Comparative Medicine
Copyright 2005
by the American Association for Laboratory Animal Science
Vol 55, No 5
October 2005
Pages 445-451
Noninvasive Measures of Body Fat Percentage in
Male Yucatan Swine
Carol A. Witczak,1,3 Eric A. Mokelke,1,3,5 Robert Boullion,1,3 James Wenzel,1,3 Duane H. Keisler,4 and Michael Sturek1-3,5,*
The purpose of this study was to assess the use of body circumference, ultrasonography, and serum leptin levels
as noninvasive measures to estimate body fat percentage in adult, male, Yucatan swine, which are widely used in
biomedical research models. Swine (ages, 8 to 15 months) were maintained for 20 weeks: control (n = 7); high-fat,
high-cholesterol diet (hyperlipidemic; n = 8); alloxan-induced diabetes with high-fat, high-cholesterol diet (diabetic
dyslipidemic; n = 7); and diabetic dyslipidemic plus exercise-trained (n = 6). Anesthetized swine were positioned on
their dorsum for the following measurements: 1) neck, mid-abdomen, and widest abdominal girth circumferences;
and 2) neck and mid-abdomen ultrasound measurements. Blood samples were obtained for quantification of serum
leptin levels. After euthanasia, the carcass and viscera were separated for chemical composition analysis, which demonstrated a significant increase in carcass and visceral fat in the diabetic dyslipidemic swine compared to controls.
Serum leptin levels were also increased in the hyperlipidemic and diabetic dyslipidemic swine. Regression analyses
demonstrated a significant correlation between carcass fat, visceral fat, and all of the circumference, ultrasound, and
serum leptin measures. In conclusion, the widest abdominal girth circumference was the noninvasive measure with
the highest predictive value for estimating carcass and visceral fat in adult, male Yucatan miniature swine.
The Yucatan miniature swine model has been extensively used
for the study of human cardiovascular and metabolic disorders
(3, 11, 14, 17, 19, 22, 23, 25-28, 33, 34). The many similarities to
human features, including cardiac and coronary anatomy and
diet-induced atherosclerosis, make the use of this model highly
compelling (7, 17, 26, 27, 34). Despite the widespread use of this
model, there surprisingly are no reports on the alterations that
occur in body composition as a result of dietary-induced hyperlipidemia, chemical (alloxan)-induced hyperglycemia, or treadmill
exercise training interventions routinely used in Yucatan swine.
The quantification of body fat is an essential component of any
study that assesses physiologic responses to metabolic disorders
such as obesity and diabetes (30). Unlike human studies, animal
studies can use invasive, terminal procedures (i.e., direct chemical composition analysis) in order to obtain the most accurate
assessment of body composition. In commercially bred animals,
the ability to predict body fatness and leanness noninvasively is
crucial to assessing carcass yield and quality, and for the selection of traits for breeding (31). The validity of noninvasive measures has been established for commercial swine, but predictions
of body fat from these same noninvasive measures do not hold
for miniature feral swine (32).
The utility of having a noninvasive technique that accurately
could predict body fat percentage in swine models for biomedical research would be the ability to obtain serial measurements
throughout a study while minimizing the number of animals
used. In human studies, a number of noninvasive techniques
have been used for the assessment of body composition, includReceived: 3/21/05. Revision requested: 7/26/05. Accepted: 7/27/05.
Departments of Medical Pharmacology & Physiology1, Internal Medicine2, and the
Center for Diabetes & Cardiovascular Health,3 School of Medicine, Department
of Animal Sciences,4 School of Agriculture, University of Missouri, Columbia,
Missouri; Department of Cellular & Integrative Physiology,5 Indiana University
School of Medicine, Indianapolis, Indiana
*Corresponding author.
ing anthropometry (i.e., body circumference), ultrasonography,
water immersion, computed tomography, nuclear magnetic resonance imaging, total body electrical conductivity, electrical impedance, and infrared interactance (4, 16, 30). However because
most of these techniques require expensive and cumbersome
equipment, in the current study we focused on the use of body
circumference and ultrasonography to assess body fat in miniature Yucatan swine.
