2004 Poultry Science Association, Inc.
Antibodies: Alternatives to Antibiotics
in Improving Growth
and Feed Efficiency
M. E. Cook1
Animal Sciences Department, University of Wisconsin, Madison, Wisconsin 53706
Primary Audience: Nutritionist, Researchers, Allied Industry
SUMMARY
The consolidation of poultry since the 1950s largely depended upon two primary management
tools: vaccination and antibiotics. These two tools allowed for the prevention of both bacterial and
viral infections that could greatly impact poultry raised in large numbers. Antibiotics were also
found to improve poultry growth and feed efficiency over 10% when fed below therapeutic levels.
Hence, by the late 1950s, the use of antibiotics for improving growth and feed efficiency in
consolidated poultry flocks was commonplace. Early in the discovery of antibiotics, the development
of resistance was always a concern, particularly in humans’ consuming animal products that were
fed antibiotics. While science never conclusively supported this concern, advocate groups persuaded
users of poultry products to avoid foods derived from animals fed antibiotics. Scientists studied
the theories supporting the mechanism(s) by which antibiotics improve growth. Products to improve
animal performance in the absence of antibiotics have included: enzymes, competitive microbial
species, precolonization of the gastrointestinal tract with favorable microbial species, and dietary
additives that inhibit microbial attachment to the intestinal mucosa. A recent addition to dietary
substances that improve growth and feed efficiency in poultry and other species are egg antibodies
that specifically target processes involved in the immune regulation of growth. Antibodies to
neuropeptides and the rate-limiting enzyme, phospholipase A2, in eicosanoid synthesis are presented,
along with the hypothesized mechanism of action. Evidence suggested that egg antibodies offer a
new strategy in improving the efficiency of animal performance.
Key words: antibiotic, growth,
anticholecystokinin, neuropeptide
feed
efficiency,
egg
antibody,
antiphospholipase
A2,
2004 J. Appl. Poult. Res. 13:106–119
INTRODUCTION
The ecosystem of the poultry house is a rich
study of the interface among the vertebrate, the
microbe, and the overwhelming environmental
conditions that govern animal and microbial interplay. The intense interaction between the
kingdoms Animalia and Monera in the confines
of the poultry house, or any other intensively
raised agriculturally relevant species, provides
1
a unique opportunity to explore human intervention in the natural relationships and dynamics
of diverse living organisms. The ecosystem of
the poultry house and modern management of
it offer scientists a unique setting to discover
developmental strategies of species living in
confined cohabitation.
The gastrointestinal tract of the avian, or for
that matter any animal species regardless of the
environment and imposed managerial practices,
To whom correspondence should be addressed: [email protected].
COOK: INFORMAL NUTRITION SYMPOSIUM
represents the stage upon which the animal must
cope, benefit, and defend against its microbial
neighbor. Estimates have been made that the
bacterial component to the weight of an animal,
particularly in the gastrointestinal tract, is 1 to
2% of the animal’s weight [1, 2]. The symbiotic
role between this microbial mass and the fowl
has an evolutionary function that can not be
denied, but in the intensive environment in
which poultry are raised today, in light of human
intervention, one should question its value in
modern agriculture.
The discovery and use of antibiotics and vaccination in animal agriculture have evolved from
the management of small poultry flocks in the
era prior to1890s [3] to the large consolidated
units of today [4]. The current state of antimicrobial use in animal agriculture suggests that “continual and fearless sifting and winnowing by
which alone the truth can be found” [5] must be
renewed by scientists studying the ecosystem of
the poultry house.
ORIGINS OF ANTIBIOTICS
IN ANIMAL HUSBANDRY
The topic of microbial resistance to antibiotics began soon after their discovery and before
their commercial use. Scientists have always
challenged the commercial use of antibiotics in
animal agriculture. While the debates have raged
over the quality of the science supporting or
banning the growth-promoting use of antibiotics
in animal husbandry, recent history suggests that
the arguments for or against an antibiotic ban
are academic. If resistant microbial populations
are the outcome of antibiotic use in poultry, the
industry will stop using them due to fundamental
economics. If the consumer is willing to pay for
any added cost of antibiotic-free animal products, whether based on science or the result of
advocacy, the industry will supply antibioticfree products. Numerous papers have been published on the value of antibiotics to society and
implications of their use in animal feeds. Historical justification for the use of antibiotic in animal
feeds [6] and evidence for an antibiotic ban in
animal feeds continues to be based on poor science. We have moved beyond an era that scientific justification is accepted as a sole reason for
using a given practice. To the marketer of a
poultry product, science lags far behind social
107
opinion, market force, purchase power, and consumer use in the decision process.
