet, showed bradypnea and
cyanosis and died in apnea. These clinical signs were caused
by severe hyperammonemia resulting from a lack of ornithine, an essential intermediate in the urea cycle, thus shutting down urea synthesis.28 Normally, under these conditions,
ornithine is produced from dietary arginine via liver arginase.
Acute short-term deficiencies of any one essential amino acid
for a week or less (except arginine) resulted in no overt clinical signs except a gradual decrease in food intake and weight
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SOME HIGHLIGHTS IN ELUCIDATING THE PECULIAR NUTRITIONAL NEEDS OF CATS
loss.26 During the second week of feeding a diet mildly deficient in threonine (4 g/kg diet), neurologic signs appeared,
including slight tremor, jerky head and leg movements, a stiff
rear gait, difficulty maintaining equilibrium, and weakness
in the front wrist joints such that upon standing, the cats appeared bowlegged. These clinical signs seemed to be of cerebellar dysfunction and all disappeared after supplementation
with adequate threonine (6 g/kg diet).29
Severe histidine deficiency for 1 month resulted in crusty exudates around the eyes and nostrils, whereas an even more prolonged subclinical deficiency (2 to 2.5 g histidine/kg diet, which
supported maximal nitrogen retention) for 4 to 5 months resulted in the development of cataracts in some of the kittens.30
Examination of the eyes revealed changes in the outer fibers of
the lens with no abnormalities seen in the retina.
It was common for dried secretions to accumulate around
the eyes, nose, or mouth of kittens after prolonged ingestion
of diets deficient in essential amino acids. For example, prolonged ingestion of an isoleucine-deficient diet (6 to 7 weeks
at 2 to 4 g isoleucine/kg diet) results in crusty exudate
around the eyes of kittens. Apparently, this condition is due
to infection by common dermal staphylococcal species,
which indicates that isoleucine deficiency impairs the normal resistance to these dermal microorganisms.31 The infections resolved after isoleucine supplementation without
antibiotic treatment.
Another example is the dermal lesions seen around the
mouth and paws resulting from a methionine-deficient diet.32
These lesions are intensified by excess dietary cystine33 and
are similar to those seen under similar dietary treatment of
poults34 and dogs.35 These lesions quickly disappear when
sufficient methionine is added to the diet.
Methionine is of special interest in feline nutrition because
there are unusual pathways in its metabolism. Very little taurine
is synthesized in cats, whereas both isovalthine and felinine,
branched-chain sulfur amino acids are found in cat urine. More
work has been done on felinine, which is considered to be primarily for territorial marking. Felinine is highly odorous and is
the precursor to other highly odorous sulfur compounds that
are products of the decomposition of felinine.36–38 It is now
known that felinine is synthesized from cysteine39 in the liver by
an S-transferase to γ-glutamylfelinylglycine40 with the use of glutathione as a substrate. γ-Glutamylfelinylglycine is transported to
the kidney, where it is hydrolyzed to release felinylglycine and
free felinine, which are excreted in the urine. Testosterone is
known to enhance the synthesis and excretion of felinine.41,42
Amino Acid Intolerances
Other interesting differences in amino acid nutrition between
cats and omnivores, such as the rat and chick, are the lower
tolerances for glutamic acid and the higher tolerances for
most of the essential amino acids except methionine. The
upper limit for dietary glutamic acid for the kitten is about
5% to 6% of the energy.43 When more than 7% of energy
from glutamic acid was given to kittens, occasional emesis
occurred, and kittens given only their normal requirement of
thiamine (4.4 mg thiamine/kg diet) also became thiamine
deficient. With higher dietary thiamine or lower glutamic
acid, the kittens grew normally and exhibited no observable
clinical signs. Rats and chicks tolerate more than twice these
concentrations of glutamic acid. Among the essential amino
acids, the lowest tolerance is for methionine, which is about
1.5% of energy.18,44 An example of higher tolerance is that of
the branched-chain amino acids. A leucine–isoleucine and
valine antagonism could not be shown in kittens unless
isoleucine was limiting, and even then it was mild and transitory.45 Kittens tolerated 10% leucine without a depression in
food intake or weight gain. Also, kittens chose the highleucine diet even when isoleucine was limiting.46
The phenylalanine plus tyrosine requirement of cats is interesting in that only about a 7 g/kg diet is required for maximal growth,47 yet even in adult animals, at least twice this
amount is required to produce enough eumelanin in black
hair to maximize the black color.48
All of these differences in the nutrition and metabolism of
cats versus omnivores can be explained on the basis of cats
being strict carnivores and having evolved to eating small prey
that is medium in fat and high in protein that contains less
glutamic acid than that found in cereal proteins. The low tolerance of methionine that we have found in kittens fed purified
diets may seem to contradict this evolutionary explanation;
however, a diet of meat containing 65% of the energy from
protein and 35% of the energy from fat and carbohydrates (assuming a bioavailability of sulfur amino acids of 85%) would
provide the amount of energy right at this upper limit. It is
known that cats eating high-protein, low-carbohydrate diets
seldom, if ever, become obese. Perhaps it is the methionine
tolerance that limits food intake in these animals.
Taurine
In 1975, Hayes and coworkers49 reported that feline central retinal degeneration is caused by taurine deficiency. Another highlight involving taurine in the nutrition of cats is the recognition
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in 1987 that taurine deficiency also results in dilated cardiomyopathy.50 Between these dates, other clinical signs of taurine deficiency were described, including reproductive and
developmental problems and neurologic, osmoregulatory, and
immunologic defects.51,52 The puzzling part of the finding of
dilated cardiomyopathy in cats was that the cats were normally
eating diets containing 1,200 to 1,400 mg taurine/kg dry matter when the requirement had been determined, using purified diets, to be 400 mg/kg.53 After much research, it was found
that the cause of the higher requirement was the lower digestibility of protein or Maillard reaction products when most
commercial diets (especially canned diets) were fed. These
diets resulted in bacterial conjugated bile acid hydrolase54 activity in the ileum sufficient to cause the hydrolysis of taurocholic acid and the further destruction of taurine, thus
interfering with the enterohepatic reutilization of taurocholic
acid.55–59 Thus, it was not a problem of bioavailability in the
sense of absorption of dietary taurine but in the efficiency of reutilization of taurocholic acid. This was supported by the use
of dietary antibiotics, which resulted in a restoration of taurine
homeostasis in cats given such a diet.54 Thus, there is no single
requirement of taurine for cats but instead a variable requirement between 300 and 2,000 mg/kg diet, depending on the
composition and nature of the diet and its processing.
CARBOHYDRATE UTILIZATION
Because a diet of animal tissue contains only low concentrations of carbohydrate (primarily glycogen), a question arises
whether cats have the ability to utilize plant carbohydrates.
Digestion studies on cats show that starch disappears from the
gut and may be more highly digested by cats than dogs, even
when uncooked.60,61 About four isoenzymes occur in mammalian liver that catalyze the formation of glucose-6phosphate from glucose. The major hexokinase in most
animals is hexokinase D or type IV, often referred to as glucokinase. Glucokinase is absent in the liver of cats,62–64 which
is consistent with the low glucose loads cats experience from
an all-animal tissue diet. Glucokinase is also absent from cat
leukocytes but is present in dog leukocytes.65 Using molecular
techniques, Hiskett et al66 found that the expression pattern
of glucose-sensing proteins in feline liver differed from dogs,
humans, and rodents but that pancreatic expression of these
proteins in cats and other species was similar.
The absence of glucokinase in the liver of cats limits cats’
ability to handle high-glucose loads but does not pose a potential problem unless cats ingest a high-carbohydrate diet,
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such as may come from a non–all-animal-tissue diet. Even
then, the normal eating behavior of cats results in the ingestion
of a number of small meals, which would tend to smooth out
the glucose load. Despite the absence of glucokinase, a number of enzymes related to glucose metabolism (hexokinase,
fructokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, fructose-1, 6-bisphophatase, glucose-6-phosphatase)
are higher in feline liver than in canine liver.64
High intakes of sucrose in cats result in fructosemia and
fructosuria.67 This observation indicates that although fructokinase activity in the liver of cats is higher than in dogs,
there is an impediment in the metabolism of fructose beyond
fructose-1-phosphate. Normally, fructose-1-phosphate is catalyzed to dihydroxyacetone and glyceraldehyde by the enzyme fructose-1-phosphate aldolase, of which there are three
isozymes of aldolase: A, B, and C. Aldolase B is expressed exclusively in the liver, kidney, and intestines. Aldolases mediate two other reactions besides the cleavage of fructose-1phosphate: the cleavage of fructose 1,6-diphosphate and condensation of the triose phosphates, glyceraldehyde phosphate, and dihydroxyacetone phosphate to form fructose
1,6-diphosphate. Reduced cleavage of fructose-1-phosphate
leads to its cellular accumulation and inhibition of fructokinase, causing accumulation of free fructose in the blood,
which would explain the fructosuria.
The evidence suggests that aldolase B activity is probably
low in feline liver, but apparently this has not been measured.
In humans, hereditary fructose intolerance is caused by a deficiency of aldolase B,68 which has been identified as being
due to mutations in the aldolase B gene.69,70 More than 25 enzyme-impairing mutations of the aldolase B enzyme have
been identified.71 Therefore, it appears that there is a high
probability that cats have an inactive aldolase B, which impedes the metabolism of fructose.
A consequence of the poor utilization of fructose by cats is
the diarrhea and diuresis that follow ingestion of either aqueous solutions of sucrose or diets containing high amounts of
sucrose. Providing only sucrose-containing solutions to cats
can result in death. Although sucrose improves the physical
texture of purified diets for cats (compared to starch and glucose, which produce more powdery diets), for the above reasons, the amount in the diet should be restricted.
VITAMINS
Although differences in the protein and amino acid metabolism of cats and omnivores may be anticipated from cats’
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high-protein diet, major differences also occur in the vitamin
requirement of cats and other animals. For many years, the vitamin A requirement of cats was set at a high level, principally
because of the initial studies of feline nutrition by Patricia
Scott and coworkers.72 This group found that kittens given casein diets developed retinal degeneration, and she proposed
that retinal degeneration was a consequence of vitamin A deficiency. Subsequent to the discovery of the role of taurine in
production of central retinal degeneration, the preformed vitamin A requirement of cats was shown to be similar to other
mammals; however, it is in the utilization of the vitamin A
precursor carotenoids that cats are different from most other
animals, including dogs. Carotenoids require cleavage to retinal, the aldehyde form of vitamin A, and it has been unequivocally proven that the major, if not the sole, pathway of
beta-carotene cleavage to vitamin A is by oxidative cleavage of
the central ethylenic bond of beta-carotene to yield two molecules of retinal.73 The enzyme undertaking this cleavage is
beta,beta-carotene 15,15′ monooxygenase (previously known
as beta-carotene 15,15′ dioxygenase), a cytosolic enzyme located in the duodenal mucosa and, to some extent, in the liver
of animals undertaking the carotene conversion. Although the
enzyme has been cloned from chickens and humans, to our
knowledge no studies have been done with cats to determine
whether the enzyme is present or, if present, what factors prevent its activity. The eccentric cleavage of beta-carotene resulting in the formation of apocarotenoids does not appear to be
significant and is present only in in vitro systems in the absence of α-tocopherol. Until further information is available,
it appears that the inability of cats to utilize carotenoids as
precursors of vitamin A is due to lack of or very low activity of
beta,beta-carotene 15,15′ monooxygenase in the intestines
and liver.
Vitamin A plays a key role in the development (as retinoic
acid) and maturation of tissues. In all species of animals, including cats, excessive dietary intakes of vitamin A produce
pathologic changes in fetal and adult tissues.74–76 Animals that
obtain their vitamin A from carotenoids have the ability to
protect against excess vitamin A by downregulation of the enzyme that converts carotene to vitamin A. This step does not
occur in cats, as all the vitamin A is absorbed from tissues that
contain retinol and retinyl esters, which could increase the
susceptibility of cats to vitamin A toxicity; however, kittens
and adult cats can tolerate intakes of vitamin A that would induce toxicity in other species.77 The tolerance of cats appears
to stem from a combination of two factors: the cat’s ability to
sequester larger quantities of vitamin A in the liver with no
apparent adverse effect77 and the form of circulating retinoids
in plasma, which is predominantly retinyl stearate rather than
retinol.76,78 In general, carnivores differ from humans, rats, and
pigs, which have predominantly retinol in their plasma combined with retinol-binding protein. Retinyl esters only appear
in plasma when these animals have excessive intakes. The liver
of cats given high vitamin A diets contains concentrations of
vitamin A in excess of those recorded in animals such as polar
bears (another carnivore), an animal often cited as storing
such large quantities of vitamin A in the liver that it is toxic
when eaten by humans and dogs.
Most animals are independent of a dietary source of vitamin D through ultraviolet (UV) activation of 7-dehydrocholesterol in the skin; however, cats and dogs are unable to
synthesize adequate vitamin D even when shaved and subjected to UV radiation.79 Cats and dogs synthesize 7-dehydrocolesterol, which is also a precursor of both vitamin D
and cholesterol, but cat and dog skin contain only low concentrations, compared with animals that can undertake vitamin D synthesis. When cats are given an inhibitor of the
enzyme that converts 7-dehydrocholesterol to cholesterol (7dehydrocholesterol-Δ7-reductase), the concentration of 7-dehydrocholesterol in the skin is elevated, and when cats are
exposed to UV radiation, they synthesize vitamin D and have
adequate concentrations of 25-hydroxyvitamin D in the
plasma. Therefore, the peculiarity of cats in regard to vitamin
D synthesis is high activity of the enzyme that depletes the
precursor pool for synthesis, not that the enzymes of the synthetic pathway are absent.
Most animals are able to supply their needs for nicotinic acid
by the metabolism of tryptophan in excess of that required for
protein synthesis. Depending on the species, the molar yield of
nicotinic acid from tryptophan is variable (about 30 to 40 mol
tryptophan in rats; 60 mol tryptophan in humans). The catabolic pathway of tryptophan to nicotinic acid has an intermediate: α-amino-β-carboxymuconic-ε-semialdehyde, which can
either proceed to nicotinic acid synthesis or be metabolized to
acetyl coenzyme A (acetyl-CoA) and CO2 by the enzyme picolinic carboxylase.80 The activity of picolinic carboxylase is so high
in cats that virtually none of the intermediate is available for
nicotinic acid synthesis but is metabolized to acetyl-CoA and
CO2, which renders niacin a dietary requirement. Therefore, although cats have the necessary pathway for nicotinic acid synthesis, the activity of an enzyme (picolinic carboxylase) is so
high that it diverts the intermediate for synthesis along an al-
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ternate pathway, a situation analogous to the cat’s inability to
synthesize vitamin D. It has been speculated that because animal tissue is a good source of nicotinamides, there was no evolutionary pressure to maintain synthesis, and some of the
intermediates have carcinogenic potential.
No other specific peculiarities in the cat’s vitamin requirement have been identified (with the possible exception of thiamine, which was discussed in the section on amino acids).
Similarly, the propensity of cats to exhibit clinical signs of vitamin E deficiency is more a reflection of the diet than a difference of requirement.
Finally, to our knowledge, the essentiality of dietary inositol
has not been tested in cats. Under specific conditions of high-saturated-fat diets (e.g., coconut oil), inositol is required by female
gerbils to prevent fatty infiltration of the liver and intestines.81
FATS AND ESSENTIAL FATTY ACIDS
Fats play a significant role in the attractiveness of food for
cats, as well as being an important source of energy. Cats exhibit a distinct preference for some animal fats over other fats
(e.g., chicken fat is preferred over beef tallow, which in turn
is preferred over butter fat). The latter ranking may be related
to olfactory and flavor components in these fats or to the reported aversion of cats to short-chain fatty acids.
Cats, like other mammals, require preformed n-3 and n-6
long-chain essential fatty acids in their diet, as they are unable
to introduce double bonds (desaturate) to precursor fatty
acids beyond carbon 9. These long-chain essential fatty acids,
through chain elongation and desaturation, result in families
of highly active metabolic eicosanoids, such as prostaglandins,
prostacyclines, leukotrienes, and thromboxanes.
There is a general consensus that cats, like other animals,
require linoleate (an n-6 fatty acid) in the diet along with n3 fatty acids, but the exact requirement of cats for long-chain
fatty acids has not been well defined. For most animals,
arachidonate (an n-6 fatty acid) is not essential in the diet,
as the metabolic need for arachidonate can be met through
chain elongation and desaturation of linoleate. There is also
a general consensus that cats have a limited capacity to synthesize arachidonate,82,83 which is attributed to low desaturase activity of cat liver.84,85 Pawlosky and colleagues86
demonstrated that cats possess low Δ6-desaturase activity but
are capable of limited synthesis. Arachidonate-free diets permit similar growth rates in kittens and reproductive success
in males when they achieve adulthood as toms given diets
containing arachidonate.87 The essentiality of arachidonate
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Proceedings, 2007 Nestlé Purina Nutrition Forum
in the diet for multiple litters in queens is somewhat equivocal. Limited numbers of litters have been reported in
queens receiving linoleate and no arachidonate in the diet.88
It has been suggested that some of the problems encountered
with purified diets may be due to the balance of n-3 to n-6
fatty acids. In view of the above, the addition of a source of
arachidonate in the diet of breeding queens is prudent.
Among dietary ingredients, animal fat is highly palatable;
however, the cat has an aversion to medium-chain triglycerides.89
MINERALS
Although the quantitative requirement for mineral elements
in the diet vary across mammalian species (often a function of
relative growth rates), there is general concurrence regarding
which elements are essential. Many minerals (e.g., iron, copper, zinc) are often involved at catalytic sites of the enzymes
that occur across species, whereas elements such as sodium
and potassium have common roles in osmoregulation and
calcium and phosphorus have common roles in the skeleton.
Dietary selection based on minerals is relatively rare. Some
notable exceptions are sodium and phosphorus in ruminants
and several minerals by rats. Many herbivores exhibit a preference for sodium salts or sodium salt solutions that presumably have survival value, as most plants do not require
sodium for growth, and hence vegetable material is low in
sodium. In contrast to herbivores, cats show no preference or
aversion to sodium salts. Even when severely depleted of
sodium and given a choice of diets, cats do not correctly
choose a diet containing adequate sodium over a sodium-deficient diet.90 It would appear that as animal tissue always
contains adequate sodium, the redundant neural pathways
required for detection of sodium either did not develop or
have not been maintained in cats. Although the required concentration of calcium in the diet of growing kittens is much
less than that for large breeds of dogs, it is similar to that for
small breeds of dogs.
CONCLUSIONS
This review is intended to update our earlier reviews on nutritional peculiarity of cats82,91,92 and to indicate how modification of the metabolism of cats has resulted in their distinct
nutrient requirement. The high protein requirement of cats
for maintenance is a consequence of the cat’s limited ability
to downregulate aminotransferases of general nitrogen metabolism and the urea cycle enzymes, which is similar to that
observed in other nonfelid carnivores. It is suggested that this
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SOME HIGHLIGHTS IN ELUCIDATING THE PECULIAR NUTRITIONAL NEEDS OF CATS
confers an advantage to cats because they are always prepared
to ingest a high-protein meal.
Four nutrients plus arginine (which is not essential in the
diet of several mammals, including humans) are essential in
the diet of cats. Arginine and taurine synthesis are limited by
low activities of enzymes in the synthetic pathway. The other
three nutrients are vitamins, two of which (vitamin D and
niacin) are required in the diet even though the pathways for
their synthesis are present. For these two vitamins, degradation
of intermediates by high activities of enzymes for alternate
pathways results in no effective synthesis. The third vitamin
(vitamin A) cannot be synthesized from precursor carotenoids
because of an apparent lack of the monooxygenase enzyme required to cleave the carotenoids. Besides requiring the above
nutrients in the diet, cats show greater sensitivity than omnivores to a number of compounds that occur in plants but not
animal tissue. Fructose is an example of a plant carbohydrate
that is poorly utilized, probably due to low activity of the aldolase B enzyme. Other compounds include benzoate,
sulfhydryl compounds from onions, aspirin, and so forth.14
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Advances in Knowledge about Feline Metabolism
Robert C. Backus, DVM, PhD, DACVN
University of Missouri-Columbia, College of Veterinary Medicine, Columbia, Missouri
The high dietary protein requirement of cats is perhaps the
most often cited attribute for classifying cats as carnivores. Although other nutritional peculiarities of cats support a carnivore designation, such as dietary requirements for preformed
vitamin A, arachidonic acid, taurine, and niacin,1 protein requirement seems to receive the most attention. The high protein requirement applies to all stages of life for cats, with the
maintenance requirement most outstanding compared with
other species. The protein requirement to maintain adult cats
is about twice that needed to maintain adult dogs (160 and
80 g protein/kg of diet, respectively).2 An even greater difference in maintenance protein requirement is observed between adult cats and rats.3
The requirement for a nutrient such as protein is the minimum intake or dietary concentration of a nutrient needed for
an “optimal” response. The classically targeted response in kittens is maximal growth, whereas in adults, nitrogen balance or
constant body weight is targeted. As noted more than 10 years
ago by Morris and Rogers,4 these commonly evaluated responses may not be optimal for establishing protein requirement. In the case of the adult maintenance state, nitrogen
balance may be achieved when protein reserves are depleted
and therefore might not be optimal for long-term health.
Greater dietary concentrations or intakes of protein may support a healthier lean mass, optimize immunologic response,
or generally result in freedom from degenerative disease.
Thirty years ago, Rogers et al5 reported findings that indicated the metabolic basis of the high protein requirement of
cats. The investigators determined enzyme activities in the
livers of adult cats when given diets that were high (700 g/kg)
and low (175 g/kg) in protein and when food was withheld
for 5 days. They evaluated enzymes known in rats to be key
for regulating amino acid and nitrogen metabolism, gluconeogenesis, and lipogenesis. In comparing results between
cats and rats, the investigators made several seminal observations. Especially pertinent to the high protein requirement
of cats was that dietary protein concentration and food withholding have, with few exceptions, little effect on urea cycle,
transaminase, and “first-limiting” amino acid catabolic en-
zyme activities. They also found that activities of the enzymes
in cats, irrespective of diet, were maintained at levels similar
to those in rats given intermediate (400 to 500 g/kg) to high
(800 to 900 g/kg) levels of dietary protein. These observations contrasted sharply with wide variations in enzyme activities (as much as 13-fold) observed in rats given similar
dietary treatments. Compared with cats, enzymatic variations
in rats were acutely and intuitively adaptive. The variations
in rats were appropriate for sparing amino acids during food
deprivation and intake of little dietary protein. The investigators concluded that cats cannot sufficiently downregulate
expression of amino acid and amino nitrogen catabolic enzymes to survive on diets that would marginally meet the
protein requirements of omnivores and herbivores.
AMINO ACIDS AND PROTEIN NITROGEN
In a strict sense, cats and other animals do not have a dietary
requirement for protein; they require amino acid nitrogen,
specific amino acids, and carbon skeletons of other amino
acids that dietary protein provides. This can be well appreciated from a review of many nutritional studies of cats conducted by Morris and Rogers4 and others in which crystalline
amino acid mixtures were substituted for dietary protein. Normal growth rate and maintenance of body weight are observed
in these studies (i.e., when amino nitrogen and essential
amino acids are sufficiently abundant and presented in correct
proportions). Specific amino acids needed in the diet of cats,
so-called indispensable or essential amino acids, were identified in studies using crystalline amino acids in place of intact
protein. Two years after postulating a cause for the high protein requirement for cats, Rogers and Morris6 demonstrated
that the 10 amino acids essential for growth in rats were also
essential for growth in kittens. During the following decade,
these and other investigators using crystalline amino acids determined the minimal dietary concentrations of essential
amino acids needed by kittens for optimal growth.
Rogers and Morris6 found that dietary requirements for essential amino acids in kittens were similar to or only moderately greater (14% to 67%) than those in rat pups, with the
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notable exception of taurine.7 The similarity of essential amino
acid requirements between cats and rats indicated to the investigators that the high dietary protein requirement of kittens
relates principally to a high requirement for amino nitrogen,
not essential amino acids that protein provides. This realization was consistent with the 1977 observation that expression
of liver urea cycle enzymes and transaminases in cats are not reduced in response to intake of diets low in protein. It was also
consistent with results of the species comparisons. Differences
between cats and rats in first-limiting amino acid catabolic enzyme activities were much less than differences between the
species in enzyme activities of nitrogen metabolism.
Since it was proposed, limited hepatic enzymatic adaptability as a cause for high dietary protein requirement in cats
generally has been accepted; however, confirming studies
were lacking. In recent years, this issue has received renewed
attention.
Using indirect calorimetry, Russell et al8 evaluated protein
oxidation in cats consuming high (550 g/kg) and moderate
(442 g/kg) levels of dietary protein. The investigators found
that protein oxidation matched protein intake and concluded
that adapting to varying protein concentrations was not a
problem for cats. They also concluded that there must be another explanation for the high protein requirement of cats.
The inconsistency of their conclusions with those posited 25
years earlier appears to reflect different interpretations of
adaptability and the basis of dietary protein requirement.
With respect to adaptability, implicit in the kind of measurements conducted by Rogers et al5 was that cats have a limited
ability to up- and downregulate enzyme mass per unit of liver
mass. Enzyme activities were measured at presumed maximal
velocity conditions, which generally indicate enzyme mass. Although not specifically stated, other means of regulation were
not discounted by Rogers et al.5 As addressed by Rogers and Morris,9 cats should be able to modulate nitrogen metabolism and
amino acid catabolism by changing liver mass and allosteric regulation of rate-controlling enzyme activities. Indeed, when cats
consume high-protein diets, it has been observed that their livers become enlarged.10 Additionally, because of the nature of enzyme kinetics, enzyme activity varies with the availability of
substrate. Enzymes in vivo function at rates much lower than
their maximum, and their activities increase with substrate concentration. This behavior of enzymes, to some extent, should
account for increasing nitrogen and amino acid metabolism
with increasing dietary protein concentration in cats.
Green et al11 reported findings of protein oxidation in cats
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that were given a wider range of dietary protein concentrations
than were given by Russell et al8 (511 to 77 g/kg versus 550 to
442 g/kg). Using indirect calorimetry, they also found that protein oxidation positively varied with dietary protein content;
however, when cats consumed the lowest level of dietary protein, the ratio of protein oxidation to protein intake increased
to above unity. This result indicated that net catabolism of
body protein occurred at the lowest level of dietary protein,
findings consistent with the protein requirement of cats being
greater than those of dogs and rats. Net catabolism of body
protein would not be observed in rats given the lowest level of
dietary protein. The results were also consistent with earlier
findings showing adaptability of protein oxidation in cats;
however, it is important to note that they also supported limited adaptability to tolerate low levels of dietary protein in cats
relative to dogs and rats. Observations of nitrogen balance in
anorectic cats12 and in cats given protein-free diets13 have indicated that cats have a diminished and slow-reacting ability to
conserve body protein relative to many other species. Limited
regulation of nitrogen catabolic enzymes still appears to be a
tenable cause for these observations.
A fixed and moderately high amino acid and nitrogen metabolism would seem detrimental to cats because of their inefficient use of dietary protein and poor conservation of body
protein; however, these attributes are probably inconsequential to an animal ingesting food that does not vary greatly in
protein content, such as in small mammals, reptiles, amphibians, and insects. Morris, Rogers, and others have suggested advantages to carnivores: Though cats naturally ingest
a low-carbohydrate diet, glucose is made readily available for
catching prey by a high rate of gluconeogenesis from amino
acid catabolism. Also, after periods of food deprivation, ammonium produced after ingestion of prey is less likely to
cause toxicity with a moderately high rather than downregulated nitrogen metabolism.
CARBOHYDRATE METABOLISM
Rogers et al5 found that activities of key regulatory gluconeogenic enzymes in cats were greater than those in rats fed
high-protein diets. As with nitrogen-metabolizing enzymes,
they also found that activities of the gluconeogenic enzymes
were affected little by dietary protein concentration or carbohydrate concentration because sucrose and corn starch
were reciprocally substituted for soy protein to vary dietary
protein concentration. These findings were consistent with
amino acid use for glucose production in cats during the fed
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ADVANCES IN KNOWLEDGE ABOUT FELINE METABOLISM
as well as food-deprived state. As the investigators noted, the
all-meat diet of carnivores would contain little carbohydrate;
therefore, use of amino acids for gluconeogenesis over oxidation would favor meeting obligate tissue needs for glucose.
Subsequent studies appear to confirm the lack of adaptability and substantial glucose production in cats as a result
of amino acid catabolism. Cats given a high-protein (630
g/kg), low-carbohydrate (60 g/kg) diet were found to possess
liver glycogen in amounts similar to those in rats given a
high-protein diet14; however, unlike rats, gluconeogenesis in
liver slices of cats given a high-protein diet is not reduced by
food deprivation. Studies on isolated hepatocytes of cats indicate that catabolic pathways for some amino acids, such as
glycine, are uniquely directed more toward gluconeogenesis
than oxidation.15 Such studies also indicate that as dietary
protein concentration is increased, oxidation, not gluconeogenesis, becomes a more likely fate of amino acids in cat
liver.16 A mechanism for this trend was not postulated. Hence,
although maximal activities of the gluconeogenic enzymes
are not observed to change with dietary protein concentration, adaptation in flux of amino acids away from glucose
production in the liver may occur with increasing dietary protein concentration. This trend may prevent overproduction
of glucose and facilitate glycemic regulation in animals consuming high-protein diets.
Concern about a rising prevalence of diabetes mellitus in
cats in recent years has prompted the suggestion that protein
concentration should be increased in feline dry diets even
though the protein content of such diets is greater than that
needed for maintenance of body weight and nitrogen balance.17 The basis of this suggestion seems to be that increasing
dietary protein concentration will necessarily reduce intake of
dietary carbohydrate and that intake of an “unnaturally high”
amount of carbohydrate is detrimental to the “relatively glucose-intolerant” cat. If reduction of glucose load is beneficial,
it is reasonable to consider that increasing dietary protein in
exchange for carbohydrate will increase glucose entry from the
liver, whereas glucose entry from the intestines is decreased. In
humans, between 50 and 80 g of glucose is estimated to be
derived from 100 g of dietary protein.18
Nonetheless, relative to dietary carbohydrate, dietary protein
probably contributes less to glucose entry, and glucose derived
from dietary protein is probably less dependent on insulin for
disposal. Findings of reduced need for exogenous insulin in diabetic cats given a high-protein, low-carbohydrate diet appear
to support this.19 Also, in normal, healthy cats, plasma glucose
and insulin concentrations are lower when meals of high-protein, low-carbohydrate diets are consumed than when low-protein, high-carbohydrate meals are consumed.20,21 This effect
does not seem to be mediated by improvement of glucose disposal, although increased insulin sensitivity or effectiveness of
glucose is promoting its own disposal.22,23
A benefit of increasing dietary protein may be through reduction of risk for obesity. It is clear that obesity is a contributing factor to development of diabetes in cats.24 Recent
findings of Hoenig et al23 indicate that consumption of high
protein results in a greater heat increment in lean cats but not
obese cats. This thermic effect of protein may be beneficial for
obesity prevention by increasing energy expenditure and satiety. Dietary protein appears to be beneficial in obesity management through maintaining or reducing the loss of lean
body mass, where glucose is mostly disposed, and facilitating
loss of body fat, which positively affects insulin sensitivity.25
LIPID METABOLISM
Activities of a few hepatic enzymes of lipogenesis were evaluated in the 1977 report of Rogers et al.5 As with the other enzymes studied, diet had little to no effect on enzyme activities
in this study. This finding, along with findings of undetectable to low activities of malic enzyme and citrate cleavage enzyme, indicated that cats, relative to rats, have a limited
capacity for de novo synthesis of fatty acids in liver. From this,
the investigators inferred that cats have a limited capacity for
lipogenesis in general.