Leptin is a cytokine-like protein that is involved in the regulation of body fat in humans (10, 20, 30). Recent studies in both humans (21) and animals (5) have demonstrated direct correlation
between circulating leptin levels and body fat. Because of this
direct connection, we also assessed whether serum leptin levels
were tightly correlated with alterations in body fat percentage
in Yucatan swine.
Therefore, the primary purpose of this study was to assess the
use of body circumference measurements and ultrasound measurements of subcutaneous fat thickness as noninvasive measures to estimate body composition in the Yucatan swine models
of hyperlipidemia, diabetic dyslipidemia, and exercise training.
In addition, the relationship between serum leptin levels and
body fat was examined to assess this aspect of fat metabolism in
these swine. Our results indicate that noninvasive methods can
be used to estimate body fatness in young adult male miniature
Yucatan swine.
Materials and Methods
Yucatan models of hyperlipidemia and diabetes. All procedures involving animals were approved by the University of
Missouri Animal Care and Use Committee and complied fully
with the Guide for the Care and Use of Laboratory Animals (24).
Male, Yucatan miniature swine (Sus scrofa domestica) were
bred at the Sinclair Research Center (Columbia, Mo.). The Sinclair Research Center is a licensed breeder with the U.S. De-
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Comparative Medicine
October 2005
partment of Agriculture (43-R-2499) and is accredited by the
Association for Assessment and Accreditation of Laboratory
Animal Care, International. The colony is free of brucellosis and
pseudorabies. The breeding colony is routinely vaccinated for parvovirus, leptovirus, Bordetella pertussis, swine influenza virus,
tetanus, and Actinobacillus (Haemophilus) pleuropneumoniae
and has quarterly treatment for parasite prevention by alternation between ivermectin and levamisole. All pigs used in the
present study were vaccinated for Clostridium perfringens types
C and D, A. pleuropneumoniae, Salmonella typhimurium, and S.
choleraesuis and received ivermectin for parasite prevention.
Swine were obtained at 8 to 15 months of age and transferred
to the Laboratory Animal Care Facility at the University of
Missouri, School of Medicine. The average age of the pigs was
12 months, and there were no differences in age between the
groups. Swine were housed individually in 2.3 m2 pens with expoxy-sealed concrete floors in rooms maintained at 21 to 27°C on
a 12:12-h light:dark cycle. Swine were randomly assigned to one
of four treatment groups: low-fat diet, sedentary (control, n = 7);
high-fat, high-cholesterol diet (hyperlipidemic, n = 8); alloxaninduced diabetes plus high-fat, high-cholesterol diet (diabetic
dyslipidemic, n = 7); and alloxan-induced diabetes, high-fat highcholesterol diet, and aerobic exercise-trained (diabetic dyslipidemic plus exercise, n = 6). The low-fat diet consisted of Purina
Minipig chow (Purina Mills Inc., St. Louis, Mo.). The low-fat-fed
animals were maintained at their normal weight gain of ∼1.0%
weekly (3). The high-fat, high-cholesterol diet consisted of 1000
g Purina Minipig chow supplemented with 14.0 g cholesterol,
119.7 g coconut oil, 16.1 g corn oil, 4.9 g sodium cholate, and
241.8 g sucrose (3, 7, 14, 34). The diabetic dyslipidemic, hyperlipidemic, and exercise-trained animals were maintained at a 3%
weight gain weekly by increasing food amounts as needed (3).
All animals were fed individually once daily and were given free
access to water.
Alloxan-induced diabetes and fasting blood glucose
levels. Diabetes was induced by intravenous administration
of 100 mg/kg of the pancreatic beta cell toxin alloxan (3, 7, 14,
23, 25, 34). Diabetic pigs were maintained with plasma glucose
levels at 300 to 400 mg/dl for the duration of the study. Feed
and insulin algorithms were used to maintain positive energy
balance in all experimental groups (3). Fasting blood glucose
measurements were obtained in fully conscious, unanesthesized
swine via ear veins punctures and Accucheck blood glucose monitors (Boehringer-Ingelheim Corp., North Chicago, Ill.).