No greater triumphs in modern medicine
have occurred than the discovery of vaccination
and antibiotics. Vaccination allowed us to move
beyond the scourge of viral infections, and antibiotics treat the bacterial diseases. With these 2
modern technological advances implemented in
modern animal agriculture, the industry
changed, and great efficiency in food production
was realized.
President Herbert Hoover’s prediction of “a
chicken in every pot, and a car in every garage”
[7] preempted the use of antibiotics in consolidating the poultry industry (the stock market
crash of 1929 and the beginning of the depression occurred shortly after his platform), and
hence prosperity fulfilled his prediction. Perhaps, the discovery of antibiotics was as critical
to prosperity as was the war.
As with antibiotics and so many other scientific discoveries, a typical period between discovery and commercial use is over a decade.
Ernest Duchesne (1896, Germany) was the first
to provide evidence of an antibacterial substance. However, its rediscovery was not again
recognized until Flemming (1928, England),
after a weekend vacation, noted that a mold on
his agar plates had lytic activity to his Staphylococcus cultures. Penicillium mold was cultured,
but the antimicrobial compound was not fully
isolated. It was not until 1941 (Florey, Chain,
Fletcher, Gardner, Heatly, and Jennings) that the
potential use of the antimicrobial from Penicillium cultures was first realized [8]. Welch and
Marti-Ibanez [8] described the first positive response to penicillin in a terminal patient in London. While the use of penicillin in this human
experiment demonstrated many signs of improvement resulting from staphylococcal infection, the patient later died when the experimenters ran out of the crude extract [8, 9].
The microbial discoveries in the world continued to reveal new compounds to treat and
prevent bacterial infections. Selman Waksman
in 1943 [8, 10] discovered streptomycin and its
use for treating tuberculosis. His patents went
on to be considered among the top 10 patents
that influenced the world. In 1945, Waksman
coined the term “antibiotic” [8].
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The implementation of antibiotics in treating
human infectious bacterial diseases was rapidly
followed by the treatment of animal diseases.
Moore et al. in 1946 [11] showed that streptomycin improved growth in chicks. The growth promoting value of this work was overlooked.
Meanwhile, T. Jukes joined Lederle Laboratories (NY) in 1942. In his studies involving
fermentation methods to make vitamin B12, a
cofermentative factor, chlorotetracycline (trade
name, Aureomycin), was discovered [12]. This
discovery, along with previous research on vaccination, provided the final pieces to allow the
rapid consolidation of poultry industries and the
realization of Hoover’s 1928 presidential platform [13].
As early as 1945, Flemming and others reported that microbial resistance to antibiotics
was a serious concern with regard to their use.
Within 10 yr of antibiotic use in humans, resistance to penicillin was reported to exceed over
50% of hospital patients [9].
MECHANISMS
OF ANTIBIOTIC ACTION
Antibiotic use in animal feeds and as antimicrobial therapy for disease continued to grow
beginning in 1951 [14]. Dafwang reported that
the total antibiotic use in animal feeds approached 50% of the total amount synthesized
in 1978 [15]. These numbers appear to be in
contrast to the Animal Health Institute [16],
which suggested that the level of use may be
lower. Witte [17] reported that in Denmark in
1994, only 0.1% of vancomycin entering the
country was used for humans, and the remainder
was used for animal agriculture. In Australia, 2
antibiotics with a similar mode of action, vancomycin and avoparcin, when combined, 99% of
the antibiotics was used for animal feeds, and 1%
was designated for human therapy [17]. Hence,
much confusion remains in published statistics
on the actual use of antibiotics for human and
animal purposes. However, the animal use of
antibiotics appears to be a significant part of
the market.