To the author’s knowledge, little has been reported on lipogenesis in cats. In apparent agreement with the suggestion
of Rogers et al,5 Ibrahim et al26 found undetectable fatty acid
synthesis in livers of cats using an in vivo, deuterated waterlabeling method; however, these investigators determined
fatty acid synthesis in cats during weight loss, when substantial synthesis would not be expected. Rogers et al5 acknowledged that fatty acid synthesis may occur in tissues other than
livers of cats. Richard et al27 determined fatty acid synthesis
rates in liver and adipose slices of cats given a diet low in fat
(80 g/kg), adequate in protein (300 g/kg), and presumably
high in carbohydrate. They found that fatty acid synthesis in
the liver preparations from cats was low when either glucose
or acetate was used as substrate. In this way, cats seemed similar to ruminants. A much greater (about 20-fold) rate of fatty
acid synthesis occurred in adipose tissue compared with liver
tissue. Cats had an intermediate rate of adipose lipogenesis
among species, lower than that in dogs but greater than that
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in rats and humans.
Adipose tissue in cats does appear to be capable of substantial fatty acid synthesis under the right conditions. In cats
deficient in lipoprotein lipase (LPL) activity, body tissues
have impaired access to circulating fatty acids and hyperlipidemia results. In these cats, fatty acids in subcutaneous adipose triacylglycerol are enriched in palmitic acid, the most
abundant product of de novo fatty acid synthesis.28 Although
LPL-deficient cats are generally lean, neutering causes accumulation of body fat mass in the cats to the point that overweight to obese body conditions are observed with ad
libitum food intake.29 For this degree of body fat accretion to
have developed, it is believed that an extraordinary fatty acid
synthesis occurred in adipose tissue.
FUTURE DIRECTIONS
The research of Morris and Rogers,30–39 subsequent to their
initial studies on the high protein requirement of cats, has
revealed other unique metabolic and nutritional attributes of
cats and demonstrated the complexity of establishing dietary
protein requirements. For some amino acids, minimal dietary
concentrations needed for optimal growth in cats were found
to be too low for other body functions. For these amino acids,
dietary requirements were based on more sensitive biomarkers than growth, such as prevention of cataracts in the case of
histidine30 and minimizing urinary excretion of orotic acid
in the case of arginine.31 For some amino acids, the dietary
matrix or proportion of nutrients affected requirements. Taurine and lysine requirements were found to vary with dietary
protein quality, quantity, and processing.32,33 Also, optimizing
the coat color of cats was found to vary with absolute and relative amounts of dietary phenylalanine and tyrosine.34 As in
other species, the requirement for methionine was found to
depend on dietary cyst(e)ine concentration,35 phenylalanine
on dietary tyrosine concentration,36 and arginine on dietary
protein concentration.37 Unique to cats were discoveries that
optimal growth is supported by a very wide range, in ratio, of
dietary essential to nonessential amino acids38 and that requirements for many essential amino acids are reduced with
increasing dietary protein content.39 These and other discoveries revealed that some aspects of control of food intake,
palatability, and metabolism of protein and amino acids in
cats cannot be directly extrapolated from other species.
In considering areas of future research, classical methods
for determining protein and amino acid requirements have
been mostly applied to the growth stage of cats. With the ex20
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ception of lysine and sulfur amino acids, the reported amino
acid maintenance requirements of cats are not based on dose
responses to optimize a biomarker of adequacy.2 Maintenance requirements would be better defined with dose–
response studies. Given that obesity is the most common nutritionally induced disease of cats and is associated with diabetes mellitus and immune dysfunction, it seems worthwhile
to investigate whether maintenance protein and amino acid
requirements should be based on minimizing obesity and diabetes risk and optimizing immune function.
For studies aimed at minimizing obesity risk, recently
neutered (orchiectomized or ovariectomized) young cats that
have finished growing are probably good models. Such cats
are representative of a large fraction of privately owned cats
that will become overweight. Before neutering, cats are typically lean even when they are continuously presented with
food. After neutering, an average increase in body weight of
25% to 30% is observed experimentally with continuous
presentation of food.29 Body condition scoring of cats presented to veterinary clinics show that by middle age (~ 7 years
old), more than one-third of neutered cats will be overweight
or obese.40 The effect of neutering is so potent that postneutering weight gain is also observed in feral cats.41 Such cats
expectedly would experience more exercise and less food
abundance than privately owned neutered cats.
An optimal protein:carbohydrate ratio that reduces postneutering weight gain may facilitate owner efforts to prevent
weight gain in their cats. Relative to carbohydrate, dietary protein is reputed to have a greater satiating potency, lower energy utilization efficiency, and, as shown recently in lean cats,
may induce greater thermogenesis23; however, a few factors
would make determination of an optimal protein:carbohydrate ratio difficult. Variation in palatability among test diets
and amino acid composition of protein sources undoubtedly
would be encountered, which in turn may mask an effect of
changing protein:carbohydrate ratio. Burger and Smith42 experienced a similar problem while investigating protein requirement for maintenance. Because their low-protein diet
was not universally accepted, the protein requirement was
based on observations of selected cats. The greater satiating
potency and thermogenesis and lower energy utilization efficiency of protein over carbohydrate might vary with amino
acid composition. In demonstrating that cats accommodate
maximal growth over a wide range of protein and amino acid
concentrations, Taylor et al43 found that adjustments in dietary concentrations of methionine and arginine affected food
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intake. Toxicity effects of high concentrations of the amino
acids were suggested by the investigators.
The protein and amino acid requirements of overweight
and obese cats should perhaps also be evaluated. These cats
constitute a large fraction of privately owned cats, and corrective weight loss is difficult to achieve, even with diets formulated for weight loss. The obese condition is believed to
increase free-radical production.44 Therefore, obese relative to
lean cats may have a greater requirement for sulfur amino acids
(cyst[e]ine, methionine). Cyst(e)ine that is derived directly
from the diet or from methionine provides reducing equivalents to affect redox status and is a rate-limiting substrate for
synthesis of glutathione, a major cellular antioxidant. The
redox status of cells appears to have roles in modulating signal
transduction, gene expression, and apoptosis.45 Also, methionine, which is consumed in cysteine and glutathione synthesis,
is a methylation substrate, and as such has an important role
in epigenic regulation. Recently, hypomethylation of DNA and
associated proteins has been implicated in the cause of cancers and type-2 diabetes,46 diseases for which obesity increases
the risk of their development in cats.47
Dietary enrichment of leucine may also be beneficial in
managing overweight and obese cats. Leucine is not metabolized extensively in the liver like other branched-chain amino
acids; hence, it reaches skeletal muscle in direct proportion to
dietary concentrations. In skeletal muscle, leucine is a regulator of initiation of protein synthesis, a fuel source, and a principal donor of nitrogen for alanine and glutamine produced by
skeletal muscle.48 Additionally, leucine is believed to modulate
insulin signaling and glucose use in skeletal muscle. These
roles of leucine may be especially important in overweight cats
with insulin resistance because skeletal muscle is both a major
determinant of insulin sensitivity and a consumer of glucose.
Obese humans have improved glucose and insulin responses
to meals when dietary protein is substituted with carbohydrate.49 The mechanism of this benefit is presently unknown
but could plausibly involve leucine from dietary protein.
Protein and amino acid requirements of gestation and lactation are based on analyses of diets that support accepted
but arbitrarily defined levels of performance, such as birth
weight, litter size, and lactational period weight loss in
queens and weight gains in kittens.50 Breakpoints indicating
the minimal dietary concentrations for optimal responses
have not been determined. In the context of increasing recognition of nutrient programming and interest in the health of
aged cats, it seems valid to ask whether dietary protein and
amino acid requirements are optimized for longevity of offspring. The protein:carbohydrate ratio in the diet appears to
have an effect on the body composition of queens during lactation. Queens given dry-type diets have less lactational
weight loss than queens given canned diets.50 The higher carbohydrate content of dry relative to canned diets is suggested
to reduce lactational loss through greater insulin-mediated
inhibition of fat mobilization. Changes in glycemia and
abundance of endocrine factors important to regulation of
body composition in dams are believed to affect eventual
body composition and the propensity for development of diabetes in offspring.51 To the author’s knowledge, this relationship and the potential mediating role of dietary
protein:carbohydrate ratio has not been studied in cats.
As surveys of clinically presented cats indicate, the lifespan
of privately owned cats is increasing; as many as one-third to
one-half of such cats are older than 7 years old.25,52 Protein
and amino acid requirements in aging cats may be unique.
With increasing age, maintenance energy requirement in cats
is reported to decrease by some53,54 but not all investigators.55,56
A tendency for protein digestibility to decrease with age is also
observed.53,55 Because animals eat to meet their energy requirements, protein and amino acid intake will decrease with
decreasing energy requirement. The recent findings of taurine
deficiency in dogs exemplify how changing energy requirements may influence amino acid requirements. Dietary sulfur amino acid concentration must be increased in some diets
to prevent taurine deficiency in dogs with low-maintenance
energy requirement.57 Hence, protein and amino acid requirements may be increased in aged cats that consume less
energy than younger cats. Appreciation of this appears to be
the motivation in recent years for slight increases in the protein content of commercial diets for senior cats.
In old cats, incidence of obesity decreases while, as observed by some investigators, loss of lean mass increases.53
The loss of lean mass is presumably from reduction in skeletal muscle, as observed in aging rodents and humans.58 Skeletal muscle loss is believed by some to be the result of reduced
postprandial protein synthesis and increased visceral amino
acid extraction. Loss of muscle mass is a concern to human
health providers because of associated declines in mobility
and health. Stimulation of skeletal muscle protein synthesis
by dispensable (nonessential) and indispensable amino acids
(in particular, leucine) has prompted investigation of the use
of amino acids to reduce age-related muscle loss.59–61 Similar
investigations may be warranted in cats. Study of dietary ma-
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nipulation to reduce the loss of lean mass is not without
precedent in cats. Cupp62 reported that loss of lean mass in
senior (~ 8 to 12 years old) and geriatric (~ >12 years old)
cats can be altered by nutrient compositional changes unrelated to protein changes.
Aging, as with obesity, is associated with increased oxidative stress, impaired glucose tolerance, and diabetes.63 For this
reason, aged cats may benefit from dietary sulfur amino acid
enrichment, which, as described for obesity, might compensate for possible depletion of glutathione. Indeed, low intracellular glutathione concentrations in peripheral blood
mononuclear cells are observed in elderly humans.64 Although several factors are suggested as causal, an inadequate
supply of precursor amino acids could be responsible. Unfortunately, sensitive biomarkers of sulfur amino acid status
have not been identified in cats. This is perhaps a worthwhile
subject of future study.
The growing practice of clinical nutrition continues to foster interest in the use of varying dietary nutrient concentrations and profiles for treatment and prevention of disease.
Metabolism is variably altered, and usage efficiency is variably
decreased in disease states. The research activities of Morris
and Rogers4–7,9 have provided a valuable foundation upon
which to base dietary protein and amino acid manipulations
for disease treatment. For some diseases, deficiencies in
branch-chain amino acids, arginine, methioine, threonine,
histidine, taurine, and normally dispensable amino acids are
suggested65; however, the need for modification of dietary
amino acid profiles is often uncertain because amino acid requirements for a disease condition generally are not known
and markers of amino acid deficiency used in the healthy state
may not apply to the diseased state. Also, if preexisting malnutrition is not encountered, amino acid mobilization due to
metabolic response to disease may be sufficient to meet shortterm tissue needs. A worthwhile first step in assessing adequacy of amino acid profile in diseased cats might be kinetic
measurements of plasma amino acids with parenteral or enteral feeding.66,67 Although difficult to achieve, measurements
of intracellular amino acid concentrations would be of additional value for assessing adequacy.68 Evaluating the effectiveness of manipulating dietary amino acid profiles to correct a
detected imbalance would be a necessary second step.
In recent years, hypothesized benefits of dietary enrichment
in lysine and glutamine for treatment of disease have been investigated in cats. Interpretation of such studies is often complicated by the necessary experimental design choices. The
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benefit of an amino acid depends on the supplementation
mode, timing, and matrix of administration. For example,
symptoms of feline herpesvirus infection are reduced with lysine given alone in oral capsules69 but not when enriched in a
diet.70 Differences in circulating levels of lysine and nutrient
antagonism are suggested to account for the difference in effectiveness.
Glutamine was evaluated in cats using gastric instillation
of a purified diet that contained glutamine and protein in the
form of crystalline amino acids.71 Glutamine administered in
this way was not protective of methotrexate-induced injury
of intestinal epithelium. One might ask if the outcome would
have been different if intact protein, protein-bound glutamine, or parenterally administered glutamine were used. The
latter condition may be important to the outcome because
compared with villus cells, intestinal crypts derive nutrients
more from the intestinal arterial supply than from the
lumen.72 When glutamine is listed as an ingredient in commercial diets, protein-bound glutamine is most likely being
counted because the free amino acid is labile. Tracer studies
on the rate of protein digestion indicate that amino acids in
protein would be absorbed more slowly than crystalline
amino acids.73,74 Hence, exposure time, the degree of intestinal metabolism, and the peak circulating levels of an amino
acid depend on whether it is in free or bound form. These
variables should be considered in amino acid manipulations
intended for clinical applications.
SOME CHALLENGES
Studies on the use of protein and amino acid manipulations
for clinical applications have additional complexities. Perhaps foremost of these is that patient populations are heterogeneous. Because of this, large numbers of patients are
needed to identify inadequacies and evaluate the effects of
manipulations. Another complexity is measuring end points
quantitatively, such as wound healing and immune response.
Making measurements in a clinical setting is often difficult
or, at best, inconvenient and requires an ardent commitment
of investigators.
Nitrogen balance largely has been relied on to estimate feline maintenance requirements for protein and amino acids.
This measurement and many newer isotopic methods are
heavily influenced by whole-body protein synthesis. In addition to being substrates of protein synthesis, dietary amino
acids become energy sources (e.g., glutamine, glutamate, aspartate), precursors of compounds (e.g., creatine, glutathione,
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nitric oxide), and cellular regulators. Optimizing these latter
functions may require greater dietary amino acid concentrations than those needed to achieve nitrogen balance. A worthwhile direction of future research may be identification and
use of biomarkers of amino acid adequacy that are more sensitive measures of amino acid requirement than body protein
turnover. An example of this would be to measure glutathione
levels in the liver as a means to optimize dietary sulfur amino
acid requirement. Using sulfur amino acids for protein synthesis has a higher priority than glutathione synthesis.75 Liver
glutathione content is important because it serves as a reservoir of cysteine that may be used for synthesis of glutathione
and maintenance of redox status in other tissues.
Another challenge is predicting bioavailabilities of amino
acids in diets prepared for cats. Recommended dietary amino
acid concentrations are greater than the minimum amino
acid concentrations used in defining dietary requirement.
This is because the bioavailabilities of amino acids in ingredients are typically less than 100%, and processing has a variable effect of further decreasing bioavailabilities.76 Lysine is
especially susceptible. Heat treatment of good-quality protein in the presence of moisture and reducing sugar has been
shown to reduce lysine bioavailability in cats by more than
40%.33 Bioassays, rather than chemical assays, presently are
more reliable for accurately determining amino acid bioavailabilities. This was recently demonstrated with several feline
diets.77 Unfortunately, routine use of bioassays for the evaluation of diets is cost prohibitive. A major advance in this area
would be the development of simple and rapid laboratory
tests that reliably indicate amino acid bioavailabilities in feline diets and ingredients used in the diets.
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22. Leray V, Siliart B, Dumon H, et al. Protein intake does not affect insulin
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24. Scarlett JM, Donoghue S. Associations between body condition and disease in cats. JAVMA 1998;212(11):1725-1731.
1. MacDonald ML, Rogers QR, Morris JG. Nutrition of the domestic cat, a
mammalian carnivore. Ann Rev Nutr 1984;4:521-562.
2. National Research Council. Nutrient Requirements of Dogs and Cats. Rev
ed. Washington, DC: National Academy Press; 2006.
3. National Research Council. Nutrient Requirements of Laboratory Animals.
4th Rev ed. Washington, DC: National Academy Press; 1995.
4. Morris JG, Rogers QR. Assessment of the nutritional adequacy of pet
foods through the life cycle. J Nutr 1994;124(12):2520-2534.
5. Rogers QR, Morris JG, Freedland RA. Lack of hepatic enzymatic adaptation to low and high levels of dietary protein in the adult cat. Enzyme
1977;22(5):348-356.
6. Rogers QR, Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109(4):718-723.
7. Morris JG, Rogers QR. The metabolic basis for the taurine requirement
of cats. Adv Exp Med Biol 1992;315:33-44.
8. Russell K, Murgatroyd PR, Batt RM. Net protein oxidation is adapted to
dietary protein intake in domestic cats (Felis silvestris catus). J Nutr
2002;132(3):456-460.
25. Laflamme DP. Nutrition for aging cats and dogs and the importance of
body condition. Vet Clin North Am Small Anim Pract 2005;35(3):713-742.
26. Ibrahim WH, Szabo J, Sunvold GD, et al. Effect of dietary protein quality and fatty acid composition on plasma lipoprotein concentrations
and hepatic triglyceride fatty acid synthesis in obese cats undergoing
rapid weight loss. Am J Vet Res 2000;61(5):566-572.
27. Richard MJ, Holck JT, Beitz DC. Lipogenesis in liver and adipose tissue of the
domestic cat (Felis domestica). Comp Biochem Physiol B 1989;93(3):561-564.
28. Veltri BC, Backus RC, Rogers QR, Depeters EJ. Adipose fatty acid composition and rate of incorporation of alpha-linolenic acid differ between normal and lipoprotein lipase-deficient cats. J Nutr 2006;136(12):2980-2986.
29. Kanchuk ML, Backus RC, Calvert CC, et al. Weight gain in gonadectomized normal and lipoprotein lipase-deficient male domestic cats results from increased food intake and not decreased energy expenditure.
J Nutr 2003;133(6):1866-1874.
30. Quam DD, Morris JG, Rogers QR. Histidine requirement of kittens for
growth, haematopoiesis and prevention of cataracts. Br J Nutr
1987;58(3):521-532.
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31. Costello MJ, Morris JG, Rogers QR. Effect of dietary arginine level on
urinary orotate and citrate excretion in growing kittens. J Nutr
1980;110(6):1204-1208.
32. Kim SW, Rogers QR, Morris JG. Maillard reaction products in purified
diets induce taurine depletion in cats which is reversed by antibiotics. J
Nutr 1996;126(1):195-201.
33. Larsen JA, Calvert CC, Rogers QR. Processing of dietary casein decreases
bioavailability of lysine in growing kittens. J Nutr 2002;132(6 suppl
2):1748S-1750S.
34. Anderson PJ, Rogers QR, Morris JG. Cats require more dietary phenylalanine or tyrosine for melanin deposition in hair than for maximal
growth. J Nutr 2002;132(7):2037-2042.
35. Smalley KA, Rogers QR, Morris JG. Methionine requirement of kittens given
amino acid diets containing adequate cystine. Br J Nutr 1983;49(3):411-417.
36. Williams JM, Morris JG, Rogers QR. Phenylalanine requirement of kittens and the sparing effect of tyrosine. J Nutr 1987;117(6):1102-1107.
37. Taylor TP, Morris JG, Kass PH, Rogers QR. Increasing dispensable amino
acid in diets of kittens fed essential amino acids at or below their requirement increases the requirement for arginine. Amino Acids
1997;13(3):257-272.
38. Taylor TP, Morris JG, Kass PH, Rogers QR. Maximal growth occurs at a
broad range of essential amino acids to total nitrogen ratios in kittens.
Amino Acids 1998;15(3):221-234.
39. Strieker MJ, Morris JG, Rogers QR. Increasing dietary crude protein does
not increase the essential amino acid requirements of kittens. J Anim
Physiol Anim Nutr (Berl) 2006;90(7-8):344-353.
40. Donoghue S, Scarlett JM. Diet and feline obesity. J Nutr 1998;128
(suppl 12):2776S-2778S.
41. Scott KC, Levy JK, Gorman SP, Newell SM. Body condition of feral cats
and the effect of neutering. J Appl Anim Welf Sci 2002;5(3):203-213.
42. Burger IH, Smith PM. Amino acid requirement of adult cats. In: Nutrition, Malnutrition, and Dietetics in the Dog and Cat: Proceedings of an International Symposium Held in Hanover, 3- 4 September 1987. Edney ATB,
ed. British Veterinary Association, pp 49-51.
43. Taylor TP, Morris JG, Willits NH, Rogers QR. Optimizing the pattern of
essential amino acids as the sole source of dietary nitrogen supports
near-maximal growth in kittens. J Nutr 1996;126(9):2243-2252.
44. Keaney JF Jr, Larson MG, Vasan RS, et al. Obesity and systemic oxidative
stress: clinical correlates of oxidative stress in the Framingham Study. Arterioscler Thromb Vasc Biol 2003;23(3):434-439.
45. Young VR, Ajami AM. Metabolism 2000: the emperor needs new
clothes. Proc Nutr Soc 2001;60(1):27-44.
46. Waterland RA. Assessing the effects of high methionine intake on DNA
methylation. J Nutr 2006;136(suppl 6):1706S-1710S.
47. Lund EM, Armstrong PJ, Kirk CA, Klausner JS. Prevalence and risk factors for obesity in adult cats from private US veterinary practices. Int J
Appl Res Vet Med 2005;3:88-96.
48. Layman DK, Walker DA. Potential importance of leucine in treatment of
obesity and the metabolic syndrome. J Nutr 2006;136(suppl 1):319S-323S.
49. Farnsworth E, Luscombe ND, Noakes M, et al. Effect of a high-protein,
energy-restricted diet on body composition, glycemic control, and lipid
concentrations in overweight and obese hyperinsulinemic men and
women. Am J Clin Nutr 2003;78(1):31-39.
50. Piechota TR, Rogers QR, Morris JG. Nitrogen requirement of cats during gestation and lactation. Nutr Res 1995;15(10):1540-1546.
51. Ozanne SE, Constancia M. Mechanisms of disease: the developmental
origins of disease and the role of the epigenotype. Nat Clin Pract Endocrinol Metab 2007;3(7):539-546.
52. Gunn-Moore D. Considering older cats. J Small Anim Pract 2006;47(8):
430-431.
53. Pérez-Camargo G. Cat nutrition: what is new in the old? Compend Contin Educ Pract Vet 2004;26(suppl 2A):5-10.
54. Kienzle E, Edtstadtler-Pietsch G, Rudnick R. Retrospective study on the
energy requirements of adult colony cats. J Nutr 2006;136(suppl 7):
1973S-1975S.
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55. Taylor EJ, Adams C, Neville R. Some nutritional aspects of ageing in
dogs and cats. Proc Nutr Soc 1995;54(3):645-656.
56. Harper EJ. Changing perspectives on aging and energy requirements:
aging, body weight and body composition in humans, dogs and cats. J
Nutr 1998;128(suppl 12):2627S-2631S.
57. Ko KS, Backus RC, Berg JR, et al. Differences in taurine synthesis rate
among dogs relate to differences in their maintenance energy requirement. J Nutr 2007;137(5):1171-1175.
58. Roubenoff R. Sarcopenia: effects on body composition and function. J
Gerontol A Biol Sci Med Sci 2003;58(11):1012-1017.
59. Dröge W, Holm E. Role of cysteine and glutathione in HIV infection
and other diseases associated with muscle wasting and immunological
dysfunction. FASEB J 1997;11(13):1077-1089.
60. Katsanos CS, Kobayashi H, Sheffield-Moore M, et al. A high proportion
of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. Am J Physiol
Endocrinol Metab 2006;291(2):E381-E387.
61. Rieu I, Balage M, Sornet C, et al. Increased availability of leucine with
leucine-rich whey proteins improves postprandial muscle protein synthesis in aging rats. Nutrition 2007;23(4):323-331.
62. Cupp CJ. Nutrient blend for prolonged healthy life in ageing cats. Compend Contin Educ Pract Vet 2007;29(suppl 2A):26-29.
63. Fukagawa NK, Galbraith RA. Advancing age and other factors influencing the balance between amino acid requirements and toxicity. J Nutr
2004;134(suppl 6):1569S-1574S.
64. Hernanz A, Fernandez-Vivancos E, Montiel C, et al. Changes in the intracellular homocysteine and glutathione content associated with aging.
Life Sci 2000;67(11):1317-1324.
65. Soeters PB, van de Poll MC, van Gemert WG, Dejong CH. Amino acid adequacy in pathophysiological states. J Nutr 2004;134(suppl 6):1575S-1582S.
66. Bérard MP, Pelletier A, Ollivier JM, et al. Qualitative manipulation of
amino acid supply during total parenteral nutrition in surgical patients.
J Parenter Enteral Nutr 2002;26(2):136-143.
67. Mansoor O, Breuille D, Bechereau F, et al. Effect of an enteral diet supplemented with a specific blend of amino acid on plasma and muscle
protein synthesis in ICU patients. Clin Nutr 2007;26(1):30-40.
68. Fürst P, Stehle P. What are the essential elements needed for the determination of amino acid requirements in humans? J Nutr 2004;134(suppl 6):
1558S-1565S.
69. Stiles J, Townsend WM, Rogers QR, Krohne SG. Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats.
Am J Vet Res 2002;63(1):99-103.
70. Maggs DJ, Sykes JE, Clarke HE, et al. Effects of dietary lysine supplementation in cats with enzootic upper respiratory disease. J Feline Med
Surg 2007;9(2):97-108.
71. Marks SL, Cook AK, Reader R, et al. Effects of glutamine supplementation
of an amino acid-based purified diet on intestinal mucosal integrity in cats
with methotrexate-induced enteritis. Am J Vet Res 1999;60(6): 755-763.
72. Stoll B, Burrin DG. Measuring splanchnic amino acid metabolism in
vivo using stable isotopic tracers. J Anim Sci 2006;84(suppl):E60-E72.
73. Collin-Vidal C, Cayol M, Obled C, et al. Leucine kinetics are different
during feeding with whole protein or oligopeptides. Am J Physiol
1994;267:E907–E914.
74. Dangin M, Boirie Y, Guillet C, Beaufrere B. Influence of the protein digestion rate on protein turnover in young and elderly subjects. J Nutr
2002;132(10):3228S-3233S.
75. Stipanuk MH, Dominy JE Jr, Lee JI, Coloso RM. Mammalian cysteine
metabolism: new insights into regulation of cysteine metabolism. J Nutr
2006;136(suppl 6):1652S-1659S.
76. Hendriks WH, Emmens MM, Trass B, Pluske JR. Heat processing
changes the protein quality of canned cat foods as measured with a rat
bioassay. J Anim Sci 1999;77(3):669-676.
77. Rutherfurd SM, Rutherfurd-Markwick KJ, Moughan PJ. Available (ileal
digestible reactive) lysine in selected pet foods. J Agric Food Chem
2007;55(9):3517-3522.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Trace Mineral Requirements in Cats: Challenging
How We Define “Requirements”
Andrea J. Fascetti, VMD, PhD, DACVIM, DACVN
Department of Molecular Biosciences, School of Veterinary Medicine,
University of California, Davis, California
Despite advances in our knowledge of companion animal nutrition, very little information is available about trace mineral
requirements in cats. Historically, it has been hypothesized
that such requirements are greater during growth than in other
life stages; however, research determining copper and zinc requirements in queens during gestation offers an interesting
opportunity to examine this hypothesis and raises a larger,
overarching question of how we define nutrient requirements.
COPPER
In 1983, Doong et al1 demonstrated that copper is an indispensable trace mineral in cats. On the basis of that study
and copper requirements in rats, the National Research
Council (NRC) proposed a copper requirement of 5 mg of
copper/kg of diet for kittens for growth2; however, while
testing diets in Association of American Feed Control
Officials protocols, Morris and Rogers observed clinical
signs compatible with copper deficiency in kittens born to
queens consuming a number of different commercial diets
with copper contents exceeding this recommendation (J. G.
Morris and Q. R. Rogers, personal communication, 1994).
Clinical signs included neonatal death, premature birth,
hypochromotricia, and collagen abnormalities. These observations were the stimuli for further investigations concerning dietary copper requirements for gestation and
copper metabolism in cats.
In a study using a depletion–repletion design, queens were
fed a copper-deplete purified diet (0.8 mg copper/kg diet) for
4 months and then randomly allocated to one of three dietary
treatment groups receiving copper (supplied as copper sulfate) at 4, 5.8, or 10.8 mg copper/kg diet.3,4 Dietary copper
concentration had a significant effect on the time to conception (P = 0.04). There also was a negative, linear relationship
between dietary copper (x = mg copper/kg diet) and mean
time (y = days) for queens to conceive (y = 43.38 – 2.87x;
R2 = 0.97). Based on these findings, it was concluded that the
NRC recommendations at the time the study was conducted
(5 mg copper/kg diet) were marginal for reproduction in cats
and that at least 5.8 mg copper/kg diet is necessary.
ZINC
Zinc is an essential trace element for all animals and plays a
role in the function of more than 200 known enzymes. The
ubiquitous distribution of zinc among cells and the fact that
it is the most abundant intracellular trace element suggest that
it has a very basic biologic role. Therefore, zinc is especially
important during reproduction and fetal development. While
evaluating the effects of zinc concentrations on reproductive
efficiency in queens consuming copper-deplete and copperreplete purified diets, I observed a significant number of cleft
palates and low birth weights in kittens born to queens consuming diets with low zinc concentrations (<21 mg zinc/kg).5
The amount and form of dietary copper had no influence on
these findings. At the time this experiment was conducted, the
NRC recommended a minimum of 15 mg zinc/kg diet in kittens fed diets containing a low quantity of compounds known
to decrease zinc bioavailability (e.g., phytate, fiber).1 Our findings challenge that recommendation.
A subsequent study was undertaken with the objective of
determining zinc requirements for queens during gestation
(A. J. Fascetti, unpublished data, 2001). Queens were fed purified diets containing 5, 15, 25, or 50 mg zinc (provided as zinc
sulfate)/kg diet. Reproductive performance in the queens consuming the lower zinc diets was extremely poor, and virtually
all kittens were born dead or died within a day of parturition;
in addition, most of the kittens had congenital abnormalities,
such as cleft palates, clubfeet, or curled long bones. Queens
consuming diets with the greater concentrations of zinc had
higher conception rates and more live births, and their offspring had fewer congenital defects. These findings suggest that
the NRC-recommended minimum requirement at the time
(15 mg zinc/kg diet) was not adequate for reproduction.