Treadmill exercise training and heart-rate assessment
protocols. Diabetic dyslipidemic swine were acclimated to a
motorized treadmill (Good Horsekeeping, Inc., Ash Grove, Mo.)
for 2 weeks, during which the grade and speed were increased in
small increments as previously described (3). Exercise training
consisted of treadmill running performed 4 days per week for
16 weeks. The training bout consisted of four stages: 1) 5-min
warm-up at 35-40% of maximum heart rate, 2) 5 min at 40-50%
of maximum heart rate, 3) 30 min at 65-75% of maximum heart
rate, and 4) a 5-min cool-down at 35-40% of maximum heart rate.
Heart rates were determined just prior to the exercise bout and
at the middle and end of stage 3.
To assess pre-, mid-, and postexercise heart rates, fully conscious, unaesthetized swine were transferred from pens to the
motorized treadmill. Once the animals were on the treadmill,
pre-exercise heart rates were obtained by placing a stethoscope
446
to the chest wall of the pig and counting heart beats for 1 min.
After this step, the exercise bout commenced. To obtain the heart
rates at the middle and end of stage 3, the treadmill was briefly
stopped, and the stethoscope was positioned carefully on the
chest of the pig. Heart beats were counted for 1 min. Throughout
the training period, training intensity was maintained in the
desired heart rate range by altering the treadmill grade.
Efficacy of training was verified by a decrease in resting heart
rate and increased tolerance to increasing treadmill grade (3).
After 16 weeks of training, each animal was placed in a lowstress sling, and six-way electrodes were attached to the chest
to obtain an electrocardiogram recording. After the animals had
a 10-min acclimation period in the sling, 8 to 10 1-min intervals
were analyzed for heart rate during a 10-min recording phase.
These values were averaged together to determine the resting
heart rate for each animal. The animals did not exercise for 2
days prior to euthanasia, to separate the acute effects of exercise
from the chronic effects of training.
Anesthesia. Swine were anesthetized by an intramuscular
injection of 0.05 mg/kg atropine, 6.6 mg/kg telazol, and 2.2 mg/kg
xylazine; the level of anesthesia was maintained with isoflurane
gas (1 to 3%). Swine were positioned on their dorsums for experimental measurements and blood sampling for leptin assays.
Circumference measurements. For circumference measurements, anesthetized animals were positioned on their dorsums by using a custom-made stabilizing board. The apex of the
sternum was used as an anatomical reference point for the standardization of neck and abdominal circumference measurements
between animals. The apex of the sternum was defined as the
highest point of the breastbone when the pig was restrained on
its dorsum.
By using a flexible, plastic measuring tape, circumference measurements were obtained at the following three positions: 1) ventral neck, 2) mid-abdomen, and 3) widest abdominal girth. From
the apex of the sternum, the ventral neck location was defined as
20 cm cranial along the central axis of the pig; the mid-abdomen
location was defined as 30 cm caudal along the central axis of the
pig. The widest girth circumference measurement was defined as
the largest circumference measurement around the abdomen of
the pig. A graphic depiction of the anatomic sites is provided in
Fig. 1. Because each pig was fully anesthetized when circumference measurements were performed, accurate measurements
were obtained with one or two attempts at each site.
Ultrasound measurements of subcutaneous fat. Immediately after the circumference measurements, ultrasound
images were obtained at the neck and mid-abdomen locations
for off-line analysis of subcutaneous fat thickness. A Biosound
AU3 (Biosound Easoate, Inc., Indianapolis, Ind.) high-resolution
ultrasound system was used to obtain two-dimensional images
with a linear 2.0-MHz probe and scanning depths of 4 and 10
cm. The ultrasound probe was placed at the intersection of the
central axis and either the ventral neck location or the mid-abdomen location for measurements of ventral neck subcutaneous
fat or mid-abdomen subcutaneous fat, respectively. The choice of
these anatomic coordinates enabled us to easily locate the same
position on every animal used in the study. Off-line analysis was
performed using the Biosound software package (version 6.0,
Biosound Easoate, Inc., Indianapolis, Ind.), whereby ‘electronic
calipers’ were used to digitally measure the thickness of the subcutaneous fat layer. To confirm the validity of the subcutaneous
Body fat in Yucatan swine
Figure 1. Anatomical locations used for the assessment of circumference and subcutaneous fat thickness in male, Yucatan miniature pigs.