As the use of antibiotics in animal feeds
increased soon after their discovery, scientists
soon attempted to explain the mechanism by
which antibiotics enhanced growth. Postulated
mechanisms for improved animal performance,
in the absence of overt infectious bacterial diseases, were numerous [6, 14]. Antibiotics were
shown very early to have no growth-enhancing
effects in the absence of normal microbial intestinal flora. In a study by Levs and Forbes [18],
dietary antibiotics offered no growth-promoting
activity in germ-free conditions. The exposure
of chicks to bacteria decreased body weight by
11% when compared with chicks raised in a
germ-free environment. Improved growth in the
presence of bacteria was 7%, if antibiotics were
also fed. Clearly the value of improved growth
resulting from feeding antibiotics was evident
from these early studies. Strategies were identified early and repeated later that would improve
animal performance in the absence of antibiotics. Roura et al. [19] showed that increased sanitation of broiler facilities could offset the benefit
of using dietary antibiotics to improve animal
growth and feed efficiency. Increasing the floor
space given per broiler by more than 2.5-fold
was also shown to eliminate the benefits of using
dietary antibiotics [20].
Doubling the infrastructure to raise the modern day broiler or attempting to mimic a disinfected environment were not feasible management techniques in improving the animal’s efficiency to a level observed with dietary
antibiotics. Also at risk of not realizing the efficiencies achieved with antibiotics was maintaining a global advantage in the meat food market place and the cost of animal products. In
addition to the above cost, increased use of natural resources, labor cost, and environmental concerns would limit the use of sanitation and increased floor space to maintain productivity
without the use of antibiotics.
A clear understanding of how sanitation and
decreased density improved animal growth without the use of antibiotics has been discussed in
detail. Readers should refer to previous publications [4, 21, 22, 23, 24, 25]. Underlying mechanism of how antibiotics, sanitation, and density
affect animal growth, and the physiological and
immunological mechanisms have been explained previously [26, 27].
ANTIBIOTIC RESISTANCE
Resistance of microbes to antibiotics was
well recognized soon after they were discovered
(see above). The debate over the human health
COOK: INFORMAL NUTRITION SYMPOSIUM
hazard involving the use of antibiotics in animal
feeds for the purpose of improving animal performance rages on and is nothing new. Neither
side of the argument for or against the use of
antibiotics to improve animal efficiency has provided a strong enough argument to settle the
debate. Clearly, if the use of antibiotics were
such a problem in animal feeds, as has been
described by the proponents for the “ban of their
use, humankind would be today as susceptible
as the London police officer when infected with
Staphylococcus in 1941 [8]. Instead of arguing
about the issue of resistance, perhaps we should
accept it.
Witte [17] described the use of antibiotics
in a longitudinal study in eastern Germany that
best exemplifies the role of antibiotics in human
risk. In a small community, noureseothricin was
introduced to improve pig performance in 1983.
Prior to its introduction, no resistant bacteria
were found to noureseothricin. The antibiotic
was fed to improve swine growth from 1983 to
1990. During this period, the microorganisms in
the animals and the people of the community
were monitored for resistance to the antibiotic.
Also during this period, nouresothricin was not
used in human therapy.
By 1985, resistant Escherichia coli was
found in the intestine and meat of the antibiotic
fed pigs. In 1987, resistance to noureseothricin
was found in the human pathogen, Shigella (not
a swine pathogen). Escherichia coli resistance
to the antibiotic was found in pig farmers and
the people in the community by 1990. This type
of longitudinal study is absent from much of the
literature on both sides of the argument for or
against the use of antibiotics in animal production. Instead, trace-back and epidemiological
studies [28, 29] have played a major role in
policy making in the United States with regard
to antimicrobial use. These studies [28, 29] have
probably served best as teaching documents on
the discernment of scientific literature rather
than as documents for policy making.
The lack of solid science showing a relationship between feeding antibiotics to animals and
bacterial resistance in humans is not due to the
lack of talent of scientists around the world, but
the short sightedness of funding for the types of
projects needed to support such science. Over
50 yr have passed, and the answer is as clear as it
109
was in 1945, with the overwhelming observation
that people are not succumbing to the same bacterial infections prior to antibiotic use in animal
agriculture, as our most compelling evidence.
Long-term, longitudinal research investments,
such as 10 to 20 yr of study, are needed to
determine the real effects of animal antibiotic
feeding on human health.