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CURRENT RECOMMENDATIONS
The NRC provides recommendations for growth, maintenance, and gestation/lactation for many of the required nutrients. Previous guidelines generally listed only a minimum
requirement for each nutrient. Nutrient recommendations
now span minimum requirements or adequate intakes, recommended allowances, and, where possible, safe upper limits. The current NRC-recommended allowance for queens
during gestation and lactation is 8.8 mg copper/kg of diet.6
This is greater than the current recommended allowances for
growing kittens, which are 8.4 mg copper/kg diet following
weaning and 5.0 mg copper/kg diet for maintenance.6 The
current NRC-recommended allowances for zinc in growing
kittens is 75 mg zinc/kg diet following weaning and 74 mg
zinc/kg diet for maintenance.6 These recommended allowances are greater than that for gestation/lactation, which
is 60 mg zinc/kg diet.6 This recommendation for queens during gestation/lactation was based on findings from two studies, one that determined the nitrogen requirements for
gestation/lactation and one that used the factorial calculation
method for determining the zinc requirement for lactating
queens.7,8
CONCLUSION
The examples of copper and zinc requirements in the queen
during gestation serve as interesting foils for the consideration of how nutrient requirements are determined. Traditionally, it has been suggested that growth is the most
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Proceedings, 2007 Nestlé Purina Nutrition Forum
demanding life stage and that by determining the requirements for growth, one may subsequently apply the findings
to other life stages. Certainly, the example of the copper requirement for feline growth versus that for gestation challenges this assumption. Although the story is not as complete
with respect to zinc, this mineral may be more in line with
previous assumptions that the requirements are greater for
growth. Currently, there is spirited debate regarding how nutrient requirements are determined and how recommendations for minimal and adequate intake and recommended
allowances can be made. All can agree, however, that more
information on the basic requirements for each life stage is
necessary to achieve this goal.
REFERENCES
1. Doong G, Keen CL, Rogers QR, et al. Selected features of copper metabolism in the cat. J Nutr 1983;113:1963-1971.
2. National Research Council. Nutrient Requirements of Cats. Washington,
DC: The National Academies Press; 1986.
3. Fascetti AJ, Rogers QR, Morris JG. Dietary copper influences reproductive efficiency in queens. J Nutr 1998;128:2590S-2592S.
4. Fascetti AJ, Rogers QR, Morris JG. Dietary copper influences reproduction in cats. J Nutr 2000;130:1287-1290.
5. Fascetti AJ. Copper Nutriture in Queens: Dietary Modulation of Cuproenzyme Activities and Reproduction [doctoral thesis]. Davis, CA: University
of California, Davis; 2000.
6. National Research Council. Nutrient Requirements of Cats. Washington,
DC: The National Academies Press; 2006.
7. Piechota TR, Rogers QR, Morris JG. Nitrogen requirement of cats during gestation and lactation. Nutr Res 1995;15(10):1535-1546.
8. Kienzle E. Factorial calculation of nutrient requirements in lactating
queens. J Nutr 1998;128:2609S-2614S.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Is My Cat Fat?
Denise A. Elliott, BVSc, PhD, DACVIM, DACVN
Royal Canin USA, St. Charles, Missouri
Obesity is the most prevalent form of malnutrition in veterinary medicine. Surveys suggest that 25% to 30% of cats presented to veterinary clinics are overweight or obese.1 Obesity
is defined as a pathologic condition characterized by an accumulation of fat in excess of that required for optimal body
function. The significance of obesity pertains to its role in the
pathogenesis of a variety of diseases and the ability to exacerbate preexisting disease.2 “Is my cat fat?” is a question that
cat owners ask veterinarians daily. The ability to answer this
question with objective data requires the ability to accurately
measure body fat. Measurement of body fat also facilitates
understanding the response to weight-reduction programs.
Numerous methods exist for the assessment of body composition; however, techniques such as densitometry, total
body potassium measurement, and neutron activation analysis are not readily available. This discussion will focus on clinically relevant methods, such as body weight measurement,
body condition scoring, morphometric measurements, dilutional techniques, bioelectrical impedance analysis (BIA),
and dual-energy x-ray absorptiometry (DEXA).
Body weight can be subdivided into two or more physiologically distinct components. The traditional two-compartment model divides body weight into fat mass (FM) and
fat-free mass (FFM).3,4 This model forms the basis of the majority of our current knowledge of body composition and depends on assumptions regarding the character of FM and
FFM. The composition of FFM is assumed to be relatively
constant, with a density of 1.1 g/mL at 37°C, a water content
of 72% to 74%, and a potassium content of 50 to 70
mmol/kg.5 In addition, the major constituents of FFM are
presumed to be present in fixed ratios. In comparison, FM is
relatively homogenous in composition, anhydrous, and
potassium free, with a density of 0.900 g/mL at 37°C.
The assessment of body composition in the form of FM
and FFM provides valuable information about the physical
and metabolic status of the individual. FM can be considered
to represent a calorie or energy storage depot, whereas FFM
represents the actual health of the animal. FFM is a heterogenous entity consisting predominantly of intracellular
fluid (ICF) and extracellular fluid (ECF), minerals, glycogen,
and protein. FFM contains body cell mass (BCM), which is
the metabolically active part of the body responsible for determining most of the resting energy expenditure. BCM encompasses those lean tissues most likely to be affected by
nutrition or disease over relatively short periods. Furthermore, FFM is generally accepted as an index of protein nutrition, and therefore changes in FFM over time are assumed to
represent alterations in protein balance.
BODY WEIGHT MEASUREMENT
Body weight measurement is the simplest technique, and it
should be included in the examination of every cat. It provides a rough measure of total-body energy stores and changes
in weight-parallel energy and protein balance. In healthy cats,
body weight varies little from day to day. There can be wide
variations between scales, however. To avoid interscale variation, the same scale should be used each time for an individual cat. In addition, it is preferable to use a pediatric scale and
to routinely calibrate the scale to maintain accuracy.
It is important to note that a measurement of body weight
by itself has little meaning. For instance, knowing that a
Maine coon weighs 18 lb means little because the cat could
be overweight, underweight, or in ideal body condition. In
addition, body weight can be falsely altered by dehydration
or fluid accumulation. Therefore, body weight should not be
used in isolation.
BODY CONDITION SCORING
Body condition scoring provides a quick and subjective assessment of an animal’s overall body condition. The two
most commonly used scoring systems in small animal practice are a 5-point system, where a body condition score (BCS)
of 3 is considered ideal, or a 9-point system, where a BCS of
4 to 5 is considered ideal. BCS in conjunction with body
weight gives clinicians a more complete perspective on a patient’s body condition and should be recorded in the medical
record at every visit. Limitations of body condition scoring
include the subjectivity inherent in the scoring system and
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interobserver variation. Finally, like body weight, BCS gives
an overall assessment of body condition; it cannot differentiate between body compartments and does not provide any
precise quantitative information concerning alteration in
FFM or lean body mass relative to FM.
nary and respiratory losses of isotope. TBW can be measured
with a precision and accuracy of 1% to 2%. The potential
concern with this technique is the assumption of the hydration factor, which may change with age, sex, species, breed, or
disease.8
MORPHOMETRIC MEASUREMENTS
Extracellular Fluid
Height and circumferential measurements of the abdomen,
hip, thigh, and upper arm are commonly used to estimate
percent body fat in humans. Circumferential measurements
have also been developed to estimate the percent body fat in
cats.6 The Feline Body Mass Index™ is determined by measuring the rib cage circumference at the level of the ninth cranial rib and the leg index measurement (LIM), which is the
distance from the patella to the calcaneal tuber. The percent
body fat can be calculated using a simplified equation, such
as 1.5(rib cage – LIM) – 9, or determined by consulting a reference chart. Cats with more than 30% body fat are candidates for a weight-loss program. The Feline Body Mass Index
is a very simple, yet objective, tool for determining a cat’s
body fat content. In addition, it is particularly valuable for
convincing clients that their cat is indeed overweight and in
need of weight loss.
ECF is an important physiologic component of TBW that may
be altered in illness. ECF can be measured by use of compounds such as inulin, 35S2O3-, 35SO42-, SCN-, Br -, and 82Br - that
distribute within the extracellular space; however, ECF markers may not distribute uniformly in the subcompartments of
the ECF (plasma, interstitium, lymph, connective tissue),
some markers penetrate cells to an extent that cannot be precisely determined, or the markers may bind to some degree
to endogenous components. Bromide is the most useful, safe,
and widely used tracer for determination of extracellular water
(ECW) volume.9 Determination requires high-performance
liquid chromatography, and correction factors can be applied
to account for the Gibbs-Donnan equilibrium, serum water,
and distribution in nonextracellular sites. Simultaneous measurement of ECF and TBW enables the estimation of intracellular water (ICW) volume (i.e., ICW = TBW – ECW). ICW
volume most closely approximates BCM.
DILUTIONAL TECHNIQUES
Total Body Water
BIOELECTRICAL IMPEDANCE ANALYSIS
Dilutional techniques rely on the principle of C1V1 = C2V2;
that is, the volume of a biologic fluid can be calculated following the administration and equilibration of a known concentration of tracer. The total body water (TBW) method
relies on the assumption that fat has negligible water content
and FFM has fairly constant and known water content (73%).
FFM can be calculated as TBW/0.73. Because body weight =
Fat + FFM, an estimation of body composition can be made.
Isotopes of hydrogen (deuterium oxide [D2O] and tritium
oxide [3H2O]), urea, alcohol, N-acetyl-4-aminopyrine, and
H2O18 distribute in the TBW compartment and have been employed to quantify TBW. The approach used in most laboratories is dilution of the stable isotopes D2O or H2O18. These
techniques have been successfully completed in cats7 and are
appropriate for noninvasive studies; however, they do require
expensive analytical equipment. Deuterium and tritium undergo some exchange with nonaqueous H+, and hence can
overestimate TBW by 3% to 5%. Similarly, 18O will exchange
with labile oxygen atoms, and hence can overestimate TBW
by 0% to 1%. Consideration also needs to be given to uri-
BIA is an electrical method of assessing body composition that
has the potential of quantifying TBW, ECW, ICW, BCM, FFM,
and FM. Electrical conductance is used to calculate the composition of the body by measuring the nature of the conductance of an applied electrical current in the patient. Body
fluids and electrolytes are responsible for conductance,
whereas cell membranes produce capacitance. Because adipose tissue is less hydrated than lean body tissues, more adipose tissue results in a smaller conducting volume or path for
current and larger impedance to current passage. FFM contains virtually all the water in the body. Thus, if bioelectrical
impedance is measured, a value for FFM can be determined.
Two types of BIA systems are currently available: single frequency, which applies a 50 kHz current, and multifrequency,
which uses frequencies from 5 kHz to 1,000 KHz. A BIA test
is performed by placing four small electrodes on the body.
The electrical current is introduced into the patient from the
distal electrodes; it then travels through the body and is detected by the proximal electrodes. Low frequencies (e.g., 5
kHz) pass primarily through the ECW because of high cell
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IS MY CAT FAT?
membrane capacitance. In contrast, at higher frequencies the
effect of cell membrane capacitance is diminished so the current flows through both the ICF and ECF environments (or
TBW). The proportion of the current in the ICF and ECF is
frequency dependent.
Reliable BIA requires standardization and control of these
variables, such as hydration status; consumption of food and
water; skin and air temperature; recent physical activity; conductance of the examination table; patient age, size, shape, and
posture; and electrode positioning. However, BIA has been
shown to be a safe, noninvasive, rapid, portable, and reproducible method for estimating body composition in healthy
cats.10,11 Calculation of ECF–ICF takes approximately 1 minute;
hence, BIA provides virtually instantaneous online information of body composition that has never before been available.
DUAL-ENERGY X-RAY ABSORPTIOMETRY
DEXA is a technique originally developed for precise measurement of bone mineral content; however, it is now also used to
measure both body fat and nonbone lean tissue. DEXA uses
photons of two different energy levels (70 and 140 kVp) to distinguish the type and amount of tissue scanned. The x-ray
source is positioned underneath the table supporting the patient, with the detector housed in an arm above the patient.
During a scan, the source and detector move together over the
patient. The detector measures the amount of x-rays that pass
through the subject. The x-rays of the two different energy levels are impeded differently by bone mineral, lipid, and lean tissue. Algorithms are used to calculate both the quantity and type
of tissue in each pixel scanned. DEXA calculates bone mineral
density, bone mineral content, FM, and lean body mass.
DEXA’s low coefficient of variation for measuring bone
mineral content (~1%) makes it a very precise technique.
DEXA is also safe and quick, requiring 10 to 30 minutes for a
whole-body scan. Similar to other body composition tech-
niques, DEXA relies on the assumption that lean body mass
is uniformly hydrated at 0.73 mL water/g.
SUMMARY
With the advent of technology and application of clinically
relevant techniques, veterinarians can offer an objective answer to the question, “Is my cat fat?” The ability to accurately
measure body fat and FFM (lean body mass) is vital for understanding the causes and effects of obesity. In addition,
these techniques allow critical appraisal of the effect of nutrient composition on body composition.
REFERENCES
1. Scarlett JM, Donaghue S. Overweight cats: prevalence and risk factors.
Int J Obes 1994;18:S22-S28.
2. Scarlett JM, Donaghue S. Associations between body condition and disease in cats. JAVMA 1998;212:1725-1731.
3. Keys A, Brozek J. Body fat in adult man. Physiol Rev 1953;33:245-325.
4. Brozek J, Grande F, Anderson JT, et al. Densitometric analysis of body
composition: revision of some quantitative assumptions. Ann N Y Acad
Sci 1963:113-140.
5. Pace N, Rathbun EN. Studies on body composition III: the body water
and chemically combined nitrogen content in relation to fat content. J
Biol Chem 1945;158:685-691.
6. Hawthorne AJ, Butterwick RF. Predicting the body composition of cats:
development of a zoometric measurement for estimation of percentage
body fat in cats. J Vet Intern Med 2000;14:365.
7. Backus RC, Havel PJ, Gingerich RL, et al. Relationship between serum
leptin immunoreactivity and body fat mass as estimated by use of a
novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats. Am J Vet Res 2000;61:796-801.
8. Wang Z, Deurenberg P, Wang W, et al. Hydration of fat-free body mass:
review and critique of a classic body-composition constant. Am J Clin
Nutr 1999;69:833-841.
9. Vaisman N, Pencharz PB, Koren G, et al. Comparison of oral and intravenous administration of sodium bromide for extracellular water measurements. Am J Clin Nutr 1987;46:1-4.
10. Elliott DA. Evaluation of multifrequency bioelectrical impedance analysis for the assessment of extracellular and total body water in healthy
cats. J Nutr 2002;132(6 suppl 2):1757S-1759S.
11. Stanton CA, Hamar DW, Johnson DE, et al. Bioelectrical impedance
and zoometry for body composition analysis in domestic cats. Am J Vet
Res 1992;53:251-257.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Adipokines and Their Importance in Obese Cats
M. Anne Hickman, DVM, PhD, DACVN
Global Research and Development, Cardiovascular, Metabolic, and Endocrine Diseases,
Pfizer, Inc., New London, Connecticut
Obesity is a chronic disease that is growing at an alarming rate
in both humans and their feline companions. Obesity increases
the risk for a number of metabolic abnormalities in humans and
cats, including insulin resistance, type 2 diabetes mellitus
(T2DM), hypertension, and dyslipidemia.1–7 Obesity has been
regarded as a simple energy imbalance, with energy intake exceeding energy expenditure; however, this view has changed over
the last 10 years based on a greater understanding of adipose tissue and its function in normal states and disease. We now know
that adipose tissue reserves are carefully maintained and regulated by complex systems that integrate food intake, substrate
partitioning, and energy expenditure and can be influenced by
environmental conditions and individual genetics.8,9 Obesity results from dysregulation of these complex systems and is a disease that is now recognized to have significant metabolic and
health implications. Alterations in the secretion of adipokines,
protein signals, and factors originating in adipose tissue underlie many of the abnormalities in obesity.
White adipose tissue has been viewed as a passive storage
depot for excess energy in the form of triglycerides and a site
of release of fatty acids when energy is needed. This view was
partially held because adipose tissue appears to be a simple
tissue composed primarily of large cells filled with triglyceride
(~85% of content)9; however, white adipose tissue is now understood to be a complex tissue composed of multiple functional cell types, including mature adipocytes, preadipocytes,
fibroblasts, endothelial cells, and macrophages, and the cell
composition can change in response to various conditions.10,11
Functionally, white adipose tissue is an active endocrine and
paracrine organ that secretes a wide array of mediators that
participate in regulation of diverse metabolic processes, including food intake, energy expenditure, lipid and carbohydrate metabolism, angiogenesis, reproduction, vascular
remodeling, blood pressure, and coagulation. A major advance in our understanding of adipose tissue was made with
the discovery of leptin, a secreted signal from adipose tissue to
the hypothalamus that signals the size of body fat stores as
part of its wide range of biologic functions.12–14 In addition to
30
Proceedings, 2007 Nestlé Purina Nutrition Forum
leptin, many other adipokines have been discovered and are
now in the process of being characterized.
Adipokines have important physiologic effects on multiple
organs, including the brain, liver, muscle, adipose (paracrine
effect) bone, reproductive organs, immune cells, and blood
vessels; however, most adipokines are dysregulated in
response to alterations of body fat mass, one of the best examples being obesity.15–17 Adipokine responses are also influenced by the distribution of body fat increase, as excessive fat
is not only stored in adipose tissue, but is abnormally deposited in muscle and liver tissue as well.17,18 The majority of
adipokines studied to date are hypersecreted in obesity, a notable exception being adiponectin, which declines. Adipokine
alterations cause abnormalities in insulin action, glucose and
fat metabolism, immune function, coagulation, and endothelial cell function, eventually leading to a proinflammatory state characterized by insulin resistance and altered
immune function.15–19 Adipokine alterations appear to provide the link between obesity-related diseases as diverse as
T2DM and cancer. The list of adipokines is ever increasing and
includes leptin, adiponectin, resistin, retinol-binding protein
4 (RBP4), apelin, omentin, monocyte chemoattractant protein-1 (MCP-1), transforming growth factor-β, interleukin
(IL)-1β, IL-6, IL-8, IL-10, macrophage migration inhibitory
factor, haptoglobin, serum amyloid-A, nerve growth factor,
adipsin, plasminogen activator inhibitor-1 (PAI-1), fastinginduced adipose factor, metallothionein, angiotensinogen,
complement C3, fibronectin, and vascular endothelial growth
factor. This review will attempt to highlight a few of the better-understood adipokines and their role in obesity.
LEPTIN
Leptin, a 16-kDa, cytokine-like protein, is encoded by the ob
gene and is secreted primarily by adipose tissue in proportion to body fat stores and immediate nutritional state.12,20–22
Leptin is a pleiotropic hormone with multiple actions on the
brain, pancreas, liver, immune system, and adipose.23 The importance of leptin was first investigated in loss-of-function
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ADIPOKINES AND THEIR IMPORTANCE IN OBESE CATS
rodent models of obesity, such as ob/ob and db/db mice.
Leptin is one of a few adipokines that has also been investigated in cats. Several studies have demonstrated that, similar
to other species, plasma leptin concentrations are correlated
with body fat content and concentration increase or decrease
in response to weight gain or weight loss, respectively.24–29 Although few studies have investigated the physiologic effects of
leptin in cats, it is likely that leptin behaves similarly in cats
as it does in other species.
Leptin is normally a signal of energy sufficiency that results
in decreased food intake and increased energy expenditure, actions that are mediated primarily by central sympathetic activation.30–33 Centrally, leptin interacts with hypothalamic pathways
involved in energy regulation and acts to inhibit release of the
orexigenic peptides, neuropeptide Y and agouti gene-related
peptide, and increase release of the anorexigenic peptides, proopiomelanocortin and cocaine- and amphetamine-regulated
transcript. In peripheral tissue, leptin action is mediated in part
by increased expression and activation of AMP-activated protein
kinase (AMPK).34,35 AMPK inhibits the enzyme acetyl–coenzyme
A (CoA) carboxylase, leading to reduced levels of malonyl-CoA
and increased entry of fatty acids into the mitochondria, where
they undergo β-oxidation. Leptin may also stimulate fatty acid
oxidation by activation of peroxisome proliferator-activated receptor-α (PPARα).36 In liver, pancreatic islet, and adipose tissue,
leptin inhibits the expression of sterol response element-binding protein-1c, resulting in inhibition of lipogenesis in these tissues.37 Through these mechanisms and others, leptin causes
decreased triglyceride content in tissue, such as skeletal muscle,
liver, and pancreas, and decreased circulating concentrations of
fatty acids; these effects, among others, lead to improved insulin
sensitivity. Leptin-deficient and leptin-resistant rodents have severe insulin resistance, which can be ameliorated by leptin administration, even before reductions in body weight38–40;
however, obese humans and cats have high circulating levels of
leptin but do not benefit from its positive metabolic effects, leading to the concept of leptin resistance. Although this concept is
now widely accepted, the molecular basis is still controversial
and under active investigation.
ADIPONECTIN
Adiponectin, or adipocyte complement-related protein, is a
35-kDa protein that is almost exclusively expressed in white
adipose tissue.41,42 In humans, adiponectin levels are inversely
correlated with body fat content, hepatic fat content, dyslipidemia, and insulin resistance.43–45 Levels are very low in pa-
tients with T2DM and coronary artery disease, and low
adiponectin concentrations have been proposed as risk markers for these diseases. Adiponectin concentrations are decreased in obesity but can be increased by weight loss or
treatment with thiazoladinediones.46 Few data are available in
cats regarding adiponectin, but plasma concentrations have
been shown to correlate with body fat mass and to increase
in response to weight loss.29
In mice and humans, adiponectin has been shown to function as both an insulin-sensitizing factor and an antiinflammatory agent, antagonizing many of the negative effects of
tumor necrosis factor (TNF)-α.46 Overexpression or exogenous
administration of adiponectin results in glucose lowering and
amelioration of insulin resistance in murine models of obesity
and diabetes. Adiponectin is the most abundantly secreted
adipokine and circulates at high concentrations (1000-fold
higher than most polypeptide hormones).43 It is rarely found
as a monomer and circulates in plasma as trimer, hexamer
(low molecular weight form), or multimeric forms of 12 to
18 subunits (high molecular weight form).47 The various
forms appear to have different roles, with the high molecular
weight form having a predominant action in the liver. Similar
to leptin, adiponectin activates AMPK and increases fatty acid
oxidation in skeletal muscle, liver, and other tissues.19,48 It also
causes enhanced glucose uptake in skeletal muscle due to increased translocation of glucose transporter 4 (GLUT 4).49
These effects, which lead to decreased triglyceride content in
tissue and enhanced insulin sensitivity, and its emerging antiinflammatory role make adiponectin one of the key candidate molecules mediating negative changes in obesity.
RESISTIN
Resistin is a 12-kDa peptide hormone expressed primarily by
adipocytes in rodents and macrophages in humans.50 Circulating concentrations of resistin are increased in rodent models of diet-induced and genetic obesity.51 Based on its actions
in rodents to increase blood glucose and insulin levels and to
impair insulin function, resistin was believed to be a major
link between obesity and insulin resistance. In addition, deletion of the resistin gene in ob/ob mice leads to improved glucose tolerance and insulin sensitivity through increased
AMPK activity in liver and increased insulin-mediated glucose disposal in muscle and adipose tissue52; however,
human resistin shares only 59% identity with murine resistin
and is expressed primarily in macrophages, not in
adipocytes.53 In humans, there is no convincing link between
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plasma resistin concentrations and body fat stores or insulin
resistance. Tissue sites and the role of resistin in obese and
diabetic cats are unknown, but if these factors in cats are similar to those in rodents, they could contribute to obesity-related insulin resistance.
RETINOL-BINDING PROTEIN
has been done in cats to investigate inflammatory adipokine
responses to obesity, although data gleaned from a study on
dogs demonstrate that canine adipose tissue expresses many
of these cytokines.62
REGIONAL ADIPOSE EFFECTS
RBP4, a 21-kDa protein, is another adipokine implicated in
obesity-related insulin resistance, although current data are
still controversial.54 Mice lacking GLUT 4, specifically in adipose tissue, are insulin resistant in muscle and liver and have
increased circulating concentrations of RBP4.55 These findings led to the hypothesis that RBP4 is secreted by adipose
tissue in response to plasma glucose concentrations. In humans, circulating concentrations of RBP4 are correlated with
adiposity, abdominal obesity, insulin levels, and insulin resistance.56 Levels are increased in humans with impaired glucose tolerance or diabetes and are decreased after weight loss.
Adipokine expression and secretion appear to be influenced
in humans and rodents by regional adipose tissue distribution.18,19 These findings likely have importance in cats as well,
but data are not yet available. Visceral (omental and mesenteric), intramyocellular, and intrahepatic fat content are reported to have greater effects on insulin resistance and
inflammation than subcutaneous fat, and many of these effects appear to be related to differential adipokine secretion.
Differences are also reported in men compared to women
and in different ethnic groups. Data in cats on the effects of
regional adipose tissue distribution could be important in
our understanding of risk assessment for obese cats.
INFLAMMATORY ADIPOKINES
CONCLUSION
Inflammatory and prothrombotic adipokines also have increased expression and release in obesity.8–11,15,16,57 The best
studied of these adipokines are IL-6, TNF-α, and PAI-1. In
obesity, the number of macrophages present in white adipose tissue is increased, and adipocytes and adipose-tissueassociated macrophages secrete elevated concentrations of
inflammatory cytokines.11,16 Inflammatory adipokines not
only play a role in the proinflammatory state of obesity but
also may mediate some of obesity’s effects on insulin sensitivity.58 TNF-α and IL-6 impair insulin signaling and have actions that lead to insulin resistance; the significance of these
effects in humans is still controversial. TNF-α activates the
transcription factor nuclear factor-κB, which results in proinflammatory gene expression changes in many tissues.59 In
adipocytes, these changes include decreased gene expression
of adiponectin and increased expression of PAI-1 and complement C3. Some of the mediators increased by TNF-α are
also proposed to be links between obesity and hypertension.60 Increased inflammatory adipokine release from adipose tissue has been proposed to be due to hypoxia (caused
by poor circulation due to expanded adipose tissue mass)16
and altered communication between adipocytes and
macrophages within adipose tissue. Adipose tissue levels of
MCP-1, produced by monocytes and adipocytes, are elevated
with increasing adiposity.61 This leads to increased recruitment of macrophages as adipose tissue expands. Little work
In summary, our knowledge of adipose tissue as an important endocrine organ is rapidly increasing. Adipokines play
an important and diverse role in multiple facets of normal
metabolism and physiology. Adipokines can become dysregulated in obesity and may have direct causal links to many
of the associated abnormalities, although more research in
this area is required for a full understanding. In all species, including cats, some adipokines appear to be common and
function similarly, but other factors have more species specificity. Further research in cats is warranted to understand the
role of these fascinating molecules so that therapies for diseases such as obesity and T2DM can be developed.
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4. German AJ. The growing problem of obesity in dogs and cats. J Nutr
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5. Lund EM, Armstrong PJ, Kirk CA, Klausner JS. Prevalence and risk factors for obesity in adult cats from private US veterinary practices. Int J
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6. Panciera DL, Thomas CB, Eicker SW, Atkins CE. Epizootiologic patterns of diabetes mellitus in cats: 333 cases (1980–1986). JAVMA 1990;197:154-158.
7. Scarlett JM, Donoghue S. Associations between body condition and disease in cats. JAVMA 1998;212:1725-1731.
8. Badman MK, Flier JS. The adipocyte as an active participant in energy
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9. Trayhurn P, Bing C, Wood IS. Adipose tissue and adipokines: energy
regulation from the human perspective. J Nutr 2006;136:1935S-1939S.
10. Hausman GJ. The comparative anatomy of adipose tissue. In: Cryer A,
Van RLR, eds. New Perspectives in Adipose Tissue: Structure, Function and
Development. London: Butterworths; 1985:1-21.
11. Weisberg SP, McCann D, Desai M, et al. Obesity is associated with
macrophage accumulation in adipose tissue. J Clin Invest 2003;112:
1796-1808.
12. Zhang Y, Proenca R, Maffei M, et al. Positional cloning of the mouse
obese gene and its human homologue. Nature 1994;372:425-432.
13. Chen H, Charlat O, Tartaglia LA, et al. Evidence that the diabetes gene
encodes the leptin receptor: identification of a mutation in the leptin receptor gene in db/db mice. Cell 1996;84:491-495.
14. Tartaglia LA, Dembski M, Weng X, et al. Identification and expression
cloning of a leptin receptor, OB-R. Cell 1995;83:1263-1271.
15. Murdolo G, Smith U. The dysregulated adipose tissue: a connecting link
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16. Trayhurn P, Wood IS. Adipokines: inflammation and the pleiotropic
role of white adipose tissue. Br J Nutr 2004;92:347-355.
17. Yildiz BO, Suchard MA, Wong ML, et al. Alterations in the dynamics of
circulating ghrelin, adiponectin, and leptin in human obesity. Proc Natl
Acad Sci USA 2004;101:10434-10439.
18. Rattarasarn C. Physiological and pathophysiological regulation of regional adipose tissue in the development of insulin resistance and type
2 diabetes. Acta Physiol 2006;186:87-101.
19. Dyck DJ, Heigenhauser GJF, Bruce CR. The role of adipokines as regulators of skeletal muscle fatty acid metabolism and insulin sensitivity.
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20. Ahima RS, Prabakaran D, Mantzoros C, et al. Role of leptin in the neuroendocrine response to fasting. Nature 1996;382:250-252.
21. Sivitz W, Wayson S, Bayless M, et al. Leptin and body fat in type 2 diabetes
and monodrug therapy. J Clin Endocrinol Metab 2003;88:1543-1553.
22. Considine RV, Sihna MK, Heiman ML, et al. Serum immunoreactiveleptin concentrations in normal-weight and obese humans. N Engl J
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23. Bjorbaek C, Kahn BB. Leptin signaling in the central nervous system
and the periphery. Recent Prog Horm Res 2004;59:305-331.
24. Backus RC, Havel PJ, Gingerich RL, Rogers QR. Relationship between
serum leptin immunoreactivity and body fat mass as estimated by use
of a novel gas-phase Fourier transform infrared spectroscopy deuterium
dilution method in cats. Am J Vet Res 2000;61:796-801.
25. Appleton DJ, Rand JS, Sunvold GD. Plasma leptin concentrations in
cats: reference range, effect of weight gain and relationship with adiposity as measured by dual energy X-ray absorptiometry. J Feline Med
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26. Appleton DJ, Rand JS, Sunvold GD. Plasma leptin concentrations are independently associated with insulin sensitivity in lean and overweight
cats. J Feline Med Surg 2002;4:83-93.
27. Kanchuk ML, Backus RC, Calvert CC, et al. Neutering induces changes
in food intake, body weight, plasma insulin and leptin concentrations
in normal and lipoprotein lipase-deficient cats. J Nutr 2002;132:1730S1732S.