The apex of the breastbone was used as an anatomical landmark to
normalize the ventral neck and mid-abdomen locations at 20 cm cranial
and 30 cm caudal, respectively. The widest girth location was defined as
the largest circumference around the abdomen. This location was found
at a variable distance from the top of the breastbone.
fat measurements, we removed an 8 × 2 × 3 cm (length × width ×
height) section of tissue from a subgroup of animals. Ultrasound
images were obtained from this section of carcass to validate the
measurements that were obtained from the intact animal.
Serum leptin analysis. Blood samples for serum leptin assays were collected from overnight-fasted swine while they were
under isoflurane anesthesia, and the serum was assayed for
leptin levels as described previously (2). Briefly, standard concentrations of ovine leptin were added to assay tubes in quadruplicate and the total volume balanced to 300 μl per tube with
PABET buffer (0.1% gelatin, 0.01 M ethylenediaminetetraacetic acid, 0.9% NaCl, 0.01 M Na2PO4, 0.01% sodium azide, 0.05%
Tween-20; pH 7.2). Similarly, 200 μl aliquots of Yucatan plasma
samples were added to PABET buffer and the volume balanced
to 300 μl per tube; samples were assayed in triplicate. Immedi-
ately thereafter, the samples were incubated in rabbit anti-ovine
leptin primary antiserum (1:30,000) (Dr. D. H. Keisler, University of Missouri, Columbia, Mo.) for 24 h at 4°C. The samples then
were incubated with 100 μl of 125I-labeled ovine leptin (25,000
counts/min) for 20 h at 4°C. The reactions then were incubated
for 15 min at 22°C with a pre-precipitated sheep anti-rabbit
secondary antiserum (Dr. D. H. Keisler, University of Missouri,
Columbia, Mo.) and antibody–antigen complexes precipitated
by centrifugation at 3000 ×g for 30 min. The supernatant was removed, and the radioactivity in the pellets was counted for 1 min
on a LKB1275 gamma counter (LKB Wallac; Turku, Finland).
Surgical euthanasia. Swine were euthanized in accordance
with guidelines from the American Veterinary Medical Association Panel on Euthanasia (1). After the experimental procedures,
which were performed in swine under isoflurane anesthesia, a
scalpel was used to cut through the skin and expose the chest
cavity. A rib spreader was used to provide access to the heart. A
clamp was placed on the aorta, and then the aorta was severed.
The heart then was removed from the animal and used in other
experiments (not described in this paper).
Analytical chemistry assessment of body composition.
After surgical euthanasia, the viscera were removed from the
remainder of the carcass and kept separate throughout the subsequent processing of the tissue. The visceral component of the
pig consisted of all of the internal organs, including loose adipose
tissue, found within the abdominal cavity. Subcutaneous abdominal fat was not included in the visceral fraction.
The carcass of each animal was cut into sections by using a
band saw and then stored at –20°C for 1 to 5 months. These
frozen sections were coarsely ground in a large industrial meat
grinder (25 HP, 155 rpm, ratio 11.39 from an electric Lincoln motor [Lincoln Motors, Cleveland, Ohio] with a Falk motorreducer
[Falk Corp., Milwaukee, Wis.]) using a 6.2-ml die. The resulting
mixture was ground twice more to ensure an even mixture of
contents. The coarse mixture was ground to a fine powder using a
Hobart industrial grade mixer–processor (two cutting blades, 12
HP, 3500 rpm, with a top stirrer). Dry ice (3.6 to 4.5 kg) per sample was added to ensure that the sample remained frozen without added moisture. Each sample–dry ice mixture was ground for
approximately 6 min. A final sample (250 to 350 g) was removed
and stored at –20°C. The visceral fraction from each animal was
prepared in the Hobart mixer as described, without the course
grinding, for separate chemical analysis.
Quantitative proximate analysis was performed by the Experiment Station Chemical Laboratories at the University of Missouri
(Columbia, Mo.) according to standard Association of Analytical Chemists (AOAC) procedures (15). Briefly, crude fat was determined from 2.0-g samples by using the gravimetric method
(AOAC 954.02) with acid hydrolysis preceding ether extraction.