The current issue on the use of antibiotics
in animal feeds is no longer centered on the
science of whether or not antibiotics use in animal feeds is a harm to humans, the issue is the
market. A chicken is in every pot, and 2 or 3
cars are in every garage. The public is well fed,
and now they are looking beyond food, shelter,
and water, and basic needs. As scientists, we
know better than to ignore the basic needs of
mankind. Scientists see beyond the enterprise
of human want and desire. When properly
funded, the science will be available when society’s wants become needs again.
Antibiotics use in animal feeds originated
from a need to efficiently feed humankind. However, when the needs of humans for low-cost,
abundant, and nutritious foods were met, advocacy groups demanded that food companies be
“committed to social responsibility” second to
“emerging science” [30]. Hence, the needs of
the people were replaced by social wants and
not by science. The consequence of a ban on
the use of antibiotics for improving animal performance when based on social appeal rather
than science can best be studied from the Danish
antibiotic ban [31].
The early decision on the use of antibiotics
in animal feeds is worthy of classical systems
thinking [32]. While the benefits were “a chicken
in every pot and a car in every garage,” every
change in a management strategy has unintended
consequences (see the pheasant example under
Consolidation in page 98 of Cook, 2000 [4]).
Unintended consequences of feeding antibiotics
to animals as well as their removal as a management strategy should now be given careful
thought. Table 1 shows the consequences of a
ban or continued use of antibiotics for improved
animal production efficiency. What remains
clear, however, is “industrial investment in alternatives to antimicrobials for animal growth promotion should...[protect] the fragile resources
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TABLE 1. Unintended consequences of the prohibition
or continued use of antibiotics to improve growth and
feed efficiency in farm animals
ProhibitionA
Continued useA
New drug incentiveB
Food-borne disease
Increased food price
Reduced meat consumption
Emerging pathogens
Resistance
New drug needs
Pharma health
Residues
Surface water pollution
A
Prohibition would be a ban on the use of feed antibiotics
for improving growth and feed efficiency in farm animals.
Continued use would represent use for growth and feed
efficiency as well as therapeutic uses for the treatment of
disease.
B
New drug incentives would represent a loss of incentive
for the development of new drugs for human and animal
use, hence, decreased “Pharma” (pharmaceutical industries)
to maintain markets for product development.
that are critical to successful management of
human infectious disease” [17].
ALTERNATIVES TO ANTIBIOTICS
FOR IMPROVED
ANIMAL GROWTH
As previously mentioned, scientists do not
focus on the wants of the populous but their
needs. In fact, in the area of biological science,
we have no skills in meeting wants of people.
However, we are faced with the balance between
the consumer of the product with which our
science focuses and with the needs of production
to meet both needs and wants, knowing all the
while in today’s surplus, wants far exceed needs.
Consumers will not pay more for chicken
meat unless packed in a manner that is to their
advantage. Consumers will not pay for health,
environment, conservation, welfare, food safety,
or any other advocate agenda item. Consumers
may expect these items, but only a very small
fraction will pay for them. Science must develop
food-related technologies that improve human
health and safety, promotes conservation, and
environmental sustainability.
In animal agriculture, novel methods to improve efficiency of meat production must be
developed if antibiotic use decreases. Hence, any
improvements, which will serve as a replacement for antibiotics in animal feed, must enhance growth, improve feed efficiency, or decrease mortality at no additional cost to the
consumer.
A number of strategies have been developed
to improve animal productivity beyond the traditional nutrient formulation. All of these strategies seek to use natural methods to obtain results
achieved by the feeding of antibiotics based
upon some fundamental mechanism of antibiotics. There is no question that dietary enzymes
have become a very useful product in animal
diets. Depending on the nature of the basal ingredients in a diet, responses achieved with dietary
enzymes can be quite dramatic. Increased use
of enzymes in animal feeds will continue as
efficiency becomes more essential in animal production. Several microbial intervention technologies have been developed in an attempt to
replace 1 microbial species with another. While
the principle of this technology is based on a
recognized theory of exclusion, broad use of this
technology has not been widespread in the US
meat animal industries. Continued definition of
uses and limitations and improved technologies
for producing cost-effective products still offer
promise for these products. With some of these
products, there is also preliminary data that suggest improved animal and human health. The
latter is unlikely to justify their use in animal
feeds. Nutritional strategies to provide nutrients
for growth of favorable microflora have also
been proposed. More recently, natural substances, which prevent the adherence of select
microflora (microbial adherence inhibitors),
have been reported as a method of improving
animal production efficiency [33]. Clearly, the
scientific community and allied industries have
invested significantly in the discovery of alternatives to antibiotics. These technologies will require repeated experimentation and testing by
poultry and swine users as these technologies
improve.