28. Shibata H, Sasaki N, Honjoh T, et al. Feline leptin: immunogenic and
biological activities of the recombinant protein, and its measurement by
ELISA. J Vet Med Sci 2003;65:1207-1211.
29. Hoenig M, Thomaseth K, Waldron M, Ferguson DC. Insulin sensitivity,
fat distribution, and adipocytokine response to different diets in lean
and obese cats before and after weight loss. Am J Physiol Regul Integr
Comp Physiol 2006;292:R227-R234.
30. Cowley MA, Smart JL, Rubinstein M, et al. Leptin activates anorexigenic
POMC neurons through a neural network in the arcuate nucleus. Nature
2001;411:480-484.
31. van den Top M, Lee K, Whyment AD, et al. Orexigen-sensitive
NPY/AgRP pacemaker neurons in the hypothalamic arcuate nucleus.
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32. Balthasar N, Coppari R, McMinn J, et al. Leptin receptor signaling in
POMC neurons is required for normal body weight homeostasis. Neuron 2004;42:983-991.
33. Coppari R, Ichinose M, Lee CE, et al. The hypothalamic arcuate nucleus:
a key site for mediating leptin’s effects on glucose homeostasis and locomotor activity. Cell Metab 2005;1:63-72.
34. Steinberg GR, Rush JW, Dyck DJ. AMPK expression and phosphorylation are increased in rodent muscle after chronic leptin treatment. Am
J Physiol Endocrinol Metab 2003;284:E648-E654.
35. Minokoshi Y, Kim YB, Peroni OD, et al. Leptin stimulates fatty-acid oxidation by activating AMP-activated protein kinase. Nature 2002;415:339-343.
36. Lee Y, Yu K, Gonzales F, et al. PPAR alpha is necessary for the lipogenic
action of hyperleptinemia on white adipose and liver tissue. Proc Natl
Acad Sci USA 2002;99:11848-11853.
37. Nogalska A, Sucajtys-Szulc E, Swierczynski J. Leptin decreases lipogenic
enzyme gene expression through modification of SREBP-1c gene expression in white adipose tissue of aging rats. Metabolism 2005;54:1041-1047.
38. Halaas JL, Gajiwala KS, Maffei M, et al. Weight-reducing effects of the
plasma protein encoded by the obese gene. Science 1995;269:543-546.
39. Campfield LA, Smith FJ, Guisez Y, et al. Recombinant mouse OB protein: evidence for a peripheral signal linking adiposity and central neural networks. Science 1995;269:546-549.
40. Pelleymounter MA, Cullen MJ, Baker MB, et al. Effects of the obese gene
product on body weight regulation in ob/ob mice. Science 1995;
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41. Scherer PE, Williams S, Fogliano M, et al. A novel serum protein similar to C1q, produced exclusively in adipocytes. J Biol Chem 1995;270:
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42. Hu E, Liang P, Spiegelman BM. AdipoQ is a novel adipose-specific gene
dysregulated in obesity. J Biol Chem 1996;271:10697-10703.
43. Kadowaki T, Yamauchi T, Kubota N, et al. Adiponectin and adiponectin
receptors in insulin resistance, diabetes, and the metabolic syndrome. J
Clin Invest 2006;116:1784-1792.
44. Arita Y, Kihara S, Ouchi N, et al. Paradoxical decrease of an adiposespecific protein, adiponectin, in obesity. Biochem Biophys Res Commun
1999;257:79-83.
45. Weyer C, Funahashi T, Tanaka S, et al. Hypoadiponectinemia in obesity
and type 2 diabetes: close association with insulin resistance and hyperinsulinemia. J Clin Endocrinol Metab 2001;86:1930-1935.
46. Whitehead JP, Richards AA, Hickman IJ, et al. Adiponectin: a key
adipokine in the metabolic syndrome. Diabetes Obes Metab 2006;8(3):
264-280.
47. Pajvani UB, Hawkins M, Combs TP, et al. Complex distribution, not absolute amount of adiponectin, correlates with thiazolidinedione-mediated improvement in insulin sensitivity. J Biol Chem 2004;279:
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48. Yamauchi T, Kamon J, Minokoshi Y, et al. Adiponectin stimulates glucose utilization and fatty-acid oxidation by activating AMP-activated
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49. Ceddia RB, Somwar R, Maida A, et al. Globular adiponectin increases
GLUT 4 translocation and glucose uptake but reduces glycogen synthesis in rat skeletal muscle cells. Diabetologia 2005;48:132-139.
50. Steppan CM, Lazar MA. The current biology of resistin. J Intern Med
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51. Steppan CM, Bailey ST, Bhat S, et al. The hormone resistin links obesity
to diabetes. Nature 2001;409:307-312.
52. Qi Y, Nie Z, Lee YS, et al. Loss of resistin improves glucose homeostasis
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53. Banerjee RR, Lazar MA. Resistin: molecular history and prognosis. J Mol
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54. Yang Q, Graham TE, Mody N, et al. Serum retinol binding protein 4
contributes to insulin resistance in obesity and type 2 diabetes. Nature
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55. Abel ED, Peroni O, Kim JK, et al. Adipose-selective targeting of the
GLUT4 gene impairs insulin action in muscle and liver. Nature
2001;409:729-733.
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56. Graham TE, Yang Q, Bluher M, et al. Retinol-binding protein 4 and insulin resistance in lean, obese, and diabetic subjects. N Engl J Med
2006;354:2552-2563.
57. Kern PA, Saghizadeh M, Ong JM, et al. The expression of tumor necrosis factor in human adipose tissue: regulation by obesity, weight loss,
and relationship to lipoprotein lipase. J Clin Invest 1995;95:2111-2119.
58. Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of
tumor necrosis factor-alpha: direct role in obesity-linked insulin resistance. Science 1993;259:87-91.
59. Lyon CJ, Law RE, Hsueh VA. Minireview: adiposity, inflammation, and
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atherogenesis. Endocrinology 2003;144:2195.
60. Brasier AR, Li J, Wimbish KA. Tumor necrosis factor activates angiotensinogen gene expression by the Rel A transactivator. Hypertension
1996;27:1009.
61. Kanda H, Tateya S, Ttamori Y, et al. MCP-1 contributes to macrophage
infiltration into adipose tissue, insulin resistance, and hepatic steatosis
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62. Eisele I, Wood IS, German AJ, et al. Adipokine gene expression in dog
adipose tissue and dog white adipocytes differentiated in primary culture. Horm Metab Res 2005;37:474-481.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
New Technologies for Pharmaceutical
and Nutrition Research
Marnie L. MacDonald, PhD
MM Health Advocates, Scottsdale, Arizona
The Nestlé Purina Nutrition Forum, honoring Drs. James
Morris and Quinton Rogers, provides an opportunity to reflect not only on the legacy of their work and its contributions to animal health but also on the evolution of animal
nutrition and medicine over the course of their careers. This
presentation describes the evolution of approaches to the
study of nutrient function over the past several decades, including whole animal nutrition, metabolism, and physiology; the molecular mechanisms of nutrient metabolism and
regulation; and the study of these mechanisms in the context
of living cells. The parallels between the fields of nutrition,
pharmacology, and toxicology in the wake of new technologies for illuminating the mechanisms of action of nutrients
and drugs at the cellular level is also described.
WHOLE ANIMAL NUTRITION, METABOLISM,
AND PHYSIOLOGY
The legacy of Rogers’ and Morris’ collaboration results from
their classic studies in whole animal nutrition, combined
with a deep understanding of nutritional biochemistry and
metabolism, to define the unique dietary requirements of
cats.1–3 It is now widely appreciated that these requirements
are consistent with the evolutionary influence of a strict carnivorous diet. The studies by Rogers and Morris of cats’ essential amino acid requirements not only defined the dietary
requirements but also suggested that the extreme response of
cats to arginine deficiency resulted from certain biochemical
defects in the synthesis or transport (or both) of urea cycle
intermediates. They showed that ornithine prevents the hyperammonemia of arginine deficiency but does not provide
for normal growth and that citrulline is capable of substituting for arginine in the diet.4,5 With regard to essential fatty
acids, cats fed diets lacking arachidonate have extremely low
levels of arachidonic acid in plasma and erythrocyte lipids6 as
a result of a low level of the first enzyme in the desaturation
pathway.7 Linoleate prevents or ameliorates many, but not
all, of the signs of essential fatty acid deficiency in cats.8–11 In
particular, linoleate appears to supply the needs of male cats
for reproduction and prevention of testis degeneration, but
female cats require preformed arachidonate for successful
pregnancies and normal litters.8,9
The role of arachidonic acid as an essential component of
membrane phospholipids and as a precursor for the
eicosanoids allowed us to formulate some hypotheses regarding the consequences of arachidonate deficiency in cats.
Because thromboxane A2, a potent thrombotic agent, is derived from arachidonic acid, we hypothesized that a deficiency
of dietary arachidonate would affect platelet function. Consistent with this hypothesis, we showed that arachidonate is a
requirement in cats for normal platelet aggregation.11 The central role of arachidonate in cellular function in mammals has
subsequently been highlighted by the discoveries of various
enzymes with a preference for arachidonoyl-containing substrates. Selective enzymes include the arachidonate-selective
acyl-CoA synthetase,12 acyl-CoA thioesterase,13 and phospholipase A214 as well as a membrane-bound arachidonoyl-specific diacylglycerol kinase.15 The latter enzyme functions to
enrich cell membranes with arachidonic acid–containing
phospholipids by selectively phosphorylating arachidonoyldiacylglycerol. The arachidonic acid–selective acyl-CoA synthetase is a hormone-dependent, obligatory protein in the
signal transduction pathway of steroidogenic hormones.16
Many of these effects occur at the level of the whole cell
and result in changes in cell motility, growth, adhesion, and
other properties. Cells are complex systems in which a multitude of biochemical reactions and molecular events take place
concurrently and need to be finely orchestrated to preserve
cell homeostasis and direct cell-specific functions. For example, some of the effects of arachidonate deficiency may be related to the essential role of arachidonate in preserving cell
membrane fluidity and architecture, including the interactions
of proteins within lipid rafts. It has been shown that arachidonate is important for the maintenance of numerous cellular functions, including the functions of receptors in the
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membrane and nucleus of the cell.17 Finally, arachidonate and
other polyunsaturated fatty acids directly modulate gene transcription by binding to nuclear transcription factors, including
peroxisome proliferator-activated receptors (PPARs).18 Because cells are controlled by the physical interactions of these
proteins, cell-based methods may provide an efficient way to
understand how nutrients and other small molecules affect
not just their primary targets but also individual or multiple
biochemical pathways within cells.
MOLECULAR MECHANISMS OF NUTRIENT
METABOLISM AND REGULATION
The field of molecular cell biology has evolved substantially
over the past 10 years, enabling such studies on a large scale.
Cellular screening techniques allow for the study of the effects of exogenous molecules (e.g., nutrients, drugs, toxicants)
in living cells. The ability to work with live cells at the level of
individual proteins, including receptors, signaling proteins,
and enzymes, opens the door to understanding the links between the biochemical function or metabolism of a nutrient
and its role in health and disease. Specifically, the development of new technologies based on real-time imaging of fluorescent indicators has enabled the direct visualization and
quantification of these events in real time.
Whole-cell assay technologies vary with respect to the
assay principle but largely have in common a form of luminescence or fluorescence for detection. Luminescent, fluorescent, or bioluminescent signals are easily detected and
quantified with a variety of automated or high-throughput
instrumentation systems, including fluorescence multi-well
plate readers, fluorescence activated cell sorters, and automated cell-based imaging systems that provide spatial resolution of the signal at the subcellular level. A variety of
instrumentation systems have been developed to automate
these measurements, allowing the accumulation of data on
thousands of living cells arrayed in microtiter plates. If combined with a suitable assay system, the effects of any compound can be measured on a large scale at the level of any
cellular process or pathway, whether in the membrane, cytosol, or nucleus of the cell, of any cell type. All that is needed
is a universal quantitative method of monitoring the dynamic
processes that occur at the level of the proteins, which are the
targets of the compound (e.g., nutrient, drug) of interest.
Dr. Stephen Michnick and colleagues19–21 at the University
of Montreal proposed that cell-based measurements of protein–protein interactions could be used to monitor the dy36
Proceedings, 2007 Nestlé Purina Nutrition Forum
namic association and dissociation of proteins, both to monitor the activity of a biochemical pathway in living cells and
to directly study the effects of chemicals on the pathways.
Michnick’s laboratory developed protein fragment complementation assays (PCAs), a general strategy for monitoring
the dynamics of protein–protein interactions in vivo and in
real time. PCAs enable fluorescent, real-time analysis of signaling events by measuring the association, dissociation, and
movements of protein–protein complexes within cells. PCAs
are created by expressing mammalian genes linked in frame
to fragments of rationally dissected reporter genes. The association of two proteins of interest brings together complementary reporter fragments and enables productive folding
of the fragments into an active structure that generates a fluorescent or luminescent signal. The resulting signals can be
spatially localized and quantified in living cells using highcontent imaging instrumentation.22,23 We and others have recently applied these methods to de novo drug discovery in
the identification of the mechanism of action of nutrients
and hormones and in the discovery of new uses for known
drugs.24,25 These new technologies will aid in the design of in
vivo studies to advance our understanding of the relationships between the biochemical functions of nutrients and
drugs and their functions in health and disease.
REFERENCES
1. Morris JG, Rogers QR. Metabolic basis for some of the nutritional peculiarities of the cat. J Small Anim Pract 1982;23:599-613.
2. MacDonald ML, Rogers QR, Morris JG. Nutrition of the domestic cat, a
mammalian carnivore. Annu Rev Nutr 1984;4:521-562.
3. Morris JG. Idiosyncratic nutrient requirements of cats appear to be dietinduced evolutionary adaptations. Nutr Res Rev 2002;15:153-168.
4. Morris JG, Rogers QR, Winterrowd DL, Kamikawa EM. The utilization
of ornithine and citrulline by the growing kitten. J Nutr 1979;109:724729.
5. Rogers QR, Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109:718-723.
6. MacDonald ML, Rogers QR, Morris JG. Role of linoleate as an essential
fatty acid for the cat independent of arachidonate synthesis. J Nutr
1983;113:1422-1433.
7. Pawlosky RJ, Barnes A, Salem N. Essential fatty acid metabolism in the
feline: relationship between liver and brain production of long-chain
polyunsaturated fatty acids. J Lipids Res 1994;35:2032-2040.
8. MacDonald ML, Anderson BC, Rogers QR, et al. Essential fatty acid requirements of cats: pathology of essential fatty acid deficiency. Am J Vet
Res 1984;45:1310-1317.
9. MacDonald ML, Rogers QR, Morris JG, Cupps PT. Effects of linoleate
and arachidonate deficiencies on reproduction and spermatogenesis in
the cat. J Nutr 1984;114:719-726.
10. Morris JG. Do cats need arachidonic acid in the diet for reproduction?
J Anim Physiol Anim Nutr 2004;8:131-137.
11. MacDonald ML, Rogers QR, Morris JG. Effects of dietary arachidonate
deficiency on the aggregation of cat platelets. Comp Biochem Physiol
1984;78(suppl C):123-126.
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NEW TECHNOLOGIES FOR PHARMACEUTICAL AND NUTRITION RESEARCH
12. Kang MJ, Fujino T, Sasano H, et al. A novel arachidonate-preferring acylCoA synthetase is present in steroidogenic cells of the rat adrenal, ovary,
and testis. Proc Natl Acad Sci USA 1997;94:2880-2884.
18. Benatti P, Peluso G, Nicolai R, Calvani M. Polyunsaturated fatty acids:
biochemical, nutritional and epigenetic properties. J Am Coll Nutr
2004;23:281-302.
13. Maloberti P, Lozano RC, Mele PG, et al. Concerted regulation of free
arachidonic acid and hormone-induced steroid synthesis by acyl-CoA
thioesterases and acyl-CoA synthetases in adrenal cells. Eur J Biochem
2002;259:5599-5607.
19. Michnick SW. Proteomics in living cells. Drug Discov Today 2004;9:262-267.
14. Suga K, Kawasaki T, Blank ML, Snyder F. An arachidonoyl (polyenoic)specific phospholipase AS activity regulates the synthesis of platelet-activating factor in granulocytic hl-60 cells. J Biol Chem 1990;265(21):
12363-12371.
21. Campbell-Valois FX, Michnick SW. Chemical biology on PINs and
NeeDLes. Curr Opin Chem Biol 2005;9:31-37.
15. MacDonald ML, Mack KF, Williams BW, et al. A membrane-bound diacylglycerol kinase that selectively phosphorylates arachidonoyl-diacylglycerol. J Biol Chem 1988;263:1584-1592.
16. Cornejo Maciel F, Maloberti P, Neuman I, et al. An arachidonic acidpreferring acyl-CoA synthetase is a hormone-dependent and obligatory
protein in the signal transduction pathway of steroidogenic hormones.
J Mol Endocrinol 2005;34:655-666.
17. Martins de Lima T, Gorjão R, Hatanaka E, et al. Mechanisms by which
fatty acids regulate leucocyte function. Clin Sci 2007;113:65-77.
20. Michnick SW. Exploring protein interactions by interaction-induced
folding of proteins from complementary peptide fragments. Curr Opin
Struct Biol 2001;11:472-477.
22. MacDonald ML, Westwick JK. Exploiting network biology to improve
drug discovery. In: Taylor DL, Haskins JR, Giuliano KA, eds. High Content Screening: A Powerful Approach to Systems Cell Biology and Drug Discovery. Totowa, NJ: Humana Press; 2006.
23. Yu H, West M, Keon BH, et al. Measuring drug action in the cellular
context using protein-fragment complementation assays. Assay Drug Dev
Technol 2003;1:811-822.
24. MacDonald ML, Lamerdin J, Owens S, et al. Identifying off-target effects and hidden phenotypes of drugs in human cells. Nat Chem Biol
2006;2:329-337.
25. Owens J. Dirty drugs’ secrets uncovered. Nat Rev Drug Discov 2006;5:1.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Is the Aging Feline Kidney a Mortality Antagonist?
Dennis F. Lawler, DVM
Nestlé Research Center, St. Louis, Missouri
Diseases of advanced life have been viewed as chance events
that potentially end life. This understanding is reflected in
cataloging approaches to describing diseases of aging and
recommending preventive or therapeutic responses.1,2 In a
different view, aging phenotypes often are associated with
complex underlying biology at genomic, cellular, organ, and
systemic levels. Prolonged investment of metabolic energy
at this level of complexity is not consistent with chance
events that simply disrupt “natural aging.” Rather, perhaps
late-life diseases should be regarded as integral to the aging
process, with response programming that is plastic and
adaptable.3,4
Within this redirected frame of reference, numerous aspects of aging have been evaluated from a database consisting of postmortem findings from nearly 700 adult cats that
were maintained for life as residents of the same colony from
1979 to 2001. Cats that died or were euthanized because of
renal disease lived longer than those that died from other
causes. The cats that died from renal disease had higher but
uniform mean renal histologic scores across ages compared
with cats that died from other causes.5
Among cats that died from nonrenal causes but that had
histologic renal changes, mean lifespan was longer than in
cats without renal changes or renal causes of death. Cats that
succumbed to nonrenal causes of death also were evaluated
across categories of death-causing diseases. Specific problems
did not underlie the difference in mean age at death between
these two subgroups, underscoring the observation that the
outcomes were not consequent to the structure and function
of the colony. Additionally, the inbreeding coefficients in this
colony were low.
Cats that succumbed to renal failure frequently had morphologic and preterminal metabolic changes, suggesting varying but substantial retained functional capacity. Although
standard clinical chemistry is insensitive, the total body of
data suggests also that other factors may direct transition to
renal failure. Considering histological morphology, the usual
sequelae of ischemia (cell swelling, karyolysis, lysosomal rupture, massive inflammation) are not commonly observed in
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Proceedings, 2007 Nestlé Purina Nutrition Forum
cat kidneys or in a similar mouse model.6–8 In addition, the
low frequency of acute renal lesions among a large number of
cats that died from nonrenal causes suggests that a discrete
initializing event, such as ischemic episode, infection, or toxicity, may not be a prominent feature of this process.
In a feline model of renal tubular disease, fibrosis was
principally peritubular, suggesting that hypoxic sequelae result mainly from local compromise of diffusion.8 In a murine
renal model, upregulated Fas (apoptosis-mediating surface
antigen; APO1, CD95) in tubular epithelial cells was shown
to bind to Fas ligand of adjacent tubular cells, suggesting that
tubular loss is a signaled (fratricidal) apoptosis.7 Thus, the
histologic nature of tubule loss in feline and murine models
appears to be more compatible with an adaptive mechanism
that operates at the cellular level. Frequent observation of
tubulointerstitial changes in younger adults documents early
onset, which also is compatible with defensive adaptation because symptomatic renal failure is much less frequent during
early adulthood but very common during late adult life.
A specific underlying explanation for these observations
is not obvious at present. Domestic cats are seasonally polyestrous and multiparous, with declining fertility often initially
detectable over the 84- to 96-month age range.9–11 Thus, the
onset of tubulointerstitial changes that appear before this age
may have evolved as one homeostatic response to help preserve a fertile reproductive lifespan by selective elimination of
dysfunctional renal tubular cells and nephrons. Such an
adaptation could, for example, increase the likelihood of successful reproduction through greater metabolic stability. A hypothesis that stress-response programming of this type
evolved to modulate population survival is within the present scope of the debate about aging theories.12,13 However,
this hypothesis is incomplete because it does not account for
a long postreproductive lifespan. Indeed, a long postreproductive lifespan can occur even in simple organisms. Additionally, Mitteldorf 13 suggests that longevity and fecundity
may have evolved independently. This idea jeopardizes the
older hypothesis that longevity and reproduction represent
evolutionary trade-offs.
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IS THE AGING FELINE KIDNEY A MORTALITY ANTAGONIST?
Another point to consider is that deterioration during
more advanced stages of chronic renal failure often is accompanied by progression to increasingly severe cachexia,
which signals a death trajectory.14 In studies of aging populations across species, 15–19 death generally tends to be associated with more precipitous declines of body mass that are
recognizable around the time that late-life mortality increases. However, factors that influence body composition
before termination may not reflect only secondary, preterminal degenerative processes. The higher percentage of cats with
kidney-related death and thin body condition suggests prior
transition from more obese body condition in at least some
subjects. This observation aligns well with typical clinical observations of an early onset of very gradual change in body
mass in patients that eventually develop renal disease.
Aside from the role of body composition in the death trajectory, serial body composition dual-energy x-ray absorptiometry data from 119 cats over years of healthy adult life resulted
in heritability and principal component outcomes indicating
that multiple genes are involved in phenotypic expression of
healthy body composition in cats. Two heritable principal components, PC2 (h2 = .40, P < .01) and PC6 (h2 = .74, P < .01), explained 24.7% and 1.3% of the population variance,
respectively. The first principal component, PC1, which accounted for 55% of population variance (h2 = .33), was less
strongly significant (P = .038), possibly as a result of the number of variables tested. The observation that terminal body
condition has a quantitative genetic component was unexpected and indicates a need for reevaluation of the underlying role of body composition in “diseases” of aging.
Interestingly, individual components of body composition
related to each other only moderately in the principal component analysis, further suggesting that phenotypic expression
of individual body composition components might result
from multiple underlying genetic and epigenetic mechanisms.
The specific genes involved in control of body composition
and the relative contributions of those genes are presently unknown; slowly progressive, preterminal loss of body mass may
reflect additional plastic genetic programming. In a renal context, death occurs as the apparent outcome of a pathologic
process only at the point of systemic adaptive failure associated with very advanced nephron deletion or (probably more
frequently in domestic cats) by extranephron, extrarenal, or
extrinsic metabolic factors. Whether these putative events
could result from threshold effects is not known at present,
but this seems an attractive hypothesis.
Genetic evaluation did not reveal directly heritable components of renal tubulointerstitial phenotypes in this population, indicating that the phenotypes are either totally
environmental in origin or that they reflect fixed traits (or
both). It is critically important to recognize that aging, although reflecting conserved programming, also remains a
highly plastic process that is subject to interactions with
stress-response phenotypes that may be the actual fixed
traits.20–26 Therefore, measured heritabilities should be modest at best and are not expected in the case of fixed traits. The
possibility of modulating interactions between fixed alleles
and epigenetic influences also is compatible with a working
hypothesis that ultimately may recharacterize the role of overt
disease in aging, centered around an emerging understanding
of the role of genetic–epigenetic interactions.27–32
The ultimate implications of these observations may involve altering approaches to intervention and prevention,
probably with species and breed or strain specificity. It must
be recognized that at least some components of long-term
intrinsic disease (aging) processes likely represent life-preserving adaptations. Nonspecific attempts at entire abolition
of these processes or use of specific interventions that are applied indiscriminately, universally, or based on insensitive
measures may deprive the individual of selected (or convergent) protective mechanisms.
REFERENCES
1. Hoskins JD. Veterinary Pediatrics: Dogs and Cats from Birth to Six Months.
2nd ed. Philadelphia: WB Saunders; 1995.
2. Kraft W. Geriatrics in canine and feline internal medicine. Eur J Med Res
1998;3:31-41.
3. Heininger K. Aging is a deprivation syndrome driven by a germ-soma
conflict. Ageing Res Rev 2002;1:481-536.
4. Heininger K. The deprivation syndrome is the driving force of phylogeny, ontogeny, and oncogeny. Rev Neurosci 2001;12:217-287.
5. Lawler DF, Evans RH, Chase K, et al. The aging feline kidney: a model
mortality antagonist? J Feline Med Surg 2006;8:363-371.
6. Majno G, Joris I. Apoptosis, oncosis, and necrosis: an overview of cell
death. Am J Pathol 1995;146:3-15.
7. Schelling JR, Nkemere N, Kopp JB, Cleveland RP. Fas-dependent fratricidal apoptosis is a mechanism of tubular epithelial cell depletion in
chronic renal failure. Lab Invest 1995;78:813-824.
8. Sawashima K, Mizuno S, Mizuno-Horikawa Y, et al. Expression of αsmooth muscle actin and fibronectin in tubulointerstitial lesions of cats
with chronic renal failure. Am J Vet Res 2000;61:1080-1086.
9. Scott PP. Cats. In: Hafez E, ed. Reproduction and Breeding Techniques for
Laboratory Animals. Philadelphia: Lea & Febiger; 1970:192-208.
10. Lawler DF, Monti KL. Morbidity and mortality in neonatal kittens. Am
J Vet Res 1984;45:1455-1459.
11. Lawler DF, Bebiak DM. Nutrition and management of reproduction in
the cat. Vet Clin North Am 1986;16:495-519.
12. Bredesen DE. The non-existent aging program: how does it work? Aging
Cell 2004;3:255-259.
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13. Mitteldorf J. Ageing selected for its own sake. Evol Ecol Res 2004;6:937-953.
14. Lulich JP, Osborne CA, Polzin DJ. Feline renal failure. Part 1: clinical,
biochemical, and morphological characteristics of renal failure in cats.
Proc ACVIM 1992:571-572.
15. Lesser GT, Deutsch S, Markofsky J. Aging in the rat: longitudinal and
cross-sectional studies of body composition. Am J Physiol 1973;225:
1472-1478.
16. Lesser GT, Deutsch S, Markofsky J. Fat free mass, total body water and
intracellular water in the aged rat. Am J Physiol 1980;238:R82-R90.
17. Kealy RD, Lawler DF, Ballam JM, et al. Influence of diet restriction on
life span and age-related changes in Labrador retrievers. JAVMA
2002;220:1315-1320.
18. Yu BP, Masoro EJ, Murata I, et al. Life span study of SPF Fischer 344
male rats fed ad libitum or restricted diets. Longevity, growth, lean body
mass and disease. J Gerontol 1982;37:130-141.
19. Lawler DF, Evans RH, Larson BT, et al. Influence of lifetime food restriction on causes, time, and predictors of death in dogs. JAVMA
2005;226:225-231.
20. Clare MJ, Luckinbill LS. The effects of gene-environment interaction on
the expression of longevity. Heredity 1985;55:19-26.
21. Finch CE. Longevity, Senescence and the Genome. Chicago: University of
Chicago Press; 1990.
22. Buck S, Nicholson M, Dudas S, et al. Larval regulation of adult longevity
in a genetically-selected long-lived strain of Drosophila. Heredity
1993;71:23-32.
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Proceedings, 2007 Nestlé Purina Nutrition Forum
23. Scheiner SM. Genetics and evolution of phenotypic plasticity. Annu Rev
Ecol Syst 1993;24:35-68.
24. Finch CE. Comparative perspectives on plasticity in human aging and
life spans: between Zeus and the salmon. In: Wachter KW, Finch CE,
eds. The Biodemography of Longevity. Washington, DC: National Academy Press; 1997:439-454.
25. Krebs RA, Loeschcke V. A genetic analysis of the relationship between
life-history variation and heat-shock tolerance in Drosophila buzzatii.
Heredity 1999;83:46-53.
26. Martin GM. Epigenetic drift in aging identical twins. Proc Natl Acad Sci
USA 2005;102:10413-10414.
27. Jazwinski SM, Kim S, Lai CY, Benguria A. Epigenetic stratification: the
role of individual change in the biological aging process. Exp Gerontol
1998;33:571-580.
28. Robert L, Labat-Robert J. Aging of connective tissues; from genetic to
epigenetic mechanisms. Biogerontology 2000;1:123-131.
29. Feinberg AP, Oshimura M, Barrett JC. Epigenetic mechanisms in human
disease. Cancer Res 2000;62:6784-6787.
30. Issa JP. Epigenetic variation and human disease. J Nutr 2002;
132(suppl):2388-2392.
31. Claus R, Lubbert M. Epigenetic targets in hematopoietic malignancies.
Oncogene 2003;22:6489-6496.
32. Kopelovich L, Crowell JA, Fay JR. The epigenome as a target for cancer
chemoprevention. J Natl Cancer Inst 2003;95:1747-1751.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
What Is Different about Chronic Kidney
Disease in Cats?
David J. Polzin, DVM, PhD, DACVIM
College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota
Kidney disease is defined as the presence of functional or structural abnormalities in one or both kidneys; chronic kidney disease (CKD) is defined as kidney disease that exists for at least
3 months.1 CKD is the most common kidney disease in cats. As
with most species, CKD is primarily a disease of older cats. One
recent publication estimated the prevalence of CKD among
cats of all ages to be 112 cases per 1,000 cats.2 Among cats 10
years of age and older, prevalence was estimated to be 269
cases per 1,000, while the prevalence in cats 15 years of age
and older was 491 per 1,000.2 CKD appears to be two to three
times more prevalent in cats than in dogs1; the reason for this
is unknown. Although CKD is an irreversible and progressive
condition, most affected cats survive for several months to
years, and many ultimately die of conditions other than CKD.
