The interplay between modern management practices and the chicken: how immune response and the physiological mechanisms for growth and efficiency have adapted over time. Where do we go from here?

Although plants and animals began to be acquired as domesticants nearly 10,000 years ago, it has only been the last 50 years in which animals have been intensively raised for food. In 1892 Wehman wrote “Poultry, to be successful on a large scale must be kept in small colonies of about 50 birds, for many more than that number in a single house is apt to cause sickness or disease ere long among”. Given the scale and concentration of the modern poultry industry, one must ponder whence we have come and question how it was accomplished.

Two developments, namely vaccination and antibiotics, allowed the microbial villain of the piece to be overcome sufficiently for the movement from small animal husbandry schemes to the large scale consolidated units of today. Intensive rearing, vaccination and antibiotic use along with other more subtle changes have in the short period of animal domestication and consolidation had dramatic consequences on the nature of the bird. Contemplation of the role of management decisions on animal change is critical in determining the future and sustainability of those decisions.

In the following paper, discussion will be narrowed to one well-defined system I will call ‘the ecosystem of the chicken house’. Since this ecosystem is far more complex than can be dealt with here, the discussion will be limited to several ecological interfaces: 1) the interface of select management decisions and the chicken, 2) the interface between the chicken and its microbes, and 3) the interface between time and the chicken which reflects managementinduced genetic change. It is in this context that we begin to understand how our rearing practices, including antibiotic use, have altered the nature and physiology of the chicken. It is also in this context that we must view the value and the cost of using antimicrobials and seek new directions to maximize growth of intensively-reared birds.


Consolidation

One of the most obvious phenotypes that needed to be modified in the process of animal domestication and consolidation was behavior. The pheasant, one of the more recent wild animals in the US to be placed into domestic conditions in large scale will serve to illustrate domesticated selection. To produce a released bird, ready for hunting season and capable of building a stable flock (the long term goal) these fowl had to be brought into captivity.

However, this had unintended consequences in that captivity adjusted behavior as successive generations over time were bred in confined space. When wild pheasants were first placed into confinement, they were put into outdoor flight pens often 200-300 feet long and 50 feet wide. They were rectangular in configuration with posts holding containment wire or nylon netting. However, the posts supporting the wire or nylon netting needed interior support to prevent post collapse, especially during heavy snow and ice. Hence, the original flight pens had an obstacle to flight (the support post) that would accidentally kill the flying pheasant. The consequences of breeding 30 generations of pheasants in this consolidated environment were that birds surviving to breeding age were the least likely to fly.

When confronted by the caretaker, the most likely survivor fled on foot. Hence, over the course of many generations, game farm pheasants became runners, not fliers. Leading game breeders recognized the problem, namely that management practices had selected for a tame species. Recognition of this problem led game producers to import wild individuals from China. These were used to breed back traits lost in the more domesticated birds. However, current flight pen construction had to change. Confinement and rearing of a wild species, pheasant, serves to illustrate the consequences of consolidation and the rapid change of a species based upon a simple decision on whether the support beam is on the inside of a flight pen or on the outside.


THE ROLE OF VACCINES AND ANTIBIOTICS IN INTENSIVE REARING

The modern poultry industry has moved from 50 bird flocks to the 1 million plus flocks (layers) or 1 million processed broilers per week in a 30 mile radius of an integrated broiler unit. Vaccine and antibiotic strategies were adopted by early leaders in the poultry sector in order to consolidate animal units and to maintain a competitive edge in animal agriculture. This assured, in the case of chickens, that a valuable food (eggs and meat) would be available to the consumer at a fraction of its cost in 1900. The success of these two management strategies remain a marvel, and assured the modern Western world that food shortages would not limit human pursuits.

The entire animal food industry hinges on the discovery and production technologies of vaccination and antibiotics. Vaccination was not only one of the most brilliant discoveries of mankind, one only need examine the history of poultry science to learn the