Antibodies
Beginning in the early 1980s, we became
interested in the use of antibodies as a means of
enhancing growth. At the time, the only largescale means for antibody production appeared
to be egg yolk antibodies. Historically, nonfood
uses of eggs were based upon physical and nutritive value. Most of these nonfood uses were
largely replaced with new technologies, such as
adhesives, media, shampoo, and purified proteins. This latter use, purified proteins, suggested
COOK: INFORMAL NUTRITION SYMPOSIUM
TABLE 2. Quantity and value of select proteins in 1
egg that have been used by research scientistA
Protein
Ovoinhibitor
Ovalbumin
Avidin
Lysozyme
Antibody
QuantityB
(g)
0.06
2.20
0.002
0.135
0.015
111
TABLE 3. Potential US needs for eggs containing an
antigen-specific antibodyA
Gross value
per eggB
($)
300
1,540
10
34
150
A
The gross value of the selected purified proteins from eggs
is approximately US$2,034.
B
Quanity of the protein is the amount of protein found in a
50-g portion of edible egg. Gross value of egg is the current
market value of that quantity of purified protein (Sigma
Chemical Company, St. Louis, MO).
that the egg had tremendous value. Using a
Sigma Chemical catalog (St. Louis, MO), we
calculated the value of a select group of pure
proteins found in an egg (Table 2).
For a laboratory setting, the egg is a rich
source of high-value proteins that have specific
and unique biological functions. Attempts have
been successfully made on the commercial use
of select egg proteins. For example, avidin, due
to its affinity for binding biotin, is commonly
used in immunological-based bioassays. Lysozyme now sells for approximately US$150/kg.
When added at a level of 0.3 g/liter to white or
red wine, microbial stability is improved, and a
reduction in the amount of sulfite, as a stabilizer,
is needed [34].
The commercial use of lysozyme represents
an example of added value to an egg, even
though the market value of the product, when
sold in mass quantities, is much less than shown
in Table 2. However, the fraction of select egg
proteins for purposes other than their current
intended use as a food, could greatly improve
the value of an egg product.
Egg antibodies are also a valued egg protein
for both laboratory and commercial use. The
ability to change the binding specificity of an
antibody by a mere vaccination procedure provides an unlimited array of antibodies with capacity to recognize virtually any epitope. Commercial companies and animal units on campuses currently provide egg antibody synthesis
for laboratory needs (see [35] for an example).
All universities that maintain a flock of laying
hens should offer, for a fee, this service for their
User
Quantity
of eggs
needed
per year
Hens
needed
People
Farm animals (1 product)
Manufacture (1 use)
92 billion
8 billion
7 billion
340 million
29 million
25 million
A
The assumptions made consider the use of one egg per day
per person of a specialized egg product in the United States.
Hens needed: assume that 270 eggs per hen would be
produced. Estimates for farm animals and manufacture are
arbitrary units only to illustrate the potential demand for an
antibody with a valued end result.
scientists as an alternative method for generating
antigen-specific antibodies.
The question we proposed in the early 1980s,
while providing this service at the University of
Wisconsin-Madison, was if 45 tons of antigenspecific antibody could be generated per year
for a commercial use, what antigen would it be
targeted toward? In Table 3, we estimated the
market potential for an egg antibody of high
demand for an end use. One potential high value
use of eggs as a source of antibodies could increase the demands for laying hens in the United
States by 10 to 100%.
Egg Antibodies to Improve Growth and
Feed Efficiency in Animals. Beginning in the
mid 1980s, our work initially focused on the
generation of egg antibodies in the breeding hen
that could be passively transferred to the progeny, by way of the yolk, to enhance progeny
productivity. Passively transferred antibody to
urease was found to enhance progeny growth
and feed efficiency [36, 37]. This work was
based on the studies of Visek at the University
of Illinois, who had demonstrated that ammonia
production in the gastrointestinal tract limited
animal performance [38]. While this work appeared promising, other targets were soon identified.