RECOGNITION AND STAGING
Although CKD may be recognized initially via physical examination, serum biochemistries, urinalysis, or imaging studies, it is most commonly detected as reduced renal function
(azotemia). Differentiating renal azotemia from prerenal
azotemia is usually based on examining urine concentration
concurrent with detection of azotemia. Because cats tend to
have an exceptional ability to concentrate their urine, it is not
surprising that cats, compared with dogs or humans, typically
maintain a greater degree of urine concentrating ability as
renal function declines. As a consequence, less advanced CKD
may be associated with relatively concentrated urine in some
cats. Absent other causes for dilute urine (e.g., hyperthyroidism, diabetes mellitus), serum creatinine values of 1.6
mg/dl or greater associated with urine specific gravity values
less than 1.035 should generally be interpreted as consistent
with renal azotemia.1 Cats with more advanced CKD typically have urine specific gravity values below 1.020. Urine
specific gravity values between 1.035 and 1.040 constitute a
“gray zone” in which azotemia may be renal or prerenal;
however, cats may occasionally present a diagnostic dilemma
because they remain persistently azotemic for months to
years with urine specific gravity values greater than 1.040.
These cats most likely have CKD.
To facilitate application of appropriate clinical practice
guidelines for diagnosis and treatment, patients with CKD
are categorized into four stages along a continuum of progressive kidney disease.1 (For more information on staging
chronic kidney disease, visit the International Renal Interest
Society website at www.iris-kidney.org.) The stage of CKD is
assigned based on the level of kidney function ascertained by
two or more determinations of serum creatinine concentration obtained while the patient is well hydrated:
•
•
•
•
Stage 1: Serum creatinine <1.6 mg/dl
Stage 2: Serum creatinine 1.6–2.8 mg/dl
Stage 3: Serum creatinine 2.9–5.0 mg/dl
Stage 4: Serum creatinine >5.0 mg/dl
The stage is further elucidated by proteinuria status and the presence of systemic hypertension because these factors appear to
influence prognosis and are amenable to therapeutic modification. Cats with urine protein:creatinine ratios less than 0.2 are
classified as nonproteinuric, ratios between 0.2 and 0.4 indicate
borderline proteinuria, and ratios greater than 0.4 indicate proteinuria. Cats with systolic blood pressure less than 150 mm Hg
are considered to have minimal risk of experiencing hypertensive end-organ injuries (e.g., renal, ocular, cardiac, or nervous
system lesions). Cats with systolic blood pressure between 150
and 159 mm Hg, 160 and 179 mm Hg, or greater than 180 mm
Hg are considered to have a low, moderate, or high risk, respectively, of experiencing hypertensive end-organ injuries.
CAUSE AND PATHOLOGY
CKD in cats may be initiated by a variety of familial, congenital, or acquired diseases. Unfortunately, the initiating cause(s)
of CKD often cannot be identified at the time of diagnosis. In
one study, chronic tubulointerstitial nephritis was observed
in 70% of cats with CKD, whereas glomerulonephropathy occurred in 15%, lymphoma in 11%, amyloidosis in 2%, and
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tubulonephrosis in 2%.3 The prevalence of nonproteinuric
tubulointerstitial disease appears to be greater in cats than in
dogs or humans. Unfortunately, the histologic diagnosis of
tubulointerstitial nephritis does not help to identify the underlying cause of kidney disease and probably represents the
final common pathway for progression of many feline renal
diseases. The initiating causes of diseases believed to originate
in the tubulointerstitium have been especially elusive; however, one possible cause for the higher prevalence of CKD in
cats has recently been proposed. Subcutaneous administration in kittens of feline herpesvirus 1, calicivirus, and panleukopenia virus vaccines grown in feline tissue culture
systems has been shown to induce production of antifeline
renal tissue antibodies in serum and a tubulointerstitial inflammatory response within the renal tubulointerstitium.4
This observation prompts the question of whether repeated
vaccinations play a role in the development of CKD in cats.
Another interesting observation that appears to be unique to
cats is the high frequency of nephroliths and ureteroliths in
those with CKD. These uroliths are composed predominantly
of calcium oxalate. The origin of these uroliths and whether they
develop before, during, or after the onset of CKD are not known.
Although ureteroliths have become an important cause of acute
uremic crises in cats, the presence of nephroliths does not appear
to adversely affect clinical outcomes in cats with CKD.5 Although
it may be necessary to surgically remove ureteroliths associated
with complete, persistent ureteral obstruction, removal of
nephroliths is generally not recommended.
BIOLOGIC BEHAVIOR
A progressive decline in kidney function over months to
years is typical of naturally occurring CKD.1,6 Although it is
logical to assume that CKD progresses as a consequence of
ongoing renal injury associated with the disease process that
initiated kidney disease, the initiating cause for CKD cannot
be identified at the time of diagnosis in most patients. The
preponderance of clinical and experimental evidence suggests that in dogs and cats with stages 3 and 4 CKD, progressive loss of kidney function results, at least in part, from
factors unrelated to the inciting disease.1,6 These factors may
include intraglomerular hypertension, glomerular hypertrophy, hypertension, proteinuria, intrarenal precipitation of
calcium phosphate, and tubulointerstitial disease.
Whereas progression of CKD in humans and dogs is often
characterized by a linear pattern of decline in glomerular filtration rate (GFR), progression of CKD in cats more com42
Proceedings, 2007 Nestlé Purina Nutrition Forum
monly appears as abrupt, usually unpredictable, increases in
serum creatinine concentration.2 In a clinical trial performed
at the University of Minnesota, renal function as measured
by serum creatinine remained stable for up to 24 months in
40 of 45 cats.7 Five of the 45 cats developed uremic crises associated with abrupt increases in serum creatinine concentrations after having had stable renal function for 3 to 21
months. Upon retrospective evaluation of the clinical data on
these cats, no clear indicators were found to be useful in predicting an impending decline in kidney function.
The seeming stability of renal function in many cats with
CKD translates into relatively long survival time. Compared
with dogs having similar levels of renal dysfunction, cats typically live many months or years longer. In fact, many older
cats succumb to other diseases before their CKD becomes severe enough to cause significant morbidity.
MODIFYING CLINICAL OUTCOMES
Even though feline CKD tends to be generally less progressive
than CKD in dogs, many cats still progress to a point where it becomes difficult or impossible to have a satisfactory quality of
life. Recent studies have indicated that certain medical interventions may delay or prevent progression of CKD, thereby extending survival with a good quality of life. Factors that have
been shown to influence survival times for cats with CKD include the severity of reduction in GFR (stage of CKD) and magnitude of proteinuria. There may also be an interaction between
systemic hypertension and proteinuria on survival. With greater
severity of intrinsic renal dysfunction or magnitude of proteinuria, shorter survival time is likely. Some other factors that may
or may not influence progression of CKD directly include systemic hypertension, pyelonephritis, and presence of nephroliths.
All patients with CKD are potentially at risk for progressive
kidney disease. Progression may occur as a consequence of
the primary renal disease, in association with a variety of secondary factors that may promote progressive renal disease,
or both. An important therapeutic goal for managing patients
with CKD is to minimize or prevent progressive loss of renal
function. Treatment designed to limit progression of kidney
disease may involve a variety of interventions, including diet
therapy, minimizing proteinuria, controlling hypertension,
and modulating the renin-angiotensin-aldosterone system.
There is substantial clinical trial evidence supporting the
effectiveness of dietary intervention in prolonging survival of
cats with CKD; there is no credible clinical evidence to the
contrary. In a nonrandomized clinical trial, cats fed a renal
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WHAT IS DIFFERENT ABOUT CHRONIC KIDNEY DISEASE IN CATS?
diet survived significantly longer than cats that continued to
consume their usual diet (633 versus 264 days).8 It was not
possible to detail the differences between the diets used in this
study, but the therapeutic renal diet had a reduced protein and
phosphorus content. The renal diet was shown to be beneficial in lowering serum phosphorus and parathyroid hormone
concentrations, and it was suggested that the beneficial effect
of the diet may have been related to this effect.9 A randomized, controlled clinical trial from the University of Minnesota
Veterinary Medical Center further confirmed the beneficial effects of diet therapy in prolonging survival of cats with CKD.7
In this study, the effect of a renal diet on survival was compared with that of a maintenance diet in 45 cats with spontaneous CKD. Renal-related mortality in 23 cats fed an adult
maintenance diet was 17.4%, whereas no deaths were observed in 22 cats fed the renal diet, which was restricted in protein and phosphorus content. In a retrospective study of cats
with CKD treated at 31 veterinary clinics in the Netherlands,
feeding a renal diet compared with a typical feline diet was
found to be associated with a significant increase in median
survival time (7 months among cats consuming conventional
cat foods; 16 months for cats consuming a renal diet).10
A common misconception is that renal diets are simply
low-protein diets. Renal diets encompass a variety of modifications beyond just a limitation of protein content, and, indeed, the principal beneficial effects of these diets may not
accrue from their reduction in protein content. Thus, simply
replacing a renal diet with a standard manufactured diet that
is lower in protein content does not meet the guideline for
feeding a renal diet. Because inappropriate diets can exacerbate clinical signs of uremia or promote progression of CKD,
cats with CKD should be fed a renal diet.
Treatments designed to reduce glomerular proteinuria are
recommended for managing proteinuric cats with CKD stages
1 through 4. Intervention is indicated when the urine protein:creatinine ratio exceeds 2.0 in cats with CKD stage 1 and
0.4 in cats with CKD stages 2 through 4.11 Proteinuria has been
shown to adversely affect outcome in humans, dogs, and cats
with CKD, presumably because proteinuria itself appears to injure the renal tubules, thereby promoting progression of CKD.
It is well established in human patients that reducing proteinuria by suppressing the renin-angiotensin-aldosterone system
ameliorates the adverse effects of proteinuria on the kidneys.12
While qualitatively similar, evidence in cats is less compelling.
Although studies have shown that proteinuria is closely linked
to progression of CKD in cats and that angiotensin-converting
enzyme (ACE) inhibitors are effective in reducing proteinuria in
cats with CKD,13 the effectiveness of ACE inhibitor therapy in altering the course of CKD in cats remains to be confirmed.14,15
Nevertheless, ACE inhibitors such as benazepril and enalapril
are recommended for patients with CKD that meet the above
criteria. Interestingly, treatment of systemic hypertension in cats
with CKD using amlodipine besylate has been shown to be associated with a reduction in the magnitude of proteinuria.16
Ideally, therapy should be adjusted so that the urine protein:creatinine ratio is reduced to 0.4 or lower; however, this
may be difficult or impossible in many patients and may require higher doses of ACE inhibitors or the addition of angiotensin II receptor-blocking drugs (e.g., losartan, irbesartan).
REFERENCES
1. Polzin DJ, Osborne CA, Ross S. Chronic kidney disease. In: Ettinger SJ,
Feldman E, eds. Textbook of Veterinary Internal Medicine. St. Louis: Elsevier Saunders; 2005:1756-1785.
2. Ross SJ, Polzin DJ, Osborne CA. Clinical progression of early chronic renal
failure and implications for management. In: August J, ed. Consultations in
Feline Internal Medicine. St. Louis: Elsevier Saunders; 2005:389-398.
3. Minkus G, Horauf A. Evaluation of renal biopsies in cats and small
dogs: histopathology in comparison with clinical data. J Small Anim
Pract 1994;35:465-472.
4. Lappin MR, Basaraba RJ, Jensen WA. Interstitial nephritis in cats inoculated with Crandell Rees feline kidney cell lysates. J Feline Med Surg
2006;8:353-356.
5. Ross SJ, Osborne CA, Lekcharoensuk C, et al. A case-control study of
the effects of nephrolithiasis in cats with chronic kidney disease. JAVMA
2007;230:1854-1859.
6. Brown S, Crowell W, Brown C, et al. Pathophysiology and management
of progressive renal disease. Vet J 1997;154:93-109.
7. Ross SJ, Osborne CA, Kirk CA, et al. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats.
JAVMA 2006;229:949-957.
8. Elliot J, Rawlings J, Markwell P, et al. Survival of cats with naturally occurring chronic renal failure: effect of dietary management. J Small Anim
Pract 2000;41:235-242.
9. Barber P, Rawlings J, Markwell P, et al. Effect of dietary phosphate restriction on renal secondary hyperparathyroidism in the cat. J Small
Anim Pract 1999;40:62-70.
10. Plantinga EA, Everts H, Kastelein AMC, et al. Retrospective study of the
survival of cats with acquired chronic renal insufficiency offered different commercial diets. Vet Rec 2005;157:185-187.
11. Lees GE, Brown SA, Elliott J, et al. Assessment and management of proteinuria in dogs and cats: 2004 ACVIM Forum Consensus Statement
(Small Animal). J Vet Intern Med 2005;19:377-385.
12. Abbate M, Zoja C, Remuzzi G. How does proteinuria cause progressive
renal damage? J Am Soc Nephrol 2006;17:2974-2984.
13. Syme HM, Markwell PJ, Pfeiffer D, et al. Survival of cats with naturally
occurring chronic renal failure is related to severity of proteinuria. J Vet
Intern Med 2006;20:528-535.
14. Mizutani H, Koyama H, Watanabe T, et al. Evaluation of the clinical efficacy of benazepril in the treatment of chronic renal insufficiency in
cats. J Vet Intern Med 2006;20:1074-1079.
15. King JN, Gunn-Moore DA, Tasker S, et al. Tolerability and efficacy of
benazepril in cats with chronic kidney disease. J Vet Intern Med 2006;20:
1054-1064.
16. Jepson RE, Elliott J, Brodbelt D, et al. Effect of control of systolic blood
pressure on survival in cats with systemic hypertension. J Vet Intern Med
2007;21:402-409.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Feline Urolithiasis: Understanding the
Shift in Urolith Type
Jody P. Lulich, DVM, PhD, and Carl A. Osborne, DVM, PhD
College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota
Naturally occurring urolithiasis is affected by many known
and unknown risk factors. Known risk factors that influence
urolith formation include diet, urine pH, water homeostasis,
breed, abnormalities of metabolism, urinary tract infection
(UTI), and anatomic and functional abnormalities of the urinary tract. Each factor may play a significant or limited role
in the development or prevention of different types of
uroliths. Recognition and control of lithogenic risk factors is
the primary goal to prevent urolith formation and minimize
urolith recurrence.
The Minnesota Urolith Center has performed quantitative
analysis of uroliths from cats for more than two decades. During this period, we have observed substantial shifts in urolith
type (Figure 1). In 1981, struvite was the most common
stone, representing 78% of urolith submissions. A decade
later, struvite remained the most common stone; however, its
prevalence had declined to 59%. By the end of the second
decade, the ever-present struvite had been supplanted by the
emergence of calcium oxalate (CaOx). In 2001, uroliths were
retrieved from 6,185 cats and submitted for quantitative
analysis; 55% were CaOx, and 34% were struvite. Epidemiologic shifts in feline urolith type were not confined to the
United States: Increased prevalence of CaOx was also observed in Asia and Europe. Because of the short time span in
which this occurred, we hypothesized that changes in husbandry and nutrition represent significant contributing factors influencing this epidemiologic shift in urolith type.
THE RISE AND DECLINE OF STRUVITE
In the early 1970s, the association between dry diets and feline lower urinary tract disease (fLUTD) became a topic of intense discussion in England, Denmark, and the United States.
Also in the early 1970s and continuing for the next decade,
several groups of investigators experimentally produced magnesium hydrogen phosphate and then magnesium ammonium phosphate (MAP) uroliths in clinically normal cats by
adding various types of magnesium salts to their diets.1,2 The
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Proceedings, 2007 Nestlé Purina Nutrition Forum
cats developed typical signs of fLUTD, including urethral obstruction, but they did not produce the struvite-matrix urethral plugs commonly encountered in cats with naturally
occurring urethral obstruction. The general consensus of
many investigators and clinicians was that consumption of
dry diets with excessive magnesium was an important primary cause of fLUTD.
Following the development of dietary protocols to induce
dissolution of naturally occurring struvite uroliths in dogs,
dietary protocols to dissolve naturally occurring sterile struvite urocystoliths in cats emerged in 1983.3 Their effectiveness justified the emphasis on dietary factors in the
prevention of sterile struvite urolithiasis.
In 1985, the results of studies on the effects of feeding
diets containing alkalinizing and acidifying salts of magnesium to clinically normal cats were reported.4 These laboratory studies shifted the focus from dietary magnesium
content to alkaline urine pH as a primary factor in the development of struvite crystalluria. Results of these studies
had a profound effect on veterinarians and the pet food industry. Many adult feline maintenance diets were eventually
modified to minimize struvite crystalluria. Because of dietary modifications, the prevalence of struvite uroliths and
struvite urethral plugs began to decline in the mid-1980s.
Unexpectedly, the decrease in prevalence of struvite-related
urolithiasis was associated with a concomitant increase in
the prevalence of CaOx urolithiasis even though struvite remained the primary mineral component of urethral plugs.
THE EMERGENCE OF CALCIUM OXALATE
The exact etiologic cascade of events that led to the increased
prevalence of CaOx uroliths remains unknown. However,
several biologic phenomena provide plausible explanations.
The Role of Diet
Results of epidemiologic studies support the hypothesis that
diets designed to minimize MAP urolith formation may have
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FELINE UROLITHIASIS: UNDERSTANDING THE SHIFT IN UROLITH TYPE
Percent
inadvertently increased the occurrence of
CaOx uroliths.5,6 Whereas diet-mediated
100
% CaOx
urine acidification enhances the solubility of
% MAP
MAP crystals in urine, dietary acids promote
80
CaOx crystalluria by inducing hypercalciuria.
This association between aciduria, acidemia,
60
and hypercalciuria may be explained by the
fact that acidemia promotes mobilization of
40
carbonate and phosphate from bone to
buffer hydrogen ions. Concomitant mobi20
lization of bone calcium may result in hy0
percalciuria. In addition, metabolic acidosis
81 83 85 87 89 91 93 95 97 99 01 03 05
in dogs, humans, and rats may result in
Year
hypocitraturia. If consumption of dietary
acid precursors is associated with hypocitraFigure 1. The yearly percentage of feline uroliths composed of CaOx compared with
turia in cats, it may increase the risk of CaOx those composed of MAP (Minnesota Urolith Center; n = 83,601 submissions).
uroliths because citrate is an inhibitor of
CaOx crystal formation.
Over the past 50 years, the incidence of CaOx uroliths in
CaOx uroliths are uncommon in immature cats in which
humans living in the United States has increased considerurine is normally acidic. The answer is likely related to a com7
ably. Global distribution of urolithiasis in humans indicates
bination of risk factors associated with CaOx urolithiasis, inthat CaOx uroliths predominate in the United States and
cluding the concentrations of minerals and nonmineral
other industrialized, technologically advanced regions of the
crystallization inhibitors and promoters and the quantity of
world.8 Although originally attributed to the sedentary
urine produced. There likely is no simple cause-and-effect re8
lifestyle of inhabitants of such countries, the increased incilationship between a single risk factor and CaOx urolithiasis.
dence of CaOx uroliths is now believed to reflect the ability
Why MAP has remained the most common mineral of
of these more affluent societies to spend disposable income
urethral plugs while the prevalence of feline CaOx has drafor the consumption of animal protein, which leads to inmatically increased in uroliths is unknown. However, the obcreased urinary excretion of acidic metabolites, calcium, and
servation that the average age of cats with urethral plugs is
oxalate.9,10 Regional environmental factors, such as water and
lower (approximately 2 to 4 years old) than that of cats with
soil quality, may also influence urolith formation. It is logiCaOx uroliths leads to the hypothesis that age-related
cal to consider that variables that contribute to the increased
changes in urine promoters for urolithiasis play an imporincidence of CaOx uroliths in humans may also influence the
tant role. As an illustration, in a case-control study comparincidence of CaOx uroliths in cats. In other words, are strateing the age of 7,895 cats with CaOx uroliths that were
gies that incorporate the concepts of improved nutrition or
submitted to the Minnesota Urolith Center between 1981
overnutrition a risk factor for CaOx urolith formation?
and 1997 with the age of 150,482 cats admitted to veterinary
colleges in North America, cats at greatest risk of developing
The Role of Age
CaOx uroliths were those between 7 and 10 years of age.11
In a retrospective study of feline CaOx uroliths from 922 cats,
Cats in this age group were 67 times more likely to form
only 3 were younger than 1 year of age. Ninety-seven percent
uroliths than cats 1 to 2 years of age. The mean age of cats
of affected cats were older than 2 years. These observations
with CaOx uroliths was 7.5 ± 3.3 years. In contrast, cats at
are interesting because conditions promoting urine acidity
highest risk of developing MAP uroliths were between 4 and
have been identified as a risk factor for CaOx urolith forma7 years of age. These comparisons are clinically important betion, and the urine pH of young cats is lower than that of
cause they emphasize the need to monitor cats receiving diets
adult cats consuming the same diet. If acidic urine is an imthat promote urine acidification because as cats get older, the
portant risk factor for CaOx, a reasonable question is why
risk of developing CaOx urolithiasis increases.
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The Role of Oxalobacter spp
Hyperoxaluria is an important risk factor for CaOx urolith formation. Although the majority of urinary oxalate is derived
from endogenous metabolic pathways, increased urinary oxalate appears to be sustained by increased dietary load and increased intestinal absorption. Studies in rats have demonstrated
that components of the intestinal microflora, particularly Oxalobacter formigenes, use oxalate in the gut, thus limiting its absorption.12 Of particular interest is the observation that human
patients with recurrent UTIs excrete higher quantities of oxalate
than do stone formers without UTIs.13 It was hypothesized that
antibiotic control of UTIs reduces intestinal Oxalobacter populations. Conceptually, this association may be important for
two reasons: (1) antibiotics are commonly used in the management of idiopathic fLUTD and (2) renal tubular damage by
increased urine oxalate concentrations may serve as a nidus for
crystal nucleation, adherence, and growth.
THE AGE OF NEPHROURETEROLITHIASIS
The increase in occurrence of CaOx uroliths in cats has been
associated with a parallel increase in occurrence of CaOx
uroliths found in their kidneys and ureters. In fact, there has
been a 10-fold increase in the frequency of upper tract
uroliths diagnosed in cats evaluated at veterinary teaching
hospitals in North America over the past 20 years.14
Between 1981 and 2003, the Minnesota Urolith Center analyzed nephroureteroliths from 1,599 cats. Seventy percent of
the uroliths were composed of CaOx. In contrast, only 8%
were composed of MAP. While enrolling cats with renal failure into a clinical trial, we were surprised to find that 48% had
radiographic evidence of nephroliths or ureteroliths. This finding emphasizes the importance of CaOx prevention and control in cats to minimize potential life-threatening renal failure.
Is kidney disease a cause or a consequence of urolith formation? Hyperoxaluria may be the common link between
these two processes. One current hypothesis proposes that
excessive oxalate damages kidney tubules.15 The damaged
tubules become mineralized (Randall’s plaques, which are
sites of interstitial mineralization at or near the renal papilla
found in kidneys of CaOx stone formers) and serve as a nidus
for CaOx precipitation (epitaxy). By increasing urine saturation, hyperoxaluria also promotes precipitation of calcium. In
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Proceedings, 2007 Nestlé Purina Nutrition Forum
turn, CaOx uroliths of sufficient size can block the ureter,
promoting kidney failure.
THE EPOCH OF HOPE
Since 2001, the Minnesota Urolith Center has observed a consistent decline in the yearly percentage of cats with CaOx
uroliths (Figure 1). Although factors other than a change in
the occurrence of CaOx may contribute to this reduction, we
have taken the optimistic perspective that increased knowledge and understanding of the risk factors associated with
CaOx formation have favorably altered husbandry, nutrition,
and veterinary care.
REFERENCES
1. Lewis LD, Chow FHC, Taton GF, Hamar DW. Effects of various dietary
mineral concentrations on the occurrence of feline urolithiasis. JAVMA
1978;172:559-563.
2. Rich LJ, Dysart I, Chow FHC, Hamar D. Urethral obstruction in male
cats: experimental production by addition of magnesium and phosphate to the diet. Feline Pract 1974;4:44-47.
3. Osborne CA, Lulich JP, Kruger JM, et al. Medical dissolution of feline
struvite urocystoliths. JAVMA 1990;196:1053-1063.
4. Buffington CA, Rogers QR, Morris JG. Feline struvite urolithiasis: magnesium effect depends on urinary pH. Feline Pract 1985;15:29-33.
5. Lekcharoensuk C, Osborne CA, Lulich JP, et al. Association between dietary factors and calcium oxalate and magnesium ammonium phosphate uroliths in cats. JAVMA 2001;219:1228-1237.
6. Kirk CA, Ling GV, Franti CE, Scarletti JM. Evaluation of factors associated with development of calcium oxalate urolithiasis in cats. JAVMA
1995;207:1429-1434.
7. Mandel NS, Mandel GS, Urinary tract stone disease in the United States
veteran population II: geographical analysis of variations in composition. J Urol 1989;1432:11516-11521.
8. Lonsdale K. Human stones. Science 1968;159:199-1207.
9. Robertson WG, Peacock M, Hodgkinson A. Dietary changes and the incidence of urinary calculi in the UK between 1958 and 1976. J Chronic
Dis 1979;32:469-476.
10. Robertson WG, Peacock M, Heyburn PJ. Should recurrent calcium oxalate stone formers become vegetarians? Br J Urol 1979;51:427-431.
11. Lekcharoensuk C, Osborne CA, Lulich JP. The epidemiology of feline
lower urinary tract disease: patient risk factors, 1980–1997. JAVMA
2001;218:1429-1435.
12. Sidhu H, Allison MJ, Chow JM, et al. Rapid reversal of hyperoxaluria in
a rat model after probiotic administration of Oxalobacter formigenes. J
Urol 2001;166:1487-1491.
13. Hoppe B, Von Unruh G, Laube N, et al. Oxalate degrading bacteria: new
treatment option for patients with primary and secondary hyperoxaluria. Urol Res 2005;33:372-375.
14. Lekcharoensuk C, Osborne CA, Lulich JP, et al. Trends in the frequency
of calcium oxalate uroliths in the upper urinary tract of cats. JAAHA
2005;41:39-46
15. Turan T, Tuncay OL, Usubutun A, et al. Renal tubular apoptosis after
complete ureteral obstruction in the presence of hyperoxaluria. Urol Res
2000;28:220-222.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
In Search of the Origins of Feline Hyperthyroidism
Deborah S. Greco, DVM, PhD, DACVIM
Nestlé Purina PetCare, St. Louis, Missouri
Feline hyperthyroidism was first described in 1979 and 1980
by investigators in New York and Boston, respectively.1,2 The
question at that time and ever since has been, “Is hyperthyroidism a new disease in cats?” Based on epidemiologic and
hospital-acquired data, the answer appears to be “yes.” During a 14-year period (1970 to 1984), an average of 1.9 cats per
year were diagnosed with hyperthyroidism; however, it is now
estimated that the incidence is as high as 2% of the feline
population seen in tertiary care veterinary facilities.3,4 Hyperthyroidism has become the most frequently diagnosed endocrinopathy in cats, with reports originating from North
America, Europe (especially the United Kingdom), New
Zealand, and Australia. Hyperthyroidism in cats has become
increasingly more prevalent as a result of an increase in the
number of cats that survive past 10 years of age, improved diagnostics, and increased suspicion of the disease among veterinarians. Dozens of studies have been published on the
origins of feline hyperthyroidism, but none provides a definitive answer to the mystery behind this disease.
THYROID PHYSIOLOGY
The thyroid gland is the most important endocrine gland for
metabolic regulation. The synthesis of thyroid hormone is unusual because a large amount of the active hormone is stored as
a colloid within the lumen or acinus, created by the circular
arrangement of glandular cells. Two molecules— tyrosine and
iodine—are important for thyroid hormone synthesis. Tyrosine
is a part of thyroglobulin, a large molecule (molecular weight:
660,000 D) formed within the follicle cell and secreted into the
lumen of the follicle. Iodine is converted to iodide in the intestinal tract and then transported to the thyroid, where the follicle cells effectively trap the iodide through an active transport
process. This allows intracellular iodide concentrations to be
25 to 200 times higher than extracellular concentrations.
As iodide passes through the apical wall of the cell, it attaches to the ring structures of the tyrosine molecules, which
are part of the thyroglobulin amino acid sequence. The tyrosyl ring can accommodate two iodide molecules; if one iodide
molecule attaches, it is called monoiodotyrosine, and if two at-
tach, it is called diiodotyrosine. The coupling of two iodinated
tyrosine molecules results in the formation of the main
thyroid hormones: two diiodotyrosine molecules form
tetraiodothyronine (T4), and one monoiodotyrosine and one
diiodotyrosine molecule form triiodothyronine (T3). Thyroperoxidase, a key enzyme in the biosynthesis of thyroid hormones, works in concert with an oxidant, hydrogen peroxide.
Thyroperoxidase catalyzes the iodination of the tyrosyl
residues of thyroxine-binding globulin and the formation of
T3 and T4. In addition to the unusual molecular storage form
of the hormone, thyroid hormones are also unique in that
they are the only hormones that contain a halide (i.e., iodine).
The main form of metabolism of thyroid hormones involves the removal of iodide molecules. The two enzymes involved in T3 and reverse T3 synthesis, 5′-deiodinase and
5-deiodinase, are also involved in the catabolism of thyroid
hormones. The majority of T3 formation occurs outside the
thyroid gland by deiodination of T4. The enzyme involved in
the removal of iodide from the outer phenolic ring of T4 in
the formation of T3 is called 5′-monodeiodinase. Another type
of T3 in which an iodide molecule is removed from the inner
phenolic ring of T4, a compound called reverse T3, is also
formed. Reverse T3 has little of the biologic effects of thyroid
hormones and is formed only by the action of extrathyroidal
deiodinating enzymes, not by activity of the thyroid.
CLINICAL ASPECTS OF HYPERTHYROIDISM
As noted, hyperthyroidism is the most common endocrinopathy of cats. It is caused by adenomatous hyperplasia of the thyroid gland. Middle-aged to older cats are
typically affected, and there is no predilection for breed or
sex, although some studies suggest a male predilection and a
decreased incidence in Himalayans and Siamese.5
Hyperthyroidism is characterized by hypermetabolism;
therefore, polyphagia, weight loss, polydipsia, and polyuria
are the most prominent features of the disease. Activation of
the sympathetic nervous system is also seen. Hyperactivity,
tachycardia, pupillary dilatation, and behavioral changes are
characteristic of the disease in cats. Long-standing hyperthy-
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roidism leads to hypertrophic cardiomyopathy, high-output
heart failure, and cachexia, all of which may lead to death.
Feline hyperthyroidism is diagnosed by measuring total T4
(TT4); total T3 measurement is generally noncontributory to a
diagnosis. Because the disease has become more common and
recognized in its early stages, free T4 (FT4) concentrations have
been shown to be more diagnostic of early or “occult” hyperthyroidism; however, FT4 concentrations should be interpreted
in light of TT4 because nonthyroidal illness (e.g., chronic renal
failure) can result in spurious elevations of FT4 as well.