Crude protein was determined from 1.0-g samples using the copper catalyst Kjeldahl procedure (AOAC 984.13). Crude ash was
determined from 2.0-g samples (AOAC 942.05). The moisture content was determined from 2.0-g freeze-dried samples by vacuum
drying in an oven at 95 to 100°C (AOAC 934.01).
Statistical analysis. The results of the anthropometric and
chemical body composition analysis are presented as mean ±
standard error. One-way analysis of variance was performed,
and multiple comparisons were made using Bonferroni’s post-hoc
analysis. Correlations between the analytical chemistry composition analysis and the circumference, ultrasound, and serum
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Table 1. In vivo characteristics of the porcine model
Experimental groups
Weeks 0 to 19
Percent change in body weight (%)
Control
Hyperlipidemic
Diabetic
dyslipidemic
Diabetic dyslipidemic
+ exercise-trained
Statistics (P < 0.05)
20 ± 1
59 ± 2
60 ± 4
57 ± 4
C < H, DD, DDX
Week 20
Body weight (kg)
59.9 ± 1.1
79.6 ± 3.1
69.3 ± 3.5
72.7 ± 3.2
C < H, DDX
Week 16-17
Fasting blood glucose (mg/dl)
66.0 ± 7.3
74.1 ± 5.6
323.6 ± 22.0
357.5 ± 13.8
C, H < DD, DDX
Week 20
Total fasting plasma cholesterol (mg/dl)
54.7 ± 3.9
299.9 ± 38.6
405.5 ± 74.2
354.0 ± 62.2
C < H, DD, DDX
Week 20
Total fasting plasma triglycerides (mg/dl)
27.2 ± 3.4
33.9 ± 3.8
61.7 ± 12.0
59.6 ± 17.7
No differences
Week 16
Resting heart rate (beats/min)
59.4 ± 3.1
71.1 ± 4.0
75.3 ± 3.8
59.0 ± 2.3
C, DDX < DD
C, control; H, hyperlipidemic; DD, diabetic dyslipidemic; DDX, diabetic dyslipidemic plus exercise-trained.
Data are presented as the mean ± standard error.
Statistical significance was determined by one-way analysis of variance and Bonferroni post-hoc analysis.
leptin values were determined using Pearson’s product-moment
coefficient of correlation. Simple regression analyses were performed to determine statistical significance of the correlations.
Statistical significance was defined as P < 0.05. Statistical analyses were performed using SigmaStat and SPSS software (Systat
Software Inc., Richmond, Calif.).
Results
In vivo indicators of hyperlipidemia and diabetic dyslipidemia in the porcine model. The in vivo indicators of hyperlipidemia, diabetic dyslipidemia, and exercise training are
summarized in Table 1. The percentage change in body weight
from week 0 to week 19 was significantly (P < 0.05) increased
in the hyperlipidemic, diabetic dyslipidemic, and diabetic dyslipidemic plus exercise-trained swine above control values. This
finding was expected because all animals fed the high-fat, highcholesterol diet were maintained at a 3% weight gain/week by
using feed and insulin algorithms (3). Fasting blood glucose
levels were elevated approximately fivefold in the diabetic dyslipidemic and diabetic dyslipidemic plus exercise-trained animals, indicative of alloxan-induced hyperglycemia. Total fasting
plasma cholesterol levels were elevated approximately five- to
sevenfold in all animals fed the high-fat, high-cholesterol diet.
There was no significance difference in total fasting triglyceride levels between groups. The efficacy of the treadmill exercise
was indicated by the decreased resting heart rate in the diabetic
dyslipidemic plus exercise-trained animals compared with the
diabetic dyslipidemic animals. Other indices of training efficacy
have been published elsewhere (3, 22, 23).
Non-invasive measurements: body circumference and
ultrasonography. Anatomical circumference and ultrasound
measurements were obtained to assess validity of noninvasive
measures to estimate body fat in male, Yucatan miniature swine
(Table 2). There were no differences in the neck circumference
between groups. Both the mid-abdomen and widest-abdominal
girth circumference measurements were significantly (P < 0.05)
greater in hyperlipidemic swine than control animals.