Studies involving passively transferred antibodies were stopped early in our work since the
technique required handling individual breeders
throughout their reproductive life for repeated
injections. Methods to control the titer of passively transferred antibody and the short duration of their effects (first 3 wk of life) limited
the value of this approach. Hence, the objective
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TABLE 4. Effect of feeding egg yolk antibodies to CCK on broiler chick performanceA,B
Yolk typeC
DoseD
(g/kg)
3-wk weight
(g)
3-wk
consumption (g)
3-wk
conversionE
Control
Control
Immune
Immune
0.125
0.25
0.125
0.25
558
541
561
588
909
887
875
888
1.63
1.64
1.56
1.51a
a
Different from the respective control (P< 0.05).
Unpublished data.
B
This trial represent 1 of more than 30 trials testing the effects of egg antibody made to cholecystokinin (CCK). Typical
trials consist of 5 pens of 5 broiler chicks per treatment in battery brooders with raised wire floors.
C
Control = eggs from hens injected with adjuvant and carrier protein not containing conjugated CCK. Immune eggs = eggs
from hens injected with adjuvant plus the carrier protein conjugated to CCK.
D
Dose = grams of dried egg yolk of product used per kilogram feed.
E
Feed consumed divided by body weight.
A
was to develop an egg antibody that could be
fed to animals that could enhance the efficiency
of meat animal production. The second major
objective was to obtain patents to improve the
likelihood of commercialization. While discussed in more detail elsewhere [39, 40, 41, 42]
antibodies directed to prevent immune-induced
wasting were selected as the targeted mechanism
[19, 26, 27].
Antineuropeptide Antibodies. Klasing et al.
had shown that the growth suppression and anorexia of immune stimulation were the direct
result of the release of select cytokines, such as
Interleukin-1 (IL-1) [43]. They also showed that
when IL-1 was directly incubated with skeletal
muscle, decreased muscle synthesis and inTABLE 5. Effect of feeding egg yolk antibody to
neuropeptide Y on chick growth and feed efficiencyA,B
Trial
Trial 1
Trial 2
Trial 3
Trial 4
Mean
A
Weight
gain
over
controlC
−1%
+13%
+8%
+17%
+9%
Feed
conversion
over
controlC
12
5
13
2
8
points
points
points
points
points
Unpublished data.
Experimental design is similar to that described in Table
4.
C
Weight gain over control is the percent-improved body
weight gain (0 to 3 wk) of chicks fed dried egg yolk powder
from hens vaccinated with neuropeptide Y conjugated to
bovine gamma globulin. Control fed chicks had no antibody
to neuropeptide Y. Points of feed conversion = hundredths
of kilograms of less feed per kilogram gain when compared
with control-fed chicks.
B
creased muscle degradation was induced. Similar results were also reported in other research
involving mammals [44, 45, 46]. Egg antibodies
are not absorbed when supplemented in the diet;
hence, target epitopes for preventing the decline
of performance associated with conventional
housing [18] had to be associated with an epitope
that was luminally exposed in the intestine. Two
works suggested that IL-1 was involved in the
anorexia associated with immune stress [47, 48].
These works suggested that IL-1 was responsible
for the release of a neuropeptide, cholecystokinin (CCK), which in turn decreased appetite during immune stimulation. Rao [49] had shown
that neuropeptides are released into the intestinal
lumen. Hence, it was hypothesized that animals
fed antibody to the CCK peptide would have
increased growth due to enhanced appetite (Figure 1). During an immune challenge, the macrophage would release IL-1, which was essential
for the proliferation of antigen specific immune
reactive cells. Interleukin-1 would also direct
systemic physiological changes, such as muscle
wasting [22, 26, 27, 43] and anorexia due to
the release of neuropeptides [47, 48]. Fed egg
antibodies to these neuropeptides (i.e., CCK)
would bind the neuropeptides in the intestinal
lumen and thereby improve animal performance.
Antibodies to numerous neuropeptides were
made and fed to broiler chicks to assess growth
rates and feed efficiency under conventional environments. Antibodies to both CCK (Table 4)
and neuropeptide Y (aneuropeptide Y; Table 5)
improved broiler chick performance. The basic
mechanism of this improved performance was
never determined but seemed to be unrelated to
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FIGURE 1. Proposed mechanism by which immune challenge increases muscle wasting and induces interleukin1-induced anorexia.
the regulation of feed intake [41, 42]. Commercialization of the antineuropeptide technology is
currently being accomplished by Arkion Life
Sciences, LLC (formally, DCV Biologics) [50].