NUTRITIONAL ASPECTS OF
HYPERTHYROIDISM
An inability to secrete adequate amounts of thyroid hormone
often leads to the enlargement of the thyroid gland, a condition known as goiter. In many places around the world, this
condition is, or has been, caused by a deficiency of iodine in
the diet, a situation that has largely been corrected through
the use of iodized salt. Balanced pet foods provide sufficient
iodine but vary widely in iodine content.6 The effects of this
variation have been theorized to be important in cats, but
there are no data to support or refute the theory. Tartellin et
al7 showed an acute inverse relationship between FT4 and dietary iodine in cats fed low- and high-iodine diets for 2
weeks; however, a subsequent study concluded that no effect
on serum TT4 or FT4 was seen when the cats were fed low- or
high-iodine diets for more than 5 months.8 Chronic changes
in dietary iodide are associated with “adaptation” of the thyroid gland and are therefore unlikely to be the cause of feline
hyperthyroidism. One study showed that feeding a low-iodine diet to cats with preexisting hyperthyroidism failed to
affect high concentrations of circulating thyroid hormone.3,9
Certain plants (e.g., cruciferous plants such as cabbage,
kale, rutabaga, turnip, and rapeseed) contain a potent antithyroid compound called progoitrin, which is converted into
goitrin within the digestive tract. Goitrin interferes with the
organic binding of iodine. Many of the goitrogenic feeds also
contain thiocyanates, which interfere with the trapping of iodine by the thyroid gland. Increasing the amount of iodine
consumed can sometimes overcome the effects of thiocyanate
but has less influence on overcoming the effects of goitrin.
Goitrogens can result in hypothyroidism, and some have theorized that chronic exposure to goitrogens can lead to toxic
nodular goiter, resulting in hyperthyroidism.
It has been theorized that flavinoids from soy proteins play
a role in the pathogenesis of hyperthyroidism in cats.
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Proceedings, 2007 Nestlé Purina Nutrition Forum
Quercetin, a flavinoid, is capable of stimulating mitogenesis
in a cell-culture line from hyperthyroid cats.10 Polyphenolic soy
isoflavones, such as genistein and daidzein, were identified in
almost 60% of dry cat foods tested.11 Some dry foods contain
isoflavone at levels consistent with those shown to interfere
with thyroid function by inhibiting thyroperoxidase in rats and
5′-deiodinase activity in cats12,13; however, these cell-culture
and in vitro studies are in contradiction to epidemiologic data
that show hyperthyroidism to be less common in cats fed dry
foods.4,5,14 Studies in rats have demonstrated in vitro effects of
soy isoflavones, especially in conjunction with iodine deficiency; however, an in vivo effect on TT4 and thyroid-stimulating hormone (TSH) has not been observed.12,15 In a prospective
study of 18 clinically normal cats eating a soy diet (400 mg
isoflavones/kg diet), TT4 and FT4 concentrations were significantly, but modestly, increased, whereas T3 concentrations were
unchanged.13 Many human studies have shown no detrimental effect of soy isoflavones on thyroid function, particularly
when incorporated into a balanced diet with adequate iodine
intake.16,17 Thus, the effect of soy, if any, within complete cat
foods remains controversial.
Although unproven, canned cat food has been implicated
as a cause of feline hyperthyroidism in multiple epidemiologic studies.4,5,14 The suspected goitrogen is bisphenol A diglycidyl ether (BADGE), a substance used in the manufacture of
the liners of easy-open pop-top cans. It is suspected that this
compound can leach into food and be consumed by cats.
While this BADGE-based lining is generally considered safe
and is used with foods for human consumption, it is suggested that cats may be more susceptible to toxic effects of this
compound because they have a greatly reduced ability to
detoxify it via hepatic glucuronidation. At toxic levels, bisphenol A also reduces triiodothyronine binding and causes increased TSH secretion, resulting in hyperthyroidism and goiter
in rats and some humans. On the other hand, although cat
studies may not be available, rodent studies show a very high
safety margin.18 It also should be noted that epidemiologic
studies showing associations are not the same as cause and
effect. Over 90% of cats in the United States consume commercial pet foods as their primary nutritional source, and relatively few develop hyperthyroidism.
IMMUNOLOGIC ASPECTS OF
HYPERTHYROIDISM
The literature regarding an immunologic cause of hyperthyroidism is contradictory. Initially, feline hyperthyroidism was
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IN SEARCH OF THE ORIGINS OF FELINE HYPERTHYROIDISM
believed to be similar to Grave’s disease in humans.19 In fact,
the clinical signs of hypermetabolism associated with feline
hyperthyroidism are identical to Grave’s disease; however,
several studies have shown that, unlike Grave’s disease, which
is caused by autoantibodies to the thyroid TSH receptor, cats
with hyperthyroidism have antibodies that do not stimulate
the TSH receptor.20 In other research, antibodies from hyperthyroid cats were shown to stimulate thyroid cellular proliferation and interfere with TSH binding.21 More recent reviews
have indicated that an autoimmune basis for hyperthyroidism is unlikely and that the disease is more similar to
toxic nodular goiter than to Grave’s disease.22
MOLECULAR ASPECTS OF HYPERTHYROIDISM
More recently, investigators have honed in on the molecular
aspects of feline hyperthyroidism. In cats, the disease is more
similar to toxic nodular goiter in humans and is characterized by autonomous growth of thyroid follicles. The pathogenesis of toxic nodular goiter is an abnormality in the signal
transduction of the thyroid cell. The TSH receptor on the
thyroid cells activate receptor-coupled guanosine triphosphate-binding proteins (G proteins). Uniquely, thyroid cell
proliferation and hormone production are both controlled
by the TSH receptor–G protein–cAMP signaling. Overexpression of stimulatory G proteins and underexpression of inhibitory G proteins have been demonstrated in some humans
with toxic nodular goiter.23,24 Mutations of the TSH receptor
that result in the receptor remaining activated without ligand
(i.e., TSH) have also been reported in humans with toxic
nodular goiter.24–27
The same abnormalities have been investigated in hyperthyroid cats, and it appears that activation mutation of the
TSH receptor may be part of the pathogenesis of hyperthyroidism in some cats.28 Furthermore, abnormalities of G proteins (in particular, significantly decreased G inhibitory
protein expression) have been described in tissues from hyperthyroid cats.29
ticides and herbicides has been associated with thyroid abnormalities in other species.30 In particular, the use of fleacontrol products was associated with an increased risk of
developing hyperthyroidism, but no specific product or ingredient could be identified.31,32
A recent report implicated brominated flame retardants
(BFRs) as carcinogens/goitrogens possibly associated with feline hyperthyroidism.33 Coincidently, BFRs were introduced 30
years ago, around the same time that feline hyperthyroidism
emerged. Bromide, a halide, is an intriguing agent to implicate
in feline hyperthyroidism because of the unique composition
of thyroid hormones that contain the halide iodide. In this abstract, serum levels of lipid-adjusted serum polybrominated
diphenyl ethers (PBDE) were 10 to 400 times higher than those
found in human exposure. The authors theorized that these
findings of high PBDE serum levels are in accord with the most
consistently identified risk factor: indoor living. The authors
also propose that cats are at increased risk because of meticulous grooming behavior and increased exposure to furniture
and carpet. The small size of cats is also a possible risk factor
for increased serum levels of PBDEs.
CAUSES OF FELINE HYPERTHYROIDISM
It is unlikely that autoantibodies to TSH, iodine deficiency, or
iodine excess causes hyperthyroidism. There are unproven
theories that goitrogens, such as BADGE or isoflavones,
PBDEs, and genetic or molecular changes in predisposed individual cats might contribute to hyperthyroidism. Feline hyperthyroidism, like most diseases, is probably caused by a
multitude of interactive factors, including genetics, nutrition,
and environment.
REFERENCES
1. Peterson ME, Johnson JG, Andrews LK. Spontaneous hyperthyroidism
in the cat. Sci Proc Am Coll Vet Intern Med 1979:108.
2. Holzworth J, Theran P, Carpenter JL, et al. Hyperthyroidism in the cat:
ten cases. JAVMA 1980;176:345-353.
3. Peterson ME, Randolph JF, Mooney CT. Endocrine diseases. In: Sherding RG, ed. The Cat: Diseases and Clinical Management, 2nd ed. New
York: Churchill Livingstone; 1994:1403-1506.
ENVIRONMENTAL ASPECTS OF
HYPERTHYROIDISM
4. Edinboro CH, Scott-Moncrieff JC, Janovitz E, et al. Epidemiologic study
of relationship between consumption of commercial canned food and
risk of hyperthyroidism in cats. JAVMA 2004;224:879-886.
In one study, the use of cat litter was associated with an increased risk of hyperthyroidism5; however, there was no significant difference among different brands of litter, suggesting
that the use of litter is simply a marker of cats that are kept indoors.22 Indoor cats are likely to live longer and hence have
a higher risk of developing hyperthyroidism. Exposure to pes-
5. Kass PH, Peterson ME, Levy J, et al. Evaluation of environmental, nutritional and host factors for feline hyperthyroidism. J Vet Intern Med
1999;13:323-329.
6. Johnson LA, Ford HC, Tartellin MF. Iodine content of commerciallyprepared cat foods. N Z Vet J 1992;40:18-20.
7. Tartellin MF, Johnson LA, Cooke RR. Serum free thyroxine levels respond inversely to levels of dietary iodine in the domestic cat. N Z Vet
J 1992;40:66-68.
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8. Kyle AH, Tartellin MF, Cooke RR, et al. Serum free thyroxine levels in
cats maintained on diets relatively high and low in iodine. N Z Vet J
1994;42:101-103.
9. Mooney CT. Pathogenesis of hyperthyroidism. J Vet Med Surg
2002;4:167-169.
10. Ralph AG, Rupp NC, Ward CR. The flavonoid quercetin stimulated mitogenesis in feline hyperthyroid cells [abstract]. J Vet Intern Med
2007;21:595.
11. Court MH, Freeman LM. Identification and concentration of soy
isoflavones in commercial cat foods. Am J Vet Res 2002;63:181-185.
12. Doerge DR, Sheehan DM. Goitrogenic and estrogenic activity of soy
isoflavones. Environ Health Perspect 2002;110(suppl):349-353.
13. White HL, Freeman LM, Mahoney O, et al. Effect of dietary soy on
serum thyroid hormone concentrations in healthy adult cats. Am J Vet
Res 2004;65(5):586-591.
14. Martin KM, Rossing MA, Ryland LM. Evaluation of dietary and environmental risk factors for feline hyperthyroidism. JAVMA 2000;217:853856.
15. Son HY, Nishikawa A, Ikeda T, et al. Lack of effect of soy isoflavone on
thyroid hyperplasia in rats receiving an iodine-deficient diet. Jpn J Cancer Res 2001;92(2):103-108.
16. Dillingham BL, McVeigh BL, Lampe JW, Duncan AM. Soy protein isolates of varied isoflavone content do not influence serum thyroid hormones in healthy young men. Thyroid 2007;17(2):131-137.
17. Teas J, Braverman LE, Kurzer MS, et al. Seaweed and soy: companion
foods in Asian cuisine and their effects on thyroid function in American
women. J Med Food 2007;10(1):90-100.
18. Poole A, van Herwijnen P, Weideli H, et al. Review of the toxicology,
human exposure and safety assessment for bisphenol A diglycidylether
(BADGE). Food Addit Contam 2004; 21(9): 905-919.
19. Kennedy RL, Thoday KL. Autoantibodies in feline hyperthyroidism. Res
Vet Sci 1988;45:300-306.
20. Peterson ME, Livingston P, Brown RS. Lack of circulating thyroid stimulating immunoglobulins in cats with hyperthyroidism. Vet Immunol
Immunopathol 1987;16:277-282.
21. Brown RS, Keating P, Livingston PG, Bullock L. Thyroid growth immunoglobulins in feline hyperthyroidism. Thyroid 1992;2:125-130.
50
Proceedings, 2007 Nestlé Purina Nutrition Forum
22. Peterson ME, Ward C. Etiopathologic findings of hyperthyroidism in
cats. Vet Clin North Am Small Anim Pract 2007;37(4)633-645.
23. Delemer B, Dib K, Patey M, et al. Modification of the amounts of G proteins and of the activity of adenyl cyclase in human benign thyroid tumours. J Endocrinol 1992;132:477-485.
24. Derwahl M, Hamacher C, Papageorgiou G. Alterations of the stimulatory G protein (Gs)-adenylate cyclase cascade in thyroid carcinomas:
evidence for up regulation of inhibitory G protein. Thyroid 1995;5(suppl
1):S-3.
25. Russo D, Arturi F, Suarez HG, et al. Thyrotropin receptor gene alterations in thyroid hyperfunctioning adenomas. J Clin Endocrinol Metab
1996;81:1548-1551.
26. Fuhrer D, Holzapfel HP, Wonerow P, et al. Somatic mutations in the
thyrotropin receptor gene and not in the Gs alpha protein gene in 31
toxic thyroid nodules. J Clin Endocrinol Metab 1997;82:3885-3891.
27. Parma J, Duprez L, Van Sande J, et al. Diversity and prevalence of somatic mutations in the thyrotropin receptor and Gs alpha genes as a
cause of toxic thyroid adenomas. J Clin Endocrinol Metab 1997;82:26952701.
28. Peeters ME, Timmermans-Sprang EP, Mol JA. Feline thyroid adenomas
are in part associated with mutations in the G (s alpha) gene and not
with polymorphisms found in the thyrotropin receptor. Thyroid
2002;12:571-575.
29. Hammer KB, Holt DE, Ward CR. Altered expression of G proteins in
thyroid gland adenomas obtained from hyperthyroid cats. Am J Vet Res
2000;61:874-879.
30. Gaitan E. Goitrogens in food and water. Annu Rev Nutr 1990;10:21-39.
31. Scarlett JM, Moise NS, Ravl J. Feline hyperthyroidism: goitrogens descriptive and case controlled study. Prev Vet Med 1988;6:295-309.
32. Olczak J, Jones BR, Pfeiffer DU, et al. Multivariate analysis of risk factors
for feline hyperthyroidism in New Zealand. N Z Vet J 2005;53:53-58.
33. Dye JA, Venier M, Ward CA. Brominated-flame retardants (BFRs) in cats:
possible linkage to feline hyperthyroidism [abstract]. J Vet Intern Med
2007;21:595.
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SCIENTIFIC PROGRAM: FOCUS ON FELINES
Measures of Disease Activity in Feline
Inflammatory Bowel Disease
Albert E. Jergens, DVM, PhD, DACVIM
Department of Veterinary Clinical Sciences, College of Veterinary Medicine,
Iowa State University, Ames, Iowa
Research over the past several years has substantially expanded our understanding of feline inflammatory bowel
disease (FIBD) and its underlying pathomechanisms (Figure 1). Advances in basic immunologic techniques and molecular biology have provided evidence that FIBD likely
results from a dysregulated immunologic response to environmental triggers, including luminal bacteria and specific
antigens.1 In addition to these basic research findings,
emerging clinical data offer insight into the histopathology,
clinical immunology, and assessment of disease severity in
affected cats at diagnosis and in response to therapeutic
intervention. Additionally, preliminary data suggest that
some staging criteria have direct application to cats with
other forms of chronic enteropathy, such as food-responsive enteropathy.
The World Small Animal Veterinary Association Congress
GI Standardization Group is working diligently to produce
and validate a workable, standardized histopathologic scoring system for GI inflammation that clinicians and pathologists can apply universally.7 This grading protocol covers the
gastric fundus and pylorus, duodenal mucosa, and colonic
mucosa. For each anatomic region, a narrative and visual
(photomicrographic) template that defines the normal histologic appearance of the tissue and key morphologic and inflammatory changes (by severity) has been developed.
Analysis of approximately 250 endoscopic biopsies collected
by gastroenterologists worldwide using standardized reporting forms is presently under way.
HISTOPATHOLOGIC GUIDELINES FOR
DIAGNOSING FIBD
In contrast to canine IBD, in which a balanced ratio of T-helper
1 (Th1) to T-helper 2 (Th2) mucosal cytokine pattern emerges,
data to date suggest that FIBD cytokine expression is more
overtly Th1-like and broadly correlates to histopathologic inflammation. In one small study of 12 cats with IBD,8 endoscopic biopsies were evaluated for the presence of cellular
infiltrates and morphologic changes and then correlated to levels of cytokine mRNA quantitated by real-time polymerase
chain reaction. In general, morphologic changes (e.g., epithelial
alterations, villus fusion, atrophy) were associated with upregulated expression of interleukin-1β (IL-1β), IL-8, IL-12, and interferon-γ (IFN-γ) as well as IL-10 in diseased cats. Furthermore,
IBD grade correlated with IL-10 and IL-12, with IL-10 highest in
cats with severe FIBD. Interestingly, cytokine upregulation was
not correlated with the density of the mucosal cellular infiltrate.
A separate investigation evaluated cytokine mRNA expression in cats with chronic enteropathy caused by FIBD and nonIBD GI diseases.9 The results of this study were analyzed on the
basis of either clinical presentation or histopathologic evidence
of intestinal inflammation. Clinically normal cats and cats
Histology is key to confirming diagnosis and eliminating
some other diseases, but standardized grading criteria have
not been adopted. Several qualitative and semiquantitative
histopathologic scoring systems for IBD have been proposed
(Box 1).2–5 In most instances, these scoring systems are larger,
case-based studies that use a spectrum of histologic criteria
of mucosal inflammation with commentary on lamina propria cellularity. Endoscopically obtained gastrointestinal (GI)
tract mucosal biopsy collection remains the gold standard
but presents a variety of challenges for clinicians and pathologists. It is recognized that these specimens are small, prone
to procurement and processing artifacts, and difficult to optimally orient for accurate morphologic characterization. Additionally, extensive interobserver variability in interpretation
between pathologists can occur.6 Histopathologic diagnostic
criteria of IBD should clearly define morphologic evidence
of mucosal inflammation; however, which criteria are most
relevant is presently a matter of debate.
MUCOSAL CYTOKINE EXPRESSION AND
CORRELATION TO HISTOLOGY IN FIBD
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Other environmental factors
Page 52
Microbes
Box 1. Histopathologic Hallmarks of
Feline Inflammatory Bowel Disease
• Changes in surface or cryptal epithelia (erosions, necrosis,
hyperplasia, increased intraepithelial lymphocytes)
• Marked alterations in lamina propria cellularity
Barrier
Function
Host Factors
IBD
Innate and
Adaptive
Immunity
Noted Disturbances:
GIT Signs
Histologic lesions
MHC II Expression
Pro-inflammatory Cytokines
Bacterial Antibody Responses
Mucosally-Adherent Bacteria
Figure 1. Proposed IBD etiopathogenesis. Intestinal inflammation
of feline IBD likely results from complex interactions between the
resident microflora and the mucosa. Intestinal inflammation results
from host (genetic) and environmental factors that affect barrier
function and innate and adaptive immunity. (Adapted from Xavier
RJ, Podolsky DK. Unravelling the pathogenesis of inflammatory
bowel disease. Nature 2007;448:427-430.)
with FIBD showed increased expression of immunoregulatory
(IL-10, tumor growth factor-β [TGF-β]) and proinflammatory
(IL-6, IL-18, tumor necrosis factor-α [TNF-α], and IL-12p40)
cytokines relative to cats with other GI diseases. Histopathologic analysis showed that cats with intestinal inflammation
had upregulated expression of IL-6, IL-10, IL-12p40, TNF-α,
and TGF-β, compared with those with normal intestinal morphology. These accumulated observations indicate that FIBD
is characterized by immune dysregulation that parallels morphologic evidence of intestinal inflammation.
CLINICAL MEASURES OF DISEASE
ACTIVITY IN FIBD
Well-defined clinical criteria for assessment of FIBD activity
have not been published, presumably reflecting the generally
sparse number of studies reported and the inability of the researchers to critically assess disease activity other than by the
severity of histologic lesions. Clearly, several themes emerge
from these earlier evidence-based investigations: (1) GI signs of
anorexia, weight loss, and vomiting predominate with gastric
or small-intestinal IBD; (2) GI signs of hematochezia, mucoid
feces, tenesmus, or increased frequency of defecation are commonly observed with colonic IBD; (3) biochemical changes of
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Proceedings, 2007 Nestlé Purina Nutrition Forum
• Mucosal architectural changes (villus blunting or fusion, mucosal
edema, fibrosis, lymphatic dilation)
• Submucosal cellular infiltration
altered plasma protein concentrations (e.g., hyperglobulinemia, hypoalbuminemia) and increased serum concentration
of hepatic enzymes (e.g., alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [ALP])
are often observed; and (4) histologic lesions of lymphocytic–
plasmacytic mucosal cellular infiltrates predominate (Box 2).
A possible first step in the development of an FIBD activity
index (FIBDAI) would be collecting a wide range of variables,
including prominent GI signs (generally reported by the client
or clinician) and select laboratory parameters, and correlating
their association to the severity of histologic lesions. One pilot
study has taken this exact approach.10 An FIBDAI was prospectively evaluated in 27 cats with FIBD before and during therapeutic intervention. Variables included histology, GI signs,
serum total protein and phosphorous concentrations, serum
ALT and ALP, and endoscopic lesions. Complete response to
prednisolone therapy was observed in 22 of 27 FIBD cats, and
remission was achieved in the remaining 5 cats with the addition of chlorambucil. Alterations in clinical scoring indexes
were observed in all FIBD cats as a consequence of medical
therapy. Pretreatment FIBDAI scores (mean score: 7.8) were
markedly reduced during the 14- to 21-day treatment period
(mean posttreatment FIBDAI score: 0.8). These preliminary
data suggest that clinical scoring of FIBD is suitable for clinical
evaluation of the therapeutic effect in these patients.
LABORATORY (SURROGATE) MARKERS
OF DISEASE ACTIVITY IN FIBD
Acute-phase proteins (APPs), such as haptoglobin (HAP),
serum amyloid A (SAA), and acid glycoprotein (AGP), are
plasma proteins that increase in concentration after infection,
inflammation, or trauma. Serum APPs are routinely measured
in human clinical laboratories to assist in assessing the activity of disease and its response to treatment. Previous studies11,12 have shown that concentrations of some APPs correlate
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MEASURES OF DISEASE ACTIVITY IN FELINE INFLAMMATORY BOWEL DISEASE
Box 2. Clinical and Laboratory Parameters
Perturbed in Feline Inflammatory Bowel Disease
• Clinical scores
• Increased hepatic enzymes
• Altered plasma proteins
• Histologic grading
• Endoscopic lesions
• Hypocobalaminemia
well with human and canine IBD, but few detailed reports are
available for cats. In a prospective study that included 27 cats
with FIBD,11 we investigated whether serum APPs would be
altered at diagnosis and in response to therapeutic intervention compared with healthy cats. All of the cats in this study
had an extensive diagnostic workup, including a dietary trial
with an elimination diet to exclude adverse food reactions and
GI tract endoscopic biopsy. Additionally, all cats were clinically scored with the FIBDAI for disease severity at diagnosis
and after 14 to 21 days of medical therapy.
Although it was hypothesized that cats with FIBD would
have increased APPs, the highest serum concentrations were
observed in cats with non-IBD chronic enteropathy. Baseline
APPs (HAP, AGP) during the initial examination were marginally increased in cats with IBD compared with healthy
cats. SAA was not detectable in any of the feline groups. Although medical therapy resulted in a significant reduction of
clinical disease severity in FIBD, this was not accompanied
by reduced serum concentrations of APPs. Serum HAP
showed a negative correlation to therapy, and posttreatment
values were increased compared with pretreatment levels,
suggesting that glucocorticoids likely induce serum concentrations of APPs. It was concluded that APPs are not suitable
markers for assessment of disease activity in FIBD.
CONCLUSIONS
Measures of disease activity for FIBD and other forms of feline
chronic enteropathy are presently being designed. Cats with
FIBD clearly have defined markers of intestinal inflammation,
such as altered proinflammatory cytokine expression profiles
and morphologic features of mucosal inflammation on review
of histologic specimens. Preliminary results from pilot studies
suggest that clinical variables may be useful to assess the initial
disease severity and response to treatment in cats with FIBD. Future studies evaluating the role of fecal and serologic markers of
inflammation in cats with chronic enteropathy are warranted.
REFERENCES
1. Jergens AE. Inflammatory bowel disease: current perspectives. Vet Clin
North Am Small Anim Pract 1999;29:501-521.
2. Jergens AE, Moore FM, Haynes JS, et al. Idiopathic inflammatory bowel disease in dogs and cats: 84 cases (1987–1990). JAVMA 1992;201:1603-1608.
3. Dennis JS, Kruger JM, Mullaney TP. Lymphocytic/plasmacytic gastroenteritis in cats: 14 cases (1985–1990). JAVMA 1992;200:1712-1718.
4. Wilcock B. Endoscopic biopsy interpretation in canine or feline enterocolitis. Semin Vet Med Surg 1992;7:162-171.
5. Roth L, Walton AM, Leib MS, et al. A grading system for lymphocyticplasmacytic colitis in dogs. J Vet Diagn Invest 1990;2:257-262.
6. Willard MD, Jergens AE, Duncan RB, et al. Interobserver variation
among histopathologic evaluations of intestinal tissues from dogs and
cats. JAVMA 2002;220:1177-1182.
7. Day MJ. Report from the WSAVA GI Histopathologic Standardization
Group. Proc ACVIM, 2007.
8. Goldstein RE, Greiter-Wilke A, McDonough SP, et al. Quantitative evaluation of inflammatory and immune responses in cats with inflammatory bowel disease [abstract]. J Vet Intern Med 2003;17:411-412.
9. Nguyen VN, Taglinger K, Helps CR, et al. Measurement of mucosal cytokine mRNA expression in intestinal biopsies of cats with inflammatory enteropathy using quantitative real-time RT-PCR. Vet Immunol
Immunopathol 2006;113:404-414.
10. Crandell JM, Jergens AE, Morrison JA, et al. Development of a clinical
scoring index for disease activity in feline inflammatory bowel disease
[abstract]. J Vet Intern Med 2006;20:788.
11. Jergens AE, Crandell JM, Morrison JA, et al. Serum acute phase proteins in
feline inflammatory bowel disease [abstract]. J Vet Intern Med 2007;21:612.
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Nutrition Forum
Research Abstracts:
Oral Presentations
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RESEARCH ABSTRACTS: ORAL PRESENTATION
Dietary Variables That Predict Glycemic Responses
to Whole Foods in Cats
a
N.J. Cave,a J.A. Monro,b and J.P. Bridgesa
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
b
New Zealand Institute for Crop and Food Research Limited, Palmerston North, New Zealand
The glycemic load of high-carbohydrate diets has
been proposed to be suboptimal for cats. We hypothesized that the in vitro carbohydrate digestibility
of diets would predict the in vivo glycemic response
or that other dietary variables would explain any difference.
The in vitro digestibility of 18 whole dry diets was
determined by simulated physiologic digestion. Diets
were ranked according to the rate of glucose release
over time (GGE) relative to total available carbohydrates. Six diets spanning the range of GGE were selected for in vivo assessment. Six cats were each pre-fed
one of the diets for 7 days followed by a 16-hour fast;
they were then fed enough diet to provide 1 g/kg of
available carbohydrates. Serial blood glucose was assayed until it had returned to baseline.
Despite a wide range of in vitro digestibilities and
compositions, there was little difference in incremental area under the curve (AUCinc) between diets,
with glucose absorption occurring over 10 to 12
hours for all diets. There was no significant association between AUCinc and in vitro digestibility, but
GGE60 was associated with the baseline fasted blood
glucose (r2 = .35; P = .035). The fasted blood glucose predicted the absolute AUC (AUCabs; r2 = .66;
P < .001), the AUCinc (r2 = –.73; P < .001), and peak
glucose responses (r2 = .59; P < .001). AUCinc was not
associated with dietary crude fiber, fat, protein, carbohydrate, or physical biscuit characteristics. Glycemic
responses (AUCinc) to whole foods are prolonged and
are not predicted by the digestibility of the carbohydrate component.
When the equivalent amount of available carbohydrate is fed, incremental glycemic responses to different diets are unaffected by dietary fiber, fat, protein,
carbohydrate type, or physical biscuit characteristics.
Whereas fasted blood glucose after a few days of feeding appears to be a good indicator of the long-term
glycemic load of a diet (AUCabs), AUCinc is probably
determined simply by the rate of gastric emptying.
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Spaying Affects Blood Metabolites and
Adipose Tissue Gene Expression in Cats
K.R. Belsito,a B.M. Vester,a T. Keel,b T.K. Graves,b,c and K.S. Swansona,b,c
a
Department of Animal Sciences, University of Illinois, Urbana, Illinois
b
Department of Veterinary Clinical Medicine, University of Illinois, Urbana, Illinois
c
Division of Nutritional Sciences, University of Illinois, Urbana, Illinois
Although spaying is known to contribute to obesity,
the role of adipose tissue is poorly understood. Thus,
our objectives were to examine the effects of spaying
on serum metabolite concentrations and adipose tissue and skeletal muscle gene expression in cats.
Eight adult (>1 year old) domestic shorthair cats
were fed a commercial dry diet throughout the study.
After a 2-week baseline period (week 0), cats were
spayed and fed to maintain an ideal body weight for
12 weeks. After 12 weeks, cats were fed ad libitum for
an additional 12 weeks. Blood samples were collected
at weeks 0, 6, 12, 18, and 24, and adipose tissue and
skeletal muscle biopsies were collected at weeks 0, 12,
and 24. Data were analyzed using the mixed-model
method of SAS (Cary, NC).
Fasting serum glucose and triglycerides were increased (P < .05) at week 24, and plasma leptin tended
to be increased (P < .10) at weeks 18 and 24. Adipose
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Proceedings, 2007 Nestlé Purina Nutrition Forum
lipoprotein lipase (LPL) mRNA was decreased (P < .05)
at weeks 12 and 24. Adipose hormone-sensitive lipase
(HSL) mRNA was decreased (P < .05) at week 24. Adipose tumor necrosis factor-α mRNA tended to be decreased (P < .10) at week 12, and interleukin-6 (IL-6)
mRNA was increased (P < .05) at weeks 12 and 24.
Adipose leptin mRNA was decreased (P < .05) at week
12, and adiponectin mRNA tended to be decreased
(P < .10) at week 24. Changes in HSL and LPL mRNA
suggest changes in adipose tissue lipid metabolism as
a result of spaying and weight gain, likely contributing
to increased circulating triglycerides. Decreased
adiponectin and increased IL-6 mRNA may be early
signals of adipose tissue dysregulation and contribute
to insulin resistance.
Our results demonstrate that adipose tissue is sensitive to spaying or weight gain (or both), justifying
further research in this area.
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RESEARCH ABSTRACTS: ORAL PRESENTATION
Effects of Spaying on Food Intake, Weight Gain,
Body Condition Score, Activity, and Body Composition in
Cats Fed a High-Protein versus Moderate-Protein Diet
B.M. Vester,a K.J. Liu,b T. Keel,c T.K. Graves,c,d and K.S. Swansona,c,d
Department of Animal Sciences, University of Illinois, Urbana, Illinois
b
Natura Manufacturing, Inc., Fremont, Nebraska
c
Division of Nutritional Sciences, University of Illinois, Urbana, Illinois
d
Department of Clinical Veterinary Medicine, University of Illinois, Urbana, Illinois
a
High-protein diets have been used to promote weight
loss in cats, but the effect of feeding high-protein
diets after spaying to maintain weight has not been
determined. The objective of this study was to evaluate cats fed either a high-protein diet (52.9% crude
protein [CP] on a dry matter basis [DMB]) or a moderate-protein diet (34.3% CP DMB; 3.9 and 4.2 kcal/g
calculated metabolizable energy, respectively) following ovariohysterectomy.