A ‘proof of concept’ experiment was performed to demonstrate
that the ultrasound images that were obtained in the live animals coincided with our visual assessment of subcutaneous fat
448
ex vivo. The group data clearly indicated no difference between
ex vivo fat thickness and ultrasound measures, and the r2 values
were reasonable: 0.25 for ventral neck and 0.46 for mid-abdomen. Ultrasound neck measurements demonstrated a significant
(P < 0.05) increase with hyperlipidemia from control. Ultrasound
measurements demonstrated a significant (P < 0.05) increase in
mid-abdominal subcutaneous fat in the hyperlipidemic swine,
and exercise training attenuated the increase seen in the diabetic dyslipidemic animals.
Serum leptin levels. Hyperlipidemic and diabetic dyslipidemic swine groups that exhibited increased body fat also showed
significantly (P < 0.05) elevated serum leptin levels compared
to control swine (Table 2). This increase in leptin was not simply the result of high fat, high cholesterol feeding, because in
our previous studies, pigs that were fed a similar composition of
high fat, high cholesterol feed (except sucrose), but in which kcal
consumed (and thus body weight) were matched to those of pigs
on the control chow diet (3, 14, 25, 34), did not show increased
leptin levels compared with those of control-diet pigs. Taken together with the positive correlations of body weight and leptin
with percentage body fat in the present study, it seems that body
weight (body fat), not the fat and cholesterol composition of the
diet, correlates with leptin increases in male Yucatan swine. Exercise training attenuated the diabetic dyslipidemia-induced
rise in serum leptin levels compared with those of the diabetic
dyslipidemic swine.
Direct chemical composition analysis. Proximate chemical composition analysis is the most accurate method for assessing body composition. In these studies we performed individual
chemical composition analysis on the carcass and visceral components to assess body fat composition accurately in the each of
these compartments separately. Table 2 contains the summary
data for the proximate chemical composition analysis. Carcass
and visceral fat were significantly (P < 0.05) elevated in the diabetic dyslipidemic swine compared with control values. The lack
of statistical difference for the exercise-trained versus control
and diabetic dyslipidemic values indicates that exercise training
attenuated, but did not completely prevent, the increase in body
fat percentage.
Linear regression analyses. Linear regression analyses
Body fat in Yucatan swine
Table 2. Circumference, ultrasound, analytical chemistry composition, and serum leptin analyses
Experimental groups
Control
Hyperlipidemic
Diabetic
dyslipidemic
Diabetic dyslipidemic
+ exercise-trained
Statistics (P < 0.05)
Circumference measurement (cm)
Neck
Mid-abdomen
Widest girth
71.7 ± 1.6
92.1 ± 1.4
92.5 ± 1.3
73.8 ± 5.7
102.6 ± 1.9
102.7 ± 1.9
74.1 ± 1.5
98.5 ± 2.1
98.7 ± 2.0
76.0 ± 1.1
99.9 ± 2.3
100.7 ± 2.5
No differences
C<H
C < H, DDX
Ultrasound measurement (mm)
Neck
Mid-abdomen
7.2 ± 0.8
9.9 ± 1.0
12.2 ± 1.3
14.5 ± 0.9
11.1 ± 1.5
12.2 ± 0.9
9.7 ± 1.3
10.3 ± 0.6
C<H
C, DDX < H
Serum leptin levels (ng/ml)
2.0 ± 0.1
4.6 ± 0.5
4.3 ± 0.3
3.4 ± 0.5
C < H, DD
Analytical chemistry analysis (% of sample)
Carcass fat
Visceral fat
16.7 ± 1.4
14.5 ± 1.9
22.7 ± 1.3
26.3 ± 1.8
23.9 ± 2.0
23.6 ± 2.1
21.4 ± 1.9
20.6 ± 2.3
C < DD
C < H, DD
C, control; H, hyperlipidemic; DD, diabetic dyslipidemic; DDX, diabetic dyslipidemic plus exercise-trained.
Data are presented as mean ± standard error.
Statistical significance was determined by one-way analysis of variance and Bonferroni post-hoc analysis.
were performed to assess the predictive power of the circumference, ultrasound, and serum leptin values in the estimation of
body fat in the Yucatan swine. Table 3 contains the results of the
regression analyses between noninvasive measurements and
carcass fat, whereas Table 4 contains the results of the regression analyses between noninvasive measurements and viscera
fat. Although each of the noninvasive measures was significantly
(P < 0.05) correlated with the amount of fat in the carcass sample, the strength of the association was indicated by the r2 value.