Antiphospholipase A2 Antibodies. In studies
unrelated to the egg antibody technology, we
were actively studying immune-induced growth
depression caused by IL-1 and tumor necrosis
factor. These investigations [4, 21, 22, 23, 24,
25] suggested that the regulation of eicosanoid
production was a mechanism to prevent immune-induced decreased performance. While
initial work focused on the systemic regulation
of growth depression caused by immune challenge, another antigen for targeted antibody synthesis became evident.
A physiological effect of feeding antibiotics
is decreased intestinal weight and thickness [14].
Increased thickness or weight of the intestine in
conventionally raised chickens when compared
with those raised in germ-free conditions could
largely be attributed to accumulated immune defenses directed toward intestinal bacteria in the
lumen of the intestine (Figure 2). The cost of
maintaining this intestinal immune surveillance
was hypothesized to be decreased rates of gain
and feed efficiency. A reduction of immune
stimulating intestinal microflora by using dietary
antibiotics, increased sanitation, or reduced flock
density (above) would, in turn, reduce the immune challenge between the gastrointestinal microflora and the mucosal barrier (hence, the intestinal immune defense). This would, in turn,
result in decreased intestinal thickness and improved growth and feed efficiency that approached conditions realized in germ-free environments (Figure 3).
If the ecosystem of the broiler house were
stable, generation after generation of genetic selection of animals for performance in immunestimulating environments would be governed by
the model presented in Figure 3. However, not
only are the microbes changing in the ecosystem
of the broiler house, particularly due to management strategies that improve animal growth and
feed efficiency, but also the animal is changing
with each subsequent generation [4]. We hypothesized that genetic selection for growth and
feed efficiency was also having a negative impact on immune performance. Using an elite
line of duck grandparents, we investigated the
relationship between body weight and cell-medi-
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FIGURE 2. The condition of the gastrointestinal tract of animals in a conventional environment. Output = the
response of a conventional environment as compared with a germ-free environment.
FIGURE 3. Proposed mechanism by which antibiotics stimulate animal performance. In the absence of gastrointestinal bacteria due to the feeding of antibiotics, the need to recruit immune cells to the intestine is reduced; hence,
animal performance (output) is improved.
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FIGURE 4. The correlation between body weight and cell-mediated immunity index (CMI) in an elite line of breeding
ducks undergoing selection for improved body weight gain (unpublished data). A grandparent population, used
for selection, were bled, and lymphocyte blastogensis to concavalin A was assessed. The correlation, −0.38 was
significant (P < 0.05).
ated immunity (measured by mitogen-induced
blastogensis). Ducks with the greatest body
weight in a given population and generation had
the poorest relative cell-mediated immunity
(Figure 4). These results suggested that improved animal performance could be achieved
by either decreasing the amount of immune stimulation (i.e., sanitation, decreased density, or by
TABLE 6. Effects of feeding egg antibody to
phospholipase A2 (PLA2) on chick growth and feed
efficiencyA,B
Weight
gain
over
control
Trial
Trial
Trial
Trial
Trial
Trial
A
1
2
3
4
5
+6.0%
+6.4%
+7.3%
+3.6%
+3.7%
Feed
conversion
over
control
4
9
8
6
4
points
points
points
points
points
Unpublished data.
See Table 5. Mean improvement in gain = 5.4% and points
of improved feed conversion = 6.2 points.
B
use of dietary antibiotics) or by immune suppression (decreased inflammation; Figure 5).
Studies involving conjugated linoleic acid
(CLA) had suggested that one of the mechanisms
by which CLA had so many biological effects
on animal health was through the eicosanoid
pathway [24, 25]. Hence regulation of the eicosanoid pathway at an intestinal level was hypothesized as a mechanism to reduce immune-induced gut wall thickening (inflammation) and
thereby enhance animal performance. Eicosanoids can be proinflammatory and were believed
to be involved in the animal’s response to a
conventional environment. The precursor for eicosanoid production is arachidonic acid in the
sn-2 position of phospholipids in the cell membrane. Upon response to certain stimuli, phospholipase A2 (PLA2) cleaves arachidonic acid
from the phospholipids where it is converted to
prostaglandins or leukotrienes by action of the
cyclooxygenase or lipoxygenase pathways. In
turn, the released eicosanoids can recruit inflammatory cells to the site of their release
116
JAPR: Symposium
FIGURE 5. A proposed model of the reason selection for increased growth rates in immune-stimulating environments
causes reduced immunological function (or inflammation). Enhanced growth in a conventional microbial environment
can be realized by the suppression of immune or inflammatory function of the animal.