Food intake, body weight (BW) gain, body condition score (BCS), body composition, and activity level
were measured in eight cats (four cats/treatment). Cats
older than 1 year underwent ovariohysterectomy on
week 0 and were fed ad libitum for 24 weeks. Food
intake was measured daily, and BW and BCS were
measured weekly. Activity was measured for 6 consecutive days before weeks 0, 12, and 24, and body
composition was determined by dual-energy x-ray absorptiometry at weeks 0, 12, and 24.
Food intake and BW were markedly changed (P < .05)
over time in all cats and tended to be increased (P < .10)
in cats fed a high-protein diet. BCS was greater (P < .05)
in cats fed the high-protein diet but increased (P < .05)
over time regardless of dietary treatment. Total activity, measured using Actical activity collars (Mini-Mitter, Bend, OR), decreased (P < .05) from week 0 to
weeks 12 and 24. Body composition did not change due
to diet; however, body fat percentage increased (P < .05)
over time. Grams of lean tissue showed a curvilinear
(P < .05) effect over the course of the study, but percentage of lean tissue tended to decrease (P < .10) over
time. Bone mineral content was increased (P < .05) at
week 12 in cats fed the high-protein diet. This is likely
to support the increased BW because of the large increase in food intake early after spaying in the cats fed
the high-protein diet, which may have been due to the
high palatability of this diet.
Based on these data, feeding a diet ad libitum after
spaying, regardless of protein level in the diet, may
increase the incidence of obesity in cats.
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Higher Protein Consumption during Weight Loss Allows Higher
Caloric Intake for Maintenance of Body Weight in Cats
R.S. Vaconcellos,a N.C. Borges,a K.N.V. Gonçalves,a F.J.A. de Paula,b E.B. Malheiros,a
R.S. Bazolli,a and A.C. Carciofia
a
School of Agrarian and Veterinarian Sciences, State University of São Paulo, São Paulo, Brazil
b
Hospital of Clinics, Medical School of Ribeirão Preto, State University of São Paulo, São Paulo, Brazil
The objective of this study was to compare energy requirements for weight stabilization of cats that lost
weight while consuming two different dietary protein
levels. Fifteen adult neutered cats were divided into
two groups: a control group and a high-protein group.
Two procedures were followed: In the first part of
the study, two diets were used to achieve a controlled
20% weight loss (the control group was given a 29%
crude protein [CP] diet, and the high-protein group
was given a 43% CP diet). Groups had similar body
composition (dual-energy x-ray absorptiometry) before weight loss; after weight loss, the control group
had higher fat body mass (FM; 28.8% ± 1.6%) and
lower lean body mass (LM; 68.4% ± 1.6%) than the
high-protein group (FM: 23.4% ± 3.2%; LM: 73.5%
± 3.1%; P < .01).
Cats were then fed a 39% CP diet to maintain body
weight for 17 weeks. Energy ingestion was divided into
three periods: initial (weeks 0 to 6), middle (weeks 7
to 12), and final (weeks 13 to 17). At the end of the 17
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Proceedings, 2007 Nestlé Purina Nutrition Forum
weeks, there was no difference in body composition
between groups (control group: FM = 24.9% ± 2.2%;
LM = 72.8% ± 2.8%; high-protein group: FM = 24.1%
± 1.9%; LM = 72.2% ± 1.1%). From weeks 7 to 12, energy requirements gradually increased and did not stabilize in either group. Energy requirements were
similar during the first 6 weeks of the study (control
group: 93.6 ± 2.8 kcal/kg BW0.4; high-protein group =
97.2 ± 1.9 kcal/kg BW0.4) but significantly higher in the
high-protein group during weeks 7 to 12 (control
group = 96.7 ± 2.2 kcal/kg BW0.4; high-protein group =
111.9 ± 1.8 kcal/kg BW0.4; P < .001) and weeks 13 to 17
(control group = 110.6 ± 2.2 kcal/kg BW0.4; high-protein group = 127.7 ± 2.0 kcal/kg BW0.4; P < .01).
Based on our results, we conclude that high protein ingestion during weight loss periods provides
higher energy requirements to stabilize body weight
during maintenance. Nutritional composition of the
maintenance diet may contribute to the recovery of
lean body mass lost during caloric restriction.
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RESEARCH ABSTRACTS: ORAL PRESENTATION
Effect of a Low-Protein Diet on Gut Morphology in Cats
D.G. Thomas,a C.E. Ugarte,a K.J. Rutherfurd-Markwick,a and W.H. Hendriksb
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
b
Animal Nutrition Group, Department of Animal Sciences, Wageningen University, Wageningen, The Netherlands
a
Ingesting proteins and amino acids can impact the
health of cats in two ways: (1) in a nutritive sense by
supplying necessary energy and amino acid requirements, and (2) by acting as bioactive molecules and
influencing functions within the body, including intestinal health. Because there is little information
available on the influence of diet on gut health in
cats, this preliminary study was designed to generate
information on changes in gut morphology in response to a low-protein diet.
Eleven adult feral cats (six males, five females)
were trapped as part of normal pest-control measures
in the Manawatu region of New Zealand. Before
being included in the study, the cats were sedated and
screened by a veterinarian for feline immunodeficiency virus or feline leukemia virus. Cats were
housed in single-metabolism cages and fed either a
control (32.7% protein, 21.0% fat, 42.5% carbohydrate) diet (n = 5) or a low-protein (20.9% protein,
25.5% fat, 49.9% carbohydrate), semi-synthetic diet
(n = 6) for 10 weeks before being euthanized. Samples of intestine (~ 5 cm in length) were excised from
areas 15% (duodenum), 30% (jejunum), and 60%
(ileum) along the length of the tract and processed
for histologic analysis. Transverse sections (5 μm) of
tissue were cut, and each specimen was stained with
alcian blue, hematoxylin–eosin and examined by
light microscopy (original magnification, ×100). SigmaScan (Systat Software, Chicago, IL) was used to
measure villous height, crypt depth, and epithelial
cell thickness of 10 villi in each tissue sample.
Similar morphologic characteristics were observed
in the duodenal, jejunal, and ileal segments. Animals
fed the low-protein diet had consistently longer villi,
deeper crypts, and a thicker epithelial cell layer than
animals fed the control diet. This indicates that the animals responded to the low-protein diet by increasing
the gut surface area to maximize nutrient absorption.
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Variations in Dietary Fat Affect Lipid Metabolism
in Domestic Cats
a
M.K. McClure,a R.J. Angell,a K.E. Bigley,a K. Fennell,a and J.E. Bauer b
Companion Animal Nutrition Laboratory, Texas A&M University, College Station, Texas
b
Intercollegiate Faculty of Nutrition, Texas A&M University, College Station, Texas
Feline fatty acid metabolism may be directly affected
by alterations of dietary fat intake. This study investigated the effect of different types of dietary fat on
plasma triacylglycerol, total cholesterol, lipoproteincholesterol, and nonesterified fatty acid (NEFA) concentrations.
Thirty clinically normal, sexually intact young
adult female cats were randomized into three groups
of 10. Each group was fed a complete, balanced, commercial, dry, extruded-type basal diet supplemented
with equal amounts of fat, differing only in fatty acid
composition. The diets were designated as high-oleic
sunflower (HOS), menhaden fish oil (MFO), and safflower oil (SFO). The HOS diet contained high
amounts of oleic acid, the MFO diet contained high
amounts of long-chain omega-3 fatty acids, and the
SFO diet contained linoleic acid. Diets were fed for
28 days, with blood collected on days 0, 14, and 28.
Using repeated measures analysis of variance and
post hoc comparisons, the MFO diet showed a statis-
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Proceedings, 2007 Nestlé Purina Nutrition Forum
tically significant (P < .05) triacylglycerol-lowering effect despite the already low-normal triacylglycerol
levels typically observed. Lipoprotein electrophoresis
revealed a statistically significant lowering of the prebeta band (i.e., very-low-density lipoprotein) triacylglycerol in the MFO diet (P < .05) consistent with
plasma triacylglycerol lowering. Whether triacylglycerol lowering in normal cats is beneficial is unknown.
No main time or diet effects were found on total cholesterol concentrations, and no changes were observed in mean plasma NEFA concentrations. In some
cats, an additional lipid-staining region was found on
the electrophoretogram, which migrated similar to
plasma albumin; however, this region did not correlate with plasma NEFA concentrations.
Additional studies to investigate these effects are
in progress, including studies of plasma phospholipid and red blood cell fatty acids, cholesteryl ester
and lecithin acyl transferase activities, and indices of
fatty acyl desaturase enzyme activities.
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RESEARCH ABSTRACTS: ORAL PRESENTATION
Impact of Dietary Trans-Fatty Acid on Serum Insulin
and Glucose Concentrations in Cats
a
P.A. Schencka and S.K. Aboodb
Department of Pathobiology and Diagnostic Investigation, Diagnostic Center for Population and Animal Health,
Michigan State University, East Lansing, Michigan
b
Department of Small Animal Clinical Sciences, Michigan State University, East Lansing, Michigan
Diabetes mellitus (DM) in cats is characterized by insulin resistance. Overweight and older cats are at increased risk of developing DM. In humans, dietary
trans-fatty acids (TFA) increase insulin resistance, especially when fed at a level greater than 1% energy
(%E). Exposure to dietary TFA may increase insulin
resistance and type II DM in cats. The objective of this
study was to determine if dietary intake of TFA was
higher in cats at increased risk for DM.
Cats were grouped as follows: group 1 (normal; n =
27)—less than 10 years of age, body condition score
(BCS) of 4 to 6; group 2 (fat; n = 23)—less than 10 years
of age, BCS of 7 to 9; and group 3 (senior; n = 6)—10
years of age or older, BCS of 4 to 6. Serum was collected for general analysis, and each cat’s diet was analyzed for TFA.
Group 2 cats had a significantly higher BCS (mean:
7.6), body weight (mean: 14.1 lb), and percentage of
body fat (mean: 5.0%) than group 1 cats (mean: 5.3
BCS, 10.1 lb body weight, 3.9% body fat) or group 3
cats (mean: 5.0 BCS, 9.0 lb body weight, 3.6% body
fat). Group 2 cats showed a significantly higher (P < .05)
concentration of serum insulin (mean: 54.5 pmol/L)
and had a higher serum insulin:glucose ratio (mean:
9.8) than group 1 cats (mean: 39.1 pmol/L serum insulin, 6.8 insulin:glucose ratio) or group 3 cats (mean:
28.0 pmol/L serum insulin, 5.9 insulin:glucose ratio)
cats. There were no significant differences in serum glucose, serum or dietary TFA concentrations, or dietary
%E derived from TFA. Insulin concentration and insulin:glucose ratio were significantly correlated to BCS,
body weight, and percentage of body fat but not to
serum TFA, dietary TFA, or dietary %E from TFA.
Cats at higher risk for DM did not show elevated
serum TFA or dietary intake of TFA. Although there
does not appear to be a direct correlation of dietary
TFA to insulin concentration, TFA could still contribute
to the development of DM in predisposed individuals.
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Sequencing and Characterization of Feline Pancreatic
Glucokinase cDNA
S. Lindbloom, M. LeCluyse, E. Hiskett, and T. Schermerhorn
Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas
Glucokinase (GK) is an important metabolic enzyme
that is the “glucose sensor” in pancreatic beta cells.
GK activity in beta cells correlates with blood glucose
concentration and links glucose metabolism to activation of cellular pathways that promote insulin secretion. The importance of pancreatic GK expression
for normal glucose tolerance and insulin secretion is
well established, and GK mutations cause diabetes in
mammals. GK mRNA is known to be expressed in the
feline pancreas, but the molecular details of feline
pancreatic GK have not been previously investigated.
This study’s objectives were to determine the sequence of feline pancreatic GK cDNA, predict the
amino acid sequence of the feline pancreatic GK protein, and perform a comparative analysis of feline
pancreatic GK sequence and structure.
GK mRNA from the pancreas of a normal cat was
analyzed with reverse transcription polymerase chain
reaction using species-specific primers. The elucidated
cDNA sequence was used to predict protein sequence.
Protein structure was modeled using molecular modeling software. The cDNA coding region contains 1,398
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Proceedings, 2007 Nestlé Purina Nutrition Forum
bp and encodes a 465–amino acid protein (GenBank
EF121813). The predicted feline pancreatic GK protein
is 89% to 94% identical to other mammalian GK proteins and contains 15 unique residues, 5 of which are
nonconserved substitutions. Substrate binding, protein recognition, and other important functional motifs are conserved in feline GK. The feline GK protein
model has two globular domains separated by a hinge
region, similar to known GK structures. Interestingly,
modeling studies indicated the region around nonconserved tryptophan35 in wild-type feline pancreatic
GK has structural similarities to human GK with an
R36W mutation, which causes type-2 maturity-onset
diabetes mellitus of the young.
In conclusion, feline pancreatic GK has all major
sequence and structural motifs found in noncarnivores, but nonconserved amino acids in the feline sequence may indicate species specificity. The aggregate
effect of the nonconserved residues on protein function and the significance of these variations with respect to feline glucose metabolism or development
of diabetes is unknown.
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RESEARCH ABSTRACTS: ORAL PRESENTATION
Effects of Epigallocatechin Gallate Singly and in Combination
with Lactoferrin on Oral Health in Cats
a
S. Krammer-Lukas,a K. Cramer,a U. Wehr,b S. Gorissen,b and K. Elsbett b
Animal Nutrition and Health Research and Development, DSM Nutritional Products, Kaiseraugst, Switzerland
b
Institute of Nutrition, Ludwig-Maximilian-University, Munich, Germany
Periodontopathic conditions are the most common
diseases in dogs and cats. Prophylaxis is usually limited to professional dental cleaning under anesthesia, especially in cats. Special diets that reduce plaque
and calculus accumulation are formulated to extend
the time between dental cleanings. Epigallocatechin
(EGCG) and lactoferrin are already used in humans
to maintain oral health because of these substances’
antibacterial effect. The aim of this study was to investigate the effect of EGCG singly and in combination with lactoferrin in a regular, dry, nondental diet
on the oral health of cats.
In two consecutive trials, a total of 18 domestic
short-haired cats (age: 3.83 ± 1.85 years old; body
weight: 4.2 ± 1.1 kg) were divided on the basis of
plaque score, age, and gender into two equal groups
of nine animals each. For 28 days, animals were fed
either a control or treated diet (trial 1: 227 mg
EGCG/kg cat food; trial 2: EGCG and lactoferrin each
300 mg/kg cat food). General and dental health were
investigated in the study. Because the “clean tooth
model” was used, all cats received a dental cleaning
before the 28-day feeding period.
EGCG alone proved able to inhibit the growth of
bacteria taken from the feline oral cavity in vitro and
seemed to have an effect on the cats’ antioxidant status. Supplementation with EGCG in combination
with lactoferrin led to slightly lower plaque and calculus indexes compared with the control group. The
gingivitis index decreased significantly in the
EGCG/lactoferrin group, and compared with the control group, the probing depth of the supplemented
diet group was significantly lower at the end of the
experimental phase of the EGCG/lactoferrin test.
Altogether, the combination of EGCG and lactoferrin could be valuable when used along with established solutions for reducing plaque and calculus
(e.g., fiber-containing kibbles or edible chews).
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Nutrition Forum
Research Abstracts:
Poster Presentations
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Effect of Isoflavones, Conjugated Linoleic Acid, and L-Carnitine
on Weight Loss and Oxidative Stress in Overweight Dogs
Y. Pan,a I. Tavazzi,b J.-M. Oberson,b L.B. Fay,b and W. Kerr a
a
Nestlé Purina Research, St. Louis, Missouri
b
Nestlé Research Center, Lausanne, Switzerland
This study investigated whether soy isoflavones alone
or a blend of soy isoflavones, conjugated linoleic
acid, and L-carnitine can promote weight loss, preserve lean body mass, and reduce oxidative stress in
overweight dogs. Overweight Labrador retrievers and
Siberian huskies were randomized into three groups
(control, isoflavones, blend diets) and fed 70% of
their maintenance energy requirement (MER) during
the first 3 months of weight loss. Dogs that failed to
reach their ideal body fat levels after the first 3
months of weight loss were fed 55% of their MER
during the second 3 months of weight loss. Dual-energy x-ray absorptiometry scans were obtained 3 and
6 months after the study was initiated.
At the end of the study, the percentage of Labrador
retrievers with their body fat reduced to ideal levels
was 66.7%, 75%, and 85.7% for the control,
isoflavone, and blend diets groups, respectively; the
percentage of Siberian huskies with their body fat reduced to ideal levels was 33.3%, 50%, and 50% for
the control, isoflavone, and blend diets groups, respectively. Compared with the control diet, both the
isoflavone and blend diets groups significantly reduced plasma isoprostanes, and the blend diet completely prevented loss of lean body mass and
significantly increased lean body mass after the first 3
months of weight loss.
In summary, more dogs in the isoflavone and
blend diets groups tended to have their body fat percentages reduced to ideal levels than did control dogs.
The blend diet prevented loss of lean body mass in
overweight dogs during weight loss, and soy
isoflavones in the weight-loss diets reduced in vivo
oxidative damage in overweight dogs.
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Postfeeding Satiety and Weight Loss of Dogs Fed a
Vegetable-Based Fiber Supplement
a
Y. Mitsuhashi,a K. Bigley,a and J.E. Bauer a,b
Companion Animal Nutrition Laboratory, Texas A&M University, College Station, Texas
b
Intercollegiate Faculty of Nutrition, Texas A&M University, College Station, Texas
Dietary insoluble fiber is believed to support weight
loss by increasing satiety and the mass of the food
consumed without adding calories. Therefore, we
measured satiety and weight loss in beagles fed a vegetable-based fiber supplement.
Two diets that differ in fiber content were fed: Purina ONE® Healthy Weight Formula (Purina ONE;
Nestlé Purina PetCare, St. Louis, MO) was compared
with a diet consisting of Purina ONE plus a vegetablebased fiber supplement (FS); crude fiber contents were
2.6% (Purina ONE) versus 5.4% (FS) dry matter.
For the satiety studies, 12 to 14 adult female beagles
with average body fat of 38.4% ± 1.9% and body weight
of 13.8 ± 0.9 kg were randomly divided into two groups.
Diets were fed at 8:00 AM and 3:00 PM (7-hour interval)
during one trial and at 8:00 AM and 11:00 AM (3-hour interval) for 15 minutes each during a second trial. The
amounts offered at each feeding were 1.2 times the maintenance energy requirement (MER) using a crossover design. Blood samples were collected 45 and 120 minutes
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Proceedings, 2007 Nestlé Purina Nutrition Forum
postprandially, and food intakes were recorded.
For the weight loss study, seven obese beagles were
selected (average body fat: 45.1% ± 1.6%; body weight:
15.2 ± 1.0 kg) and divided into two groups. The diets
were fed once daily (approximately 60% of obese
MER) for 42 days. Postprandial blood samples were
collected at 0 and 60 minutes on days 1, 28, and 42.
Food intakes and body weight were recorded daily
and weekly, respectively.
As expected, all dogs lost similar amounts of body
weight and body fat independent of diet. In the satiety trials, intake at both the 3- and 7-hour intervals
was not different from the control group; however, significantly fewer total calories were consumed with the
FS diet during the 3-hour interval. FS did not affect
triglyceride concentrations. Thus, FS provided fewer
calories with the same degree of satiety as the higher
calorie intake of the control diet. FS may improve fullness at lower calorie intake during weight loss with no
effect on hypertriglyceridemia.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Body Condition and scFOS Supplementation Influence
Adipose Tissue mRNA Abundance
K.R. Belsito,a B.M. Vester,a F. Respondek,b M. Diez,c and K.S. Swansona,d,e
a
Department of Animal Sciences, University of Illinois, Urbana, Illinois
b
Béghin Meiji, Marckolsheim, France
c
University of Liège, Liège, Belgium
d
Division of Nutritional Sciences, University of Illinois, Urbana, Illinois
e
Department of Clinical Veterinary Medicine, University of Illinois, Urbana, Illinois
Adipose tissue is a highly active endocrine tissue that
plays a pivotal role in glucose and lipid metabolism,
energy homeostasis, and disease risk. Recent experiments suggest that fermentable dietary fibers, including short-chain fructooligosaccharides (scFOS),
may beneficially impact glucose homeostasis and
adipocyte metabolism. The objectives of the current
experiment were to compare adipose tissue mRNA
abundance in lean versus obese dogs and in obese
dogs fed a diet containing 1% scFOS versus a control
(fructan-free) diet.
The experiment consisted of two phases, the “obesity phase” followed by a “treatment phase.” Adipose
samples were collected from eight (four female, four
male) neutered adult beagles with a normal body
condition score (5 of 9) during fasted and fed states
at baseline. All dogs were then fed ad libitum to promote weight gain (to 125% optimal body weight)
and then fed to maintain this obese phenotype. In
the obese state, a crossover design was used to test
scFOS versus control diets. For each period, dogs were
randomly allotted to a diet and fed for 6 weeks. Fasting and fed adipose samples were collected at the end
of each period. Real-time quantitative reverse transcriptase polymerase chain reaction was used to measure mRNA abundance of genes involved with fatty
acid metabolism, glucose metabolism, or inflammation. mRNA data were analyzed using the mixedmodels procedure of SAS.
Compared with a lean phenotype, obesity increased (P < .05) insulin receptor substrate 2 and interleukin-6 mRNA abundance and tended to increase
(P < .10) leptin mRNA. In the obese state, scFOS altered the expression of hormone-sensitive lipase,
lipoprotein lipase, and uncoupling protein 2.
More research is needed to identify to what extent
gene transcripts or proteins involved with leptin or insulin signaling are affected by scFOS supplementation.
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All-Trans-Astaxanthin Does Not Protect Canine Osteosarcoma
Cells from Chemotherapeutic or Radiation-Induced Cell Death
J.J. Wakshlag, C.B. Balkman, A.M. Struble, S.K. Morgan, and M. Zgola
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York
Astaxanthin is a natural carotenoid with potent antioxidant properties in vitro and in vivo. Previous research in rodent models has suggested that
astaxanthin can diminish cell proliferation and retard
tumor growth. The exact mechanisms of action have
yet to be elucidated, but it is believed that astaxanthin can decrease promitogenic autocrine mediators,
inhibit cell signaling pathways, and alter cell adhesion molecules. Although astaxanthin may provide
an attractive alternative therapy for neoplasia, its
strong antioxidant capabilities have precluded its incorporation into cancer therapy, as it has been hypothesized that using antioxidants during radiation
or chemotherapy may hinder neoplastic cell death.
To test this hypothesis, we treated three osteosarcoma cell lines with and without radiation,
chemotherapy (doxorubicin), and peroxidative stress
(H2O2) to see if astaxanthin treatment significantly
alters cell death. Growth curves, cell death assays
(methyl thiazolyl tetrazolium), flow cytometry, and
soft agar growth assays were performed.
Astaxanthin treatment had no significant effects
on radiation or chemotherapeutic or peroxidative cell
death; however, it did significantly slow cell prolifer-
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Proceedings, 2007 Nestlé Purina Nutrition Forum
ation to various degrees in all three cell lines examined. To further elucidate the antioxidant capabilities
of astaxanthin-treated cells, we used a commercial kit
to measure total antioxidant potential of cell lysates,
which showed modest antioxidant potential; however, the antioxidant potential of astaxanthin-treated
cells was not enhanced beyond the natural upregulation of cellular antioxidant potential during cell
stress, further supporting our cell death assays.
Overall, the results suggest that astaxanthin has the
ability to significantly inhibit cell proliferation and
growth of colonies in soft agar but that this inhibitory
capacity is different, depending on the cell line examined, with no appreciable changes in cell cycle dynamics. Surprisingly, astaxanthin did not hinder the
ability of radiation treatment, peroxidation, or doxorubicin to induce cell death. This suggests that the
use of astaxanthin as a synergistic antiproliferative
compound may be beneficial in neoplastic diseases.
Further investigation into its use across various neoplasias and its mechanisms of action is warranted,
particularly because the antioxidant capabilities do
not seem to interfere with traditional cancer treatment options.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Absorption Trial of Ginkgo Biloba Extract in Cats
A. Pasquini,a G. Cardini,a C. Gardana,b P. Simonetti,b G. Giuliani,c G. Re,d and G. Lubasa
a
Department of Veterinary Clinic, University of Pisa, Pisa, Italy
b
Department of Food Science and Microbiology, Division of Human Nutrition, University of Milan, Milan, Italy
c
Urban Veterinary Hygiene, Florence, Italy
d
Bayer Italia, Milan, Italy
tive and quantitative evaluation of quercetin in
plasma at fixed times. Blood samples were collected
in heparinized tubes before EGb administration in
all four cats; after 1, 3, and 5 hours in two cats; and
after 5, 7, and 9 hours in the remaining two cats.
Plasma quercetin concentrations were established
without knowledge of study group by liquid chromatography tandem mass spectrometry.
Table 1 shows quercetin concentration in plasma
(ng/ml) in all four cats before and after the administration of EGb. Flavonoids from EGb were absorbed
by cats, and their main metabolite, quercetin, was
present in the blood for up to 5 hours. Furthermore,
none of the cats showed any adverse effects (e.g., diarrhea).
This evidence encourages the use of EGb, administered alone or added to the diet, to improve cat
wellness.
Ginkgo biloba extract (EGb) contains flavonoids,
which have antioxidant, antiinflammatory, and antiviral properties and induce peripheral vasodilation.
It is widely reported in the scientific literature that
these properties are useful for elderly humans and
animals. EGb can be administered to senior cats by
adding it to their food, which ensures regular and
continual administration. The presence of EGb
flavonoids in this study was confirmed by high-performance liquid chromatography coupled with a
diode array detector and mass spectrometry.
The goal of this study was to establish EGb
flavonoid absorption in cats. Four privately owned,
healthy cats of different sexes, ages, and breeds were
included in the study. The standardized EGb (glycosylated flavonoids: 24%; terpene lactones: 6%) was
administered at 20 mg/kg with 50 g of dry food
(Bayer Fito Progres Cat Senior®) followed by qualita-
TABLE 1
Quercetin Concentration in Plasma (ng/ml)
Cat
Time Zero
1 hr
3 hr
5 hr
7 hr
9 hr
1
0.0
0.0
6.67
4.47
No data
No data
2
0.0
7.15
11.28
0.0
No data
No data
3
0.0
No data
No data
0.0
0.0
0.0
4
0.0
No data
No data
0.0
0.0
0.0
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High-Protein Diet Impacts Fecal Microbial Populations
in Growing Kittens
a
B.L. Dalsing,a B.M. Vester,b C.J. Apanavicius,b D.C. Lubbs,b and K.S. Swansonb,c,d
Department of Molecular and Cellular Biology, University of Illinois, Urbana, Illinois
b
Department of Animal Sciences, University of Illinois, Urbana, Illinois
c
Department of Veterinary Clinical Medicine, University of Illinois, Urbana, Illinois
d
Division of Nutritional Sciences, University of Illinois, Urbana, Illinois
Although the intestinal microbiota of the human gut
has received considerable attention as of late, very little is known about life in the feline gastrointestinal
tract. Even less is known about the intestinal microbiota of growing kittens. Thus, our objective was to
investigate the intestinal microbiota of growing kittens fed moderate-protein (MP) or high-protein (HP)
diets using molecular qualitative and quantitative
techniques.
Kittens consuming an HP diet (7 males from 2 litters) or MP diet (10 males from 4 litters) were evaluated. Kittens were weaned at 8 weeks of age and
consumed the same diet as their dams. Fresh fecal
samples were collected at 8, 12, and 16 weeks of age
and stored at –80°C. Fecal DNA was extracted using
the QIAamp DNA Stool Mini-Kit (Qiagen, Valencia,
CA). DNA purity and concentration were determined
using an ND-1000 NanoDrop spectrophotometer.
Quantitative polymerase chain reaction (PCR) was
used to quantify four microbial groups (Bifidobacterium spp, Lactobacillus spp, Clostridium perfringens,
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Proceedings, 2007 Nestlé Purina Nutrition Forum
Escherichia coli) previously determined to be prevalent
in cats. Mixed models of SAS (Cary, NC) were used to
analyze quantitative PCR data. Qualitative analysis
was performed on each sample using denaturing gradient gel electrophoresis with a 29% to 48% gradient
to separate amplicons. DNA bands of interest were excised from the gel, extracted using the QIAquick Gel
Extraction Kit (Qiagen), and sequenced using an ABI
PRISM bigDye Terminator Cycle Sequencing Ready
Reaction Kit and ABI 3730XL capillary sequencer
(Applied Biosystems, Foster City, CA). 16S rRNA sequences were subject to BLAST search (GenBank) for
identification.
The presence of Bifidobacterium spp and Lactobacillus
spp was affected by diet, with kittens fed HP diets having lower (P < .05) counts than those fed MP diets. E.
coli was also lower (P < .05) in kittens fed HP diets and
was affected by age. Microbial differences in growing
kittens suggest that prebiotic supplementation may be
beneficial when feeding HP diets because of decreased
Bifidobacterium and Lactobacillus populations.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Impact of Sampling Interval on the Variability of Activity Counts
Recorded from the Actical Activity Monitor Worn by Pet Dogs
C. Dow, K.E. Michel, and D.C. Brown
University of Pennsylvania, Philadelphia, Pennsylvania
The Actical Activity Monitor (AAM; Mini-Mitter,
Bend, OR) is an accelerometer-based device that continuously measures movement for extended periods.
This device might permit quantification of activity
level and provide insight into the energy expenditure
of pet dogs. In validating the use of the AAM in pet
dogs, we wanted to determine the optimal sampling
interval for this population.
Fifty-five clinically normal dogs were included. After
obtaining the owners’ written consent and confirmation
of no planned changes in their usual schedule, dogs had
AAMs placed on collars around their necks. The collars
were worn continuously for 2 weeks. Between-dog and
day-to-day variability in activity counts that occurred
over the 2-week period were evaluated using ANOVA.
Weekdays and weekends were evaluated individually.
Activity counts in week 1 versus week 2 were compared
using paired t-tests to assess changes in the full 7 days as
well as weekday and weekend activity counts.
There was significant variability in activity counts
between dogs (P < .001). As a group, there was significant day-to-day variability in activity counts (P < .008),
which was driven by increased activity counts on
weekends compared with weekdays (P < .001). When
comparing the first and second weeks of data, fullweek and weekday activity counts were relatively stable (P = .31 and P = .44, respectively), but weekend
activity counts were less so (P = .07).
Full week-to-week comparisons of activity
showed no significant differences in counts in pet
dogs that maintain their normal routines. When
using the AAM to follow changes in groups of pet
dogs over time (e.g., before and after an intervention), comparing dogs on a full 7-day basis offers
the benefit of relatively stable estimates of activity in
unchanged animals while including the days with
the highest potential for changes in activity to occur
(i.e., weekends).