Widest abdominal girth circumference and neck ultrasound
measurements had the strongest predictive value (r2 = 0.440)
in the estimation of carcass fat. Similar to regression analyses
with the carcass fat, all of the noninvasive measurements were
significantly (P < 0.05) correlated with the amount of visceral
fat. For visceral fat, the noninvasive measure with the strongest
predictive value (r2 = 0.508) was the mid-abdominal circumference measurement. Importantly, the direct chemical composition analysis of the carcass fat component was significantly (P
< 0.0001) and strongly (r2 = 0.720) correlated with the amount
of visceral fat.
Using the linear regression analyses and the noninvasive
measures with the strongest predictive value, we developed two
linear regression equations that can be used for the estimation of
carcass fat in adult (ages, 8 to 15 months), male Yucatan swine.
These equations are provided below as equations 1 and 2.
Carcass Fat (%) = (0.562 × [Widest Girth Circumference (mm)])
– 34.42
(1)
Carcass Fat (%) = (0.949 × [Neck Ultrasound (mm)]) + 10.868
(2)
Discussion
The results from the current study validate the use of noninvasive body circumference and ultrasound measures for the
estimation of body (carcass) fat in adult (ages, 8 to 15 months),
male Yucatan swine. This finding is very important because although the validity of noninvasive measures has been clearly
established for commercial swine (31), predictions of body fat
from noninvasive measures are not the same for miniature feral
swine (32). Weingand and colleagues (35) used ultrasonography
and computerized tomography to predict total intra-abdominal
adipose weight in miniature swine. We have extended their findings by correlating indirect measures with direct chemical composition measures of separate viscera and carcass compartments
and the effect of exercise training on these compartments.
In the present study, the combination of alloxan-induced diabetes with the high-fat, high-cholesterol diet induced approximately five-fold increases in fasting blood glucose levels and
approximately six-fold increases in total fasting plasma cholesterol levels, consistent with previous reports from our lab (3, 7,
25, 33). Hyperlipidemia and the addition of chronic hyperglycemia resulted in increases in both the carcass and visceral fat
components. Thus, there appears to be no preferential deposition
of fat into intra-abdominal stores.
Exercise training is a well-established treatment for effective weight loss by way of reducing body fat (6, 13, 18). The exercise-trained animals in the present study had reductions in
both carcass and viscera fat, however neither of these reductions was statistically less than those for the diabetic dyslipidemic group, indicating that exercise training attenuated, but
did not completely prevent, the increase in body fat percentage.
The intentional maintenance of the diabetic dyslipidemic plus
exercise-trained swine on a 3% body weight gain per week by
increasing their food allotment precluded the typical reduction in
body weight in trained pigs that would naturally have occurred
throughout the training period compared to the maintained body
weight of sedentary pigs during the same period. The benefit of
this experimental design was that it allowed for direct examination of the effects of exercise without the confounding results of
differences in body weight.
While it was of great interest to include female Yucatan swine
in this study, the increased complexity of the experimental design and cost were prohibitive. Indeed, gender effects in diabetes
are of great interest in the field, because over a 10-year period
there has been a 2% increase in the prevalence of the metabolic
syndrome in men compared with a 24% increase in women (9)
and a 13% decrease in heart disease mortality in diabetic men
compared with a distressing 23% increase in diabetic women
(12). Our study of Ossabaw female swine (8) showed a markedly greater propensity to obesity and the metabolic syndrome
than noted for Yucatan males in the current study; therefore,
future work is needed to evaluate the separate effects of breed
and gender.