(hence, gut wall thickening). Microbes have also
evolved to release their own forms of PLA2.
Microbial PLA2 was believed to be a mechanism
by which microbes gain access into the animal
(invasive factor). Hence, it was hypothesized
(Figure 6) that egg antibody directed toward
PLA2 would improve animal growth and feed
efficiency when the antibody was fed to conventionally housed animals [51, 52]. This technology is currently being developed by August LLC
in Madison, Wisconsin.
Antibody was made to a variety of PLA2
sources in laying hens. Eggs were collected,
dried, and fed to broiler chicks in a series of 3wk battery trials. Table 6 summarizes the results
of improved performance when chicks were fed
antibody to PLA2.
Antibacterial Antibodies. A number of other
strategies to use egg antibodies to improve animal growth and development have been developed. GHEN Corporation [53] and Nutreco [54]
have developed egg antibody products that specifically target select microorganisms in the gut
mucosa. These products are designed to improve
overall gut health which in turn improves animal
growth and feed efficiency.
WHY EGG ANTIBODIES?
Hein [55] provides an excellent review on
the use and need for antibodies in human therapy. Their preferred method of antibody synthesis for pharmaceuticals is by the use of
transgenic plants. While this technology will be
cost effective for monoclonal antibodies for human systemic use, it is unlikely to compete with
the laying hen for products mentioned above.
The hen offers many advantages for the production of antibodies. The polyclonal nature of the
antibody allows one to rapidly proceed in developing an effective antibody for a use without
defining the epitope of importance. Gene arrangement identification, insertion, and cloning
would be necessary for antibody synthesis using
crops or fermentation. Hence the time, labor,
and input cost to realize an effective product
is much more rapid using the laying hen. The
technical skill and infrastructure to produce egg
antibodies already exist. The only limitation is
COOK: INFORMAL NUTRITION SYMPOSIUM
117
FIGURE 6. Proposed mechanism by which dietary egg yolk antibody to phospholipase A2 (aPLA2) improves animal
growth and feed efficiency. Dietary aPLA2 binds both microbial (mPLA2) and mucosal cellular (cPLA2) PLA2,
preventing the cleavage of arachidonic acid from the sn-2 position of mucosal phospholipids, whereupon it can
be enzymatically converted to inflammatory eicosanoids.
to identify the targeted antigen and demonstrate
efficacy. Regulatory issues favor the use of egg
antibody technology. Antibodies are naturally
found in many of the animal foods that we currently eat, if not destroyed by food processing.
In addition, humans and animals have a long
history of antibody exposure whether orally or in
systemic circulation. On a cost-per-unit efficacy
basis, egg antibody will likely remain competitive with antibodies derived from transgenic
sources.
CONCLUSIONS AND APPLICATIONS
1. Universities who maintain a laying flock should consider providing other investigators on their
campus with an egg antibody synthesis facility.
2. Antibodies targeted toward specific epitopes that may be related to human and animal disease
should be developed and tested using egg yolk antibodies.
3. Alternative methods to improve animal growth, with and without growth-promoting antibiotics,
should be tested.
4. Commercial testing and improvements of existing egg antibody products should be considered.
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Acknowledgments
Milt Sunde of the University of Wisconsin provided the freedom
and encouragement that allowed the author to pursue this research
interest for the last 21 yr. Many graduate students worked with the
author over the years developing some of these concepts. Their names
can be found in the list of publications and patents in the reference
section. Mingder Yang has also greatly assisted in more recent development in egg antibody technology and provided great technical
assistance in the development of this manuscript. S&R Farms has
generously supplied pullets and laying hens over many years. For
many years Maple Leaf Farms has opened its door to staff and
materials to explore concepts presented in this paper. Wisconsin
Alumni Research Foundation has provided fundamental intellectual
protection for additional investment in egg antibody commercialization.