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Exercise Heart Rate and Blood Lactate Responses
as Indicators of Aerobic Capacity in Dogs
J.C. Bouthegourda and A.J. Reynoldsb
Nestlé Purina PetCare, Amiens, France
b
Nestlé Purina PetCare, Salcha, Alaska
a
The objective of this study was to quantify the intensity of different types of exercise by measuring heart
rate and blood lactate level in sled dogs to better understand their aerobic capacities.
Fourteen Alaskan huskies (seven males, seven females; age: 2.4 ± 0.4 years old; weight: 21.9 ± 0.9 kg)
were involved in mild (45-minute walk on leash),
moderate (2-hour trot at 8 mph), and intense (6minute run at 22 mph) exercise. Heart rate and activity intensity were measured using Actiheart
monitors (Mini-Mitter, Bend, OR) during the exercise, preexercise, and postexercise periods. Blood lactate was measured before and after exercise.
Average heart rates during mild, moderate, and
intense exercise were 159 ± 5.2, 179 ± 5.3, and
190 ± 2.7 bpm, respectively, and correlated with the
increase in measured activity: 246 ± 15 counts/min
(cpm), 454 ± 27 cpm, and 648 ± 27 cpm.
Preexercise lactate values for mild, moderate, and
intense exercise were 0.7 ± 0.1, 1.5 ± 0.2, and 1.3 ±
0.2 mmol, respectively. Postexercise lactate values
were low after mild and moderate exercise (0.8 ± 0.1
and 0.7 ± 0.1 mmol) but higher after intense exercise
(4.4 ± 0.7 mmol). By regression, we identified the lac-
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Proceedings, 2007 Nestlé Purina Nutrition Forum
tate threshold as being around 2 mmol, corresponding to 74% maximum heart rate. Walking and trotting
heart rates (64% ± 1.8% and 72% ± 2% maximum
heart rate, respectively) were beneath the lactate
threshold, indicating aerobic pathways as the main
supply of energy. Onset of blood lactate accumulation
(OBLA, 4 mmol) occurred at 76.5% maximum heart
rate. Intense exercise (77% ± 1% maximum heart rate)
was just beyond OBLA, indicating a large contribution
from anaerobic metabolic pathways.
The postexercise recovery times (time to recover
preexercise heart rate) were equivalent after mild and
moderate exercise but much higher after intense exercise (14 ± 2 and 15 ± 1 vs. 39 ± 2 minutes, respectively), reflecting the difference observed in
postexercise lactate values and the theoretical higher
oxygen debt after anaerobic intense exercise versus
aerobic mild to moderate exercise.
These results validate the use of Actiheart monitors in working dogs to evaluate the intensity of exercise. Together with blood lactate values, these
monitors give a clear picture of the scope of these
dogs’ aerobic capacity in response to different types of
exercise.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Effect of Different Dietary Protein Sources and
Carbohydrate Content on Canine Behavior
O. Pellegrini,a L. Casini,a V. Mariotti,b G. Lubas,c and D. Gattaa
Department of Animal Production, University of Pisa, Pisa, Italy
b
Department of Physiology, Cellular Biology and Immunology, Autonomous University of Barcelona, Barcelona, Spain
c
Department of Veterinary Clinic, University of Pisa, Pisa, Italy
a
The influence of some foods on the animal psychophysical equilibrium, outlining a direct connection between nutrition and animal behavior, is well
known. The purpose of this study was to evaluate the
effects of isoenergetic and isonitrogenous diets on animal behavior and health. The isoenergetic diet was
based mainly on vegetable proteins and was rich in
carbohydrates (soybean meal added), whereas the
isonitrogenous diet was based mainly on animal proteins and had a lower percentage of carbohydrates (respectively, dry matter: 91.5% vs 91.4%; protein: 27.0%
vs 29.9%; fat: 14.5% vs 29.4%; crude fiber: 4.2% vs
0.5%; ash: 6.1% vs 13.4%; carbohydrate: 50.0% vs
17.3%; metabolizable energy: 4,003 vs 4,213 kcal/kg).
After a careful history and clinical and laboratory
examinations confirmed good health and lack of evident behavioral disorders, 20 dogs (10 males, 10 females) weighing 10 to 30 kg and aged 1 to 7 years
were randomly assigned to one of the two diets. Dogs
were fed the individual diets for 40 days, including
30 days for the adaptation period and 10 days of observation. During the observation period, different
stressful situations were simulated (e.g., handling,
sudden light, loud noises, door opening). Each dog’s
behavioral reaction was evaluated by an expert behaviorist and divided into one of two categories: aggressive reactions and nonaggressive reactions.
Differences between the groups did not reach statistical significance; however, a trend toward hyperexcitability, with a consequent increase in aggressive
responses to some stimulations (e.g., sudden light:
P = .067; sudden opening of a door: P = .06; sight of
a cat: P = .070), was observed in dogs fed the animal
protein diet. These results suggest a possible benefit
(at the limit of statistical significance) of a vegetable
protein–based diet with a higher level of carbohydrates for reducing aggressive or excitable behavior
in dogs.
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Evaluation of Polymeric Diets Delivered Directly into the Small
Intestine through Surgically Placed Jejunostomy Tubes
S.A. Bone, F.A. Mann, R.C. Backus, and E. Kelmer
University of Missouri-Columbia, College of Veterinary Medicine, Columbia, Missouri
Polymeric diets in place of elemental diets are not recommended for jejunal feeding in human patients,
and at least one veterinary report recommends against
polymeric diets for animal patients. We tested the hypothesis that polymeric diets could be delivered directly into the jejunum without causing diarrhea.
A thorough examination of medical records in a
veterinary medical teaching hospital from 1999 to
2003 yielded 55 dogs and 6 cats that received at least
1 day of a polymeric diet administered directly into
the jejunum via a surgically placed jejunostomy tube.
Per hospital protocol, diluted diets were given in increasing strengths until full concentration was
achieved, typically on the third day of administration.
The liquid diet was discontinued when nutritional
support via oral intake was satisfactory. Diarrhea was
noted as a function of the presenting complaint, type
and duration of diet use, signalment, and survival.
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Proceedings, 2007 Nestlé Purina Nutrition Forum
Three commercially available diets were administered: CliniCare (Abbott Laboratories, Chicago, IL;
n = 40), Ensure Plus (Ross Laboratories, Columbus,
OH; n = 16), and Jevity (Ross Laboratories, Columbus, OH; n = 1); one group received a combination of
two of these diets (n = 4). Mean duration of use was
4.5 days (range: 1 to 13 days). The case of longest duration received concurrent Ensure Plus and Jevity
without developing diarrhea. Diarrhea occurred postoperatively in two dogs 1.5 and 6 days after initiation
of jejunal feeding, respectively. In one of these cases,
diarrhea was a presenting complaint. Forty-five animals survived, 11 died or were euthanized, and 5 had
incomplete follow-up.
Results of this study indicate that polymeric diets
delivered directly into the jejunum, although not formulated for that use, can be administered for postoperative nutritional support without causing diarrhea.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Seasonal Differences in Hair Growth between
Long-Haired and Short-Haired Cats
M. Hekman,a D.G. Thomas,a S.H. Moon,b and W.H. Hendriksc
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
b
Department of Animal Science, College of Natural Sciences, Konkuk University, Chungju, Korea
c
Animal Nutrition Group, Department of Animal Sciences, Wageningen University, Wageningen, The Netherlands
a
Hair growth in adult short-haired cats shows a strong
seasonal pattern, with maximal hair growth rates in
late summer and minimal rates in late winter. The
timing of the hair growth cycle is such that the densest and sparsest coats are produced during the coldest and warmest periods of the year, respectively. This
study aimed to investigate differences in hair growth
patterns between short- and long-haired domestic
cats.
Hair growth rates in 11 short-haired (8 male, 3 female) and 7 long-haired (2 male, 5 female) adult cats
1.4 to 6.8 years of age born at the Centre for Feline
Nutrition (Massey University, Palmerston North, New
Zealand) were determined throughout the year using
the midside patch technique.1 Cats from six litters
containing both long- and short-haired individuals
were used in this year-long study. Hair was shaved and
collected at monthly intervals and weighed before the
average diameter of the hair sample was measured
using an Optical Fibre Diameter Analyser (BSC Electronics, Attadale, Australia).
As previously reported, the midside hair growth rate
in short-haired cats showed a strong seasonal pattern.
Maximum hair growth occurred in late summer (273
μg/cm2/day), and minimum hair growth occurred in
late winter (29 μg/cm2/day). In contrast, the hair growth
rate in long-haired cats showed a less pronounced seasonal pattern, with an average maximum growth of 290
μg/cm2/day in late summer and an average minimum
growth of 100 μg/cm2/day in late winter. The average diameter of the coat samples showed that the short-haired
cats had coarser coats (28.54 μm in summer; 30.15 μm
in winter) than did the long-haired cats (24.13 μm in
summer; 17.37 μm in winter).
This study shows that long-haired cats grow more
hair during the year and show a less seasonal hair
growth pattern than short-haired cats, although the
timing of the hair growth cycle is similar.
REFERENCE
1. Hendriks WH, Tarttelin MF, Moughan PJ: Seasonal hair growth in
the adult domestic cat (Felis catus). Comp Biochem Physiol
1997;116(suppl A):29-35.
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Heritability of Hematology and Clinical Chemistry Variables
in Domestic Cats: What Are the Early Implications?
D.F. Lawler,a K. Chase,b R. Teckenbrock,a and K.G. Larkb
a
Nestlé Research Center, St. Louis, Missouri
b
Department of Biology, The University of Utah, Salt Lake City, Utah
Studies of human monozygotic and dizygotic twins
have documented quantitative genetic contributions
to phenotypic expression of clinical chemistry variables. We evaluated quantitative genetic aspects of
phenotypic expressions of erythrocyte, clinical chemistry, and acid–base measures in domestic cats (Felis
silvestris catus).
The metrics used for this study are part of a large
database that is maintained to support nutrition research. To establish single representation in the database for these analyses, sequential data over healthy
lifetimes of individual cats were expressed as the
mean overall lifetime analyses for each chosen variable. This procedure made available data from 564
cats for erythrocytic metrics, 444 to 530 cats for serum
clinical chemistry, and 629 cats for venous acid–base
metrics. Extreme (nonphysiologic) values were removed, and non-normal traits were log-transformed.
The “polygenic” function of SOLAR (sequential oligogenic linkage analysis routines) was used to estimate heritability as the ratio of additive genetic
variance to total variance. This procedure estimates
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Proceedings, 2007 Nestlé Purina Nutrition Forum
additive genetic variance by relating the additive genetic relationship matrix (2x coefficient of coancestry
between pairs) to the phenotypic covariance. Multiple regression techniques were used to adjust for diet
within nutrition study in the database. Inbreeding in
this colony was minimal.
Heritabilities for erythrocyte, clinical chemistry,
and acid–base variables ranged, respectively, between
0.41 and 0.69, 0.13 and 0.78, and 0.23 and 0.59 (P
< .05). Some observations merit additional comment.
The high heritability of the serum alkaline phosphatase phenotype likely explains frequently observed smaller disease-related responses in cats
compared with other species. However, the quantitative genetic signals that were recognized for venous
acid–base metrics were quite surprising.
The physiologic implications of similar heritabilities among species for the same variable may be different, dictating caution with interspecies phenotypic
comparisons. Minimally, these data indicate that differential heritability of clinical chemistry metrics
should be considered in health screening.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Thyroid Hormone Concentrations and Prevalence
of Thyroid Pathology in Geriatric Cats
C. Cupp and W. Kerr
Nestlé Purina Research, St. Louis, Missouri
Hyperthyroidism is a common problem in geriatric
cats. As part of a larger study of aging in cats, we examined the effect of age on thyroid hormone (T4)
concentrations as well as the prevalence of thyroid
pathology postmortem.
Fifty-nine cats ranging in age from 8 to 15 years
old (average age: 11.6 ± 2.3 years old) at the start of
the study were evaluated for up to 7 years. The cats
had no evidence of hyperthyroidism based on baseline T4 concentration or physical examination. T4 levels along with other routine health parameters were
evaluated and physical examinations performed periodically until the cats’ natural deaths (average age of
death: 15.4 years). After each cat’s death, a full
necropsy was performed and both thyroid glands
were submitted for histopathology.
Twenty-one cats (35.6%) had evidence of thyroid
hyperplasia or adenoma on histopathology. Of these,
only seven cats exhibited serum T4 levels above the
reference range at some point during the preceding
years (average age at diagnosis: 14.8 ± 2.3 years). Four
of the seven cats were diagnosed with hyperthyroidism by physical examination, clinical signs, and
consistently elevated T4 levels. Aging had no significant effect on serum T4 level in this study; however, a
difference between cats with hyperthyroidism (as evidenced by histopathology) and those without hyperthyroidism was noted (P = .097). Among cats that
developed thyroid disease, T4 levels gradually increased over time (P = .055); nonhyperthyroid cats
showed no change with age.
In conclusion, serum T4 level tends to increase
with age in cats with thyroid pathology but does not
change in cats without thyroid pathology. Based on
these data, a consistent increase in T4 level over time
strongly suggests developing thyroid disease, but a
large number of cats with thyroid disease have T4 levels within the reference range.
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Age-Related Changes in Immune Function in Cats
K.J. Rutherfurd-Markwick,a M.C. McGrath,a R.H. Morton,a P.C.H. Morel,a and W.H. Hendriksb
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
b
Animal Nutrition Group, Department of Animal Sciences, Wageningen University, Wageningen, The Netherlands
a
Many species show a similar decline in immune function with age; however, little research has been done
in cats. The goal of this study was to extend the information available on age-related changes in immune function in domestic cats and to compare our
results with those previously reported.
The study was conducted at the Centre for Feline
Nutrition at Massey University in Palmerston North,
New Zealand, over a 28-day period. Whole-blood
samples were collected from 138 domestic shorthaired cats (71 male, 65 female) aged 7 months to
13.5 years. The cats were fed a variety of commercial moist foods (approved by the Association of
American Feed Control Officials), with water freely
available.
Samples were analyzed for expression of cell surface markers (CD4+ cells, CD8+ cells, B cells,
CD11b+ cells), phagocytic activity, and mitogen-induced lymphocyte proliferation (concanavalin A
[ConA], phytohemagglutinin antigen [PHA]). Agerelated trends were assessed by simple linear regression analysis. Detailed family trees were available,
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Proceedings, 2007 Nestlé Purina Nutrition Forum
and hereditary effects on immune function parameters were also determined.
Results showed a significant (P = .0001) age-related
decline (R2 = .25) in the phagocytic activity of peripheral blood leukocytes. There were no age-related trends
in the relative percentages of T-helper cells (CD4+), cytotoxic T cells (CD8+), or granulocytes (CD11b+).
There was a decline (P = .02) in the relative percentage
of B cells and a decrease (P = .011) in lymphocyte-proliferative responses to stimulation with ConA with age;
however, no change in lymphocyte blastogenic responses to PHA was observed. Parentage, particularly
the father, had significant effects on phagocytic activity, percentages of CD8+ cells, CD4:CD8 ratio, and
lymphocyte-proliferative responses to ConA.
Unlike other studies, we did not see significant
changes in the level of expression of CD4+, CD8+, or
CD11b+ cells or proliferative responses to PHA, possibly due to the age range or the genetic profile of the
population studied. Decreases in both percentage of
B cells and proliferative response to ConA were similar to those previously reported.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Effect of Dietary Form on Nutrient Digestibility
in Cats and Dogs
K. Weidgraaf, S.M. Rutherfurd, K.A. O’Flaherty, D.G. Thomas, and K.J. Rutherfurd-Markwick
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
In vivo methods for determining the digestibility of
companion animal diets generally involve either total
fecal collection or using an indigestible marker. The
total fecal collection method is labor-intensive and
prone to sample losses. Therefore, using indigestible
markers is generally preferred, particularly in dogs.
When using indigestible markers, the diet must be
ground to facilitate the homogeneous mixing of the
marker into the diet; however, little work has been
done to investigate whether this change in dietary
form has any effect on digestibility.
A preliminary study was carried out to compare
the nutrient digestibility of two different forms of a
dry diet (unground vs ground) in cats and dogs. Eight
male cats (3 to 7 years of age) from Massey University’s Centre for Feline Nutrition were fed a dry Association of American Feed Control Officials (AAFCO)–
approved diet in either ground or unground form. In
a crossover design, the cats received each diet for 12
days, which included a 7-day adaptation period followed by a 5-day total fecal collection period. The
diet was fed according to maintenance requirements,
and water was available ad libitum. Feed intake and
fecal output were measured. Feces from each cat were
subsampled, freeze-dried, and analyzed for gross energy and protein.
Similarly, six male and six female dogs (3 to 8
years of age) from Massey University’s Canine Unit
were fed either ground or unground AAFCO-approved dog biscuits for a total of 12 days. Sample collection, preparation, and analysis were also carried
out as described in the feline study. Preliminary data
showed no difference in digestibility between the
ground and unground diets in cats (respectively, energy: 86.4% vs 86.7%; protein: 82.7% vs 82.8%). In
dogs, however, dietary form did appear to affect digestibility (respectively, energy: 82.81% vs 84.3%;
protein: 78.2% vs 80.1%).
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Chemical Composition and In Vitro Crude Protein and Fiber
Disappearances of Corn Coproducts from the Ethanol Industry
M.R.C. de Godoy, L.L. Bauer, and G.C. Fahey, Jr.
Department of Animal Sciences, University of Illinois, Urbana, Illinois
The objective of this study was to determine the
chemical composition and protein and fiber disappearances of corn protein concentrates (CPC1, CPC2)
and corn fiber (CFn), novel coproducts from the
ethanol industry, compared with conventional plant
protein and fiber ingredients used in the pet food industry. Novel corn coproducts were produced from a
pilot modified wet milling plant.
Crude protein values for CPC1 and CPC2 were
57.3% and 49.7%, respectively. Total dietary fiber was
29% for CPC1 and 23.5% for CPC2. Acid hydrolyzed
fat and gross energy were similar for these ingredients. Crude protein disappearance after 6 hours of incubation in an HCl/pepsin solution was highest for
soybean meal (SBM) (53.3%), followed by corn
gluten meal (CGlM) (49.3%), distillers dried grains
with solubles (DDGS) (49.0%), CPC2 (29.3%), corn
germ meal (CGeM) (25.3%), and CPC1 (24.9%).
After an additional 18 hours of incubation (24 hours
total) with porcine pancreatin, CGlM had the highest
corn protein disappearance (94.1%), followed by
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Proceedings, 2007 Nestlé Purina Nutrition Forum
SBM (87.2%). CPCs had corn protein disappearances
of 77.5% (CPC2) and 74.1% (CPC1).
Crude protein concentration ranged from 0%
(Solka Floc [SF]; International Fiber Corporation, St.
Louis, MO) to 11.0% (CF control 1 [CFC1]). Total dietary fiber was highest for SF (100%) and lowest for
beet pulp (68.8%). Corn fibers had intermediate total
dietary fiber values. Acid hydrolyzed fat concentrations ranged from 0.8% (SF) to 6% (CFC1). Gross energy values were very similar among corn fiber
sources. Organic matter disappearance was lowest for
SF in the hydrolytic (–6.5%) and fermentative stages
(–2.1% and –1.6% at 8 and 16 hours, respectively)
and highest for CFC1 and beet pulp in the hydrolytic
stage. Beet pulp was the only fiber source with significant fermentation (17.7% after 16 hours). CFC1
and CFC2 had intermediate fermentation values
(5.7% and 5.3%, respectively), but CFC1 and CFC2
were higher than CFn (3.0%). Substrate versus time
interactions were significant (P < .05) for organic
matter disappearance.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Corn Fiber Effects on Nutrient Digestibility and Fecal
Characteristics of Dogs
M.A. Guevara,a L.L. Bauer,a C.A. Abbas,b K.E. Beery,b M.A. Franklin,b M.J. Cecava,b and G.C. Fahey, Jr.a
a
Department of Animal Sciences, University of Illinois, Urbana, Illinois
b
Archer Daniels Midland Company, Decatur, Illinois
Understanding the impact of different processing
methods in the manufacture of fiber-rich corn coproducts is a precondition of their potential use as
fiber sources for dogs. This experiment examined
total tract nutrient digestibility and fecal characteristics of adult dogs fed selected fiber-rich corn coproducts from the ethanol industry.
Native corn fiber (NCF), NCF with fines, hydrolyzed corn fiber (HCF), and hydrolyzed extracted
corn fiber (HECF) were included as fiber sources in a
commercial-type diet matrix with poultry byproduct
meal and brewer’s rice as the main ingredients and
chromic oxide (0.2%) included as a digestion marker.
Beet pulp (BP) was used as a positive control treatment.
Diets were fed to 15 beagles in a partially balanced
incomplete block design with two blocks of 12 days,
including 8 days for diet adaptation and 4 days for
fecal collection.
The average daily food intake, fecal production, fecal
scores, and fat and crude protein digestibilities were not
significantly different among treatments. Body weight
and body condition score remained unaltered throughout the duration of the experiment. Apparent dry matter (DM) digestibility coefficients were high, with the
NCF treatment having a small but statistically higher
value compared with the remaining treatments except
for the NCF with fines. Dogs fed BP, HCF, and HECF
had lower DM digestibilities compared with those fed
NCF but not compared with dogs fed NCF with fines.
Apparent total dietary fiber digestibility was higher for
NCF, BP, and HECF treatments, but BP and HECF were
no different than NCF with fines and HCF treatments.
Results of this experiment suggest that incorporation of corn fibers at the 7% inclusion level, when
substituted for BP in diets of healthy adult dogs, does
not dramatically impact nutrient digestibility, food
intake, or fecal characteristics.
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In Vitro Evaluation of Protein Digestibility of Four Pet Foods
F. Bovera, S. Calabrò, S. D’Urso, R. Tudisco, A. Guglielmelli, R. Romano, and M.I. Cutrignelli
Dipartimento di Scienze Zootecniche e Ispezione degli alimenti, Università degli Studi di Napoli “Federico II,”
Via F. Delpino, Napoli, Italy
Given the need to develop in vitro methods to simulate digestion of pet food, we carried out an investigation to examine the proteolytic activity of
Streptomyces griseus protease to determine its suitability to estimate protein digestibility for dogs.
In vitro protein digestibility was measured (according to work by Coblentz and coworkers1) on four
dry concentrates for large-breed puppies using S.
griseus protease (sigma EC 3.4.24.31). Residual crude
protein was determined after 0, 24, and 48 hours of
incubation.
Protein losses at time 0, without incubation, corresponded to the soluble protein fraction. The chemical composition results were similar among the pet
foods (average values for crude protein: 27.5 ± 1.27;
ether extract: 11.6 ± 3.99; crude fiber: 3.54 ± 0.62 %).
The ranking of pet foods for soluble protein (time 0)
was 1 and 4 > 2 > 3 (P < .01). At 48 hours, pet food
3, which was characterized by the lowest soluble pro-
TABLE 1
Protein Digestibility in Tested Pet Foods (%)
Pet Food
Time 0
24 hr
48 hr
1
65.0A ± 0.05
28.1 ± 0.40
6.55Bb ± 0.75
2
51.3 ± 1.06
26.7 ± 0.57
11.4 ± 1.02
3
27.3C ± 0.88
27.9 ± 0.56
25.2A ± 0.59
4
62.7A ± 0.11
28.9 ± 0.84
8.47B ± 0.46
B
A, B, C = P < .01; a, b, c = P < .05.
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Proceedings, 2007 Nestlé Purina Nutrition Forum
a
tein value, showed the highest digestibility (Table 1).
These results correspond with previous data obtained in vivo in a growing trial conducted on 24 German shepherd puppies2 in which pet foods 1 and 4
allowed significantly (P < .01) higher weight gains
from the age of 60 days. In each case, all registered
daily weight gains (from 66 to 93 g/d and from 93 to
150 g/d in the period 1 to 60 days and 60 to 90 days,
respectively) are included in the ranges indicated by
Debraekeleer and coworkers3 for the periods 1 to 2
and 3 to 5 months of age in puppies with an average
adult body weight of 30.5 kg. Considering the insufficient enzymatic production and development of gut
microbial population in the period immediately after
weaning, the availability of soluble protein, which is
immediately absorbable and utilizable, could improve nutrient availability.
These preliminary results demonstrate the validity
of this rapid and reliable in vitro procedure in estimating the protein digestibility of dog foods.
REFERENCES
1. Coblentz WK, Abdelgadir IE, Cochran RC, et al. Degradability of
forage proteins by in situ and in vitro enzymatic methods. J Dairy
Sci 1999;82:343-354.
2. Cutrignelli MI, D’Urso S, Solimene R, et al. Influence of feeding
programme on growth dynamics of German shepherd puppies
until 3 months of age. Proc 10th Congr Eur Soc Vet Comparative
Nutr:76, 2006.
3. Debraekeleer J, Gross KL, Zicker SC. Normal dogs. In: Hand MS,
Thatcher CD, Remillard RL, Roudebush P, eds. Small Animal Clinical Nutrition. 4th ed. Topeka, KS: Mark Morris Institute; 2000:213260.
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RESEARCH ABSTRACTS: POSTER PRESENTATION
Review of Pet Dog Feeding Habits in Spain
V.M. Mariotti, M. Hervera, J. Fatjó, M. Amat, M.D. Baucells, and X. Manteca
Animal Nutrition, Management and Welfare Research Group, Department of Animal and Food Science,
Autonomous University of Barcelona, Catalonia, Spain
Little epidemiologic data exist about pet dog feeding
habits and management in Europe.1–3 Studies show
that feeding patterns, environmental conditions, and
pet management all affect animal health, behavior,
and welfare.4,5 Between 1995 and 2005, a retrospective
epidemiologic study was carried out to analyze trends
in feeding habits of pet dogs in Catalonia, Spain. The
specific goals this study were to determine (1) the effect of environmental factors on the dogs’ feeding
habits as well as (2) the relationship between the type
of food provided and the composition of the family.
A total of 1,000 dogs (Canis familiaris) were observed for the purpose of behavioral and clinical evaluation at the Clinical Behavioral Service of the
Veterinary Teaching Hospital of the Autonomous
University of Barcelona. Recorded information included sex, age, breed, type of food (dry, wet, mixed),
mode of administration (meal fed, free choice), family composition (family size and age, presence of children or other pets in the home), environment
(apartment or house, urban or rural location, presence of a garden or terraces), exercise (walk frequency
and duration), and behavioral problems. To determine the relationship between dietary habits and
management and behavioral problems in the dogs,
data for 500 dogs were analyzed by chi-square test
(SPSS 12.0). Study results indicate that the most common types of food consumed were medium- to highquality dry foods (74%) fed twice daily. The typical
owner in the study was a young couple with no children (45%) living in an apartment (>80%).
Some management and dietary characteristics
were found to be related to canine behavioral problems and welfare. Free-choice dogs showed less foodrelated aggression toward family members than
meal-fed dogs (P < .05). This could be because when
food is continuously available, dogs perceive it as a
less valuable resource than when it is offered only a
few times a day. Moreover, it appears that there is a
relationship between dog environment and separation anxiety: dogs with more available space when
alone show less anxiety than dogs living in a little
room (P = .001).
Dog management (i.e., exercise level, including
frequency and duration of walks) and aggressive behavior toward family members could be related: dogs
with a reduced exercise level (0 or 1 walk/day) were
more aggressive toward family members than dogs
with a higher exercise level (3 or 4 walks/day; P =
.05). This result could be partially explained by the
increase in serotonin turnover caused by regular exercise, as shown in humans and other species.6,7
This preliminary study suggests that diet, feeding
pattern, and management may play a role in the development of behavior problems in dogs.5,8,9
REFERENCES
1. Freeman LM, Abood SK, Fascetti AJ, et al. Disease prevalence
among dogs and cats in the United States and Australia and proportions of dogs and cats that receive therapeutic diets or dietary
supplements. JAVMA 2006;229(4):531-534.
2. Lund EM, Armstrong PJ, Kirk CA, et al. Health status and population characteristics of dogs and cats examined at private veterinary
practices in the United States. JAVMA 1999;214(9):1336-1341.
3. Patronek GJ, Beck AM, Glickman LT. Dynamics of dog and cat
populations in a community. JAVMA 1997;210(5):637-642.
4. Fernstrom JD. Dietary amino acids and brain function. J Am Diet
Assoc 1994;94:71-77.
5. Houpt KA, Zicher S. Dietary effects on canine and feline behaviour. Vet Clin North Am Small Anim Pract 2003;33:405-416.
6. Chaouloff F, Laude D, Elghozi JL. Physical exercise: evidence for
differential consequences of tryptophan on 5-HT synthesis and metabolism in central serotonergic cell bodies and terminals. J Neural
Transm 1989;78:121-130.
7. Dey S, Singh RH, Dey PK. Exercise training: significance of regional alterations in serotonin metabolism of rat brain in relation
to antidepressant effect of exercise. Physiol Behav 1992;52(6):
1095-1099.
8. Dodman NH, Reisner I, Shuster L, et al. Effect of dietary protein
content on behavior in dogs. JAVMA 1996;208:376-379.
9. DeNapoli JS, Dodman NH, Shuster L, et al. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. JAVMA
2000;217(4):504-508.
Supplement to Compendium: Continuing Education for VeterinariansTM Vol. 30, No. 3(A), March 2008
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Use of a Wireless Multisensor Telemetry Capsule for
Monitoring the Canine Gastrointestinal Tract
W.A. Anderson, W. Kerr, and G. Mohr
Nestlé Purina PetCare Research, St. Louis, Missouri
The SmartPill GI Monitoring System (SmartPill Corporation, Buffalo, NY) provides ambulatory testing
for gastrointestinal (GI) tract pressure, temperature,
and pH; gastric emptying time (GET); combined small
and large intestine transit time; and total GI transit
time. This device, although extensively tested in humans, had not been previously evaluated in dogs. The
objective of this study was to evaluate the feasibility of
measuring GI transit time and gastric pH in dogs.
Eight (four male, four female) clinically healthy
Labrador retrievers were used in the study. After an 8to 10-hour fast, the dogs were fed one-third of their
daily energy requirement. The capsule was administered immediately after food consumption (time 1
[T1]). The dogs were fitted with mesh jackets with
pockets to hold the data receiver and then returned to
their runs. The dogs were monitored until the unit
was expelled in the feces (time 2 [T2]), and total GI
transit time was defined as time from T1 to T2. Gastric emptying time was measured from T1 until the
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Proceedings, 2007 Nestlé Purina Nutrition Forum
onset of a sudden and sustained increase of at least 3
pH units above baseline. Small and large intestine
transit time was calculated as total GI transit time
minus gastric emptying time.
The capsule was successfully administered to and
retrieved from the stools of all dogs. There was a difference (P < .05) in gastric emptying time between
sexes, averaging 15.17 hours for females versus 12.58
hours for males. The average small and large intestine transit times were 18.77 hours for females and
21.84 hours for males, and the average total GI transit times were 33.45 hours for females and 34.29
hours for males. The mean gastric pH was 2.14 for females and 2.34 for males.
From the results of this study, we can conclude that
the SmartPill technology is a novel, noninvasive
method for assessing several aspects of GI function.
This technology has the potential for clinical and research applications to study the effect of diet or nutrients on the canine GI tract.
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