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Table 3. Linear regression analyses for non-invasive measures versus
percentage carcass fat
Percentage carcass fat (%) versus
Body weight
P
< 0.01
Y-intercept
Slope
r2
2.340
0.267
0.308
Table 4. Linear regression analyses for non-invasive measures versus
percentage visceral fat
Percentage visceral fat (%) versus
P
Y-intercept
Slope
r2
Body weight
< 0.0001
–10.933
0.459
0.489
0.299
0.430
0.440
Circumference measurements
Neck
Mid-abdomen
Widest girth
< 0.01
< 0.0001
< 0.0001
–46.961
–57.476
–57.140
0.908
0.802
0.796
0.326
0.508
0.503
0.949
0.792
0.440
0.195
1.630
0.623
0.187
0.720
Ultrasound measurements
Neck
Mid-abdomen
< 0.01
< 0.001
8.942
3.405
1.196
1.548
0.382
0.422
Serum leptin levels
< 0.01
11.330
2.739
0.310
Circumference measurements
Neck
Mid-abdomen
Widest girth
< 0.01
< 0.001
< 0.001
–28.840
–33.765
–34.420
0.663
0.557
0.562
Ultrasound measurement
Neck
Mid-abdomen
< 0.01
< 0.05
10.868
11.941
Serum leptin levels
Percentage visceral fat
< 0.05
< 0.0001
15.236
7.860
Statistical significance was defined as P < 0.05.
Statistical significance was defined as P < 0.05.
Although all of the noninvasive circumference and ultrasound
measures were significantly (P < 0.05) correlated with the analytical chemistry composition assessment of carcass fat, we found
that the values with the strongest predictive power (r2 = 0.440)
were the widest girth circumference and neck ultrasound measurements. Similar to their correlation with carcass fat, all of the
noninvasive measures were significantly (P < 0.05) correlated
with the analytical chemistry composition assessment of visceral fat. The measure with the strongest predictive power (r2
= 0.508) was the mid-abdominal circumference measurement.
Pintauro and colleagues (29) identified excellent correlation between dual-energy X-ray absorptiometry and chemical analysis
in pigs whose percentage body fat ranged from 10 to 32%, which
is precisely the range in our study. Therefore, it appears that
in both the Pintauro study and our present work, the range of
values was satisfactory for a valid test of the predictive power of
the indirect methods.
Although the abdominal girth circumference measurement
and the neck ultrasound measurement exhibited an equal ability to estimate carcass fat in the Yucatan swine, the use of circumference measurements has several distinct advantages over
the ultrasound technique. These include the minimal cost in
purchasing a tape measure, the ability to readily repeat measurements, and the ability to perform measurements in living,
conscious animals. The disadvantage in using this technique is
that observer error can affect the ability to make repeated, accurate measurements if anatomical landmarks are not used. This
limitation is not a factor when using ultrasonography.
One striking finding from our study was the strong predictive
power of the direct chemical composition analysis of visceral fat
to estimate carcass fat in the same animals (r2 = 0.720). This
analysis was not a noninvasive measure, but given the relatively
large size (~70 kg) of the swine, this tight correlation could allow
for future estimates of carcass fat without the need for laborious
whole-carcass grinding and analysis.
Multiple regression analysis demonstrated that no combination of these variables would provide better estimates of carcass
or visceral fat than any single variable. However, it is possible
that other variables that were not obtained in this study could
enable us to develop a multiple regression equation that may
increase our predictive power. This aspect will explored in future
studies in our lab.
The adipose-derived cytokine leptin has been shown to significantly correlate with subcutaneous fat thickness in humans (21),
ruminants (5), and swine (2). In the Yucatan miniature pig, the
data presented here demonstrated a robust, 2.2-fold increase in
serum leptin in sedentary obese groups and attenuation by exercise training. The significant positive correlation between serum
leptin levels and both carcass (r2 = 0.187) and intra-abdominal
fat (r2 = 0.310) might suggest that leptin could be used as a simple, noninvasive, and quantitative predictor of percentage body
fat. Our data indicate, however, that widest girth (r2 = 0.44), not
leptin, is the method of choice because leptin has lower predictive value and is more invasive (requires venipuncture) than is
a simple tape measure. However, our leptin results demonstrate
clearly that Yucatan miniature swine and lean humans respond
to dietary interventions similarly and further emphasize the
benefits of this porcine model in the study of human metabolic
diseases and health.
In conclusion, the results of our present study demonstrate
that single anatomical circumference measurements, as well as
single ultrasound measurements, are valid estimates of body fat
percentage in adult male, Yucatan swine.
450
Acknowledgments
This work was supported by National Institutes of Health grants
RR13223 and HL62552 to Michael Sturek. We thank James P. Vuchetich
for his artistic rendering of the pig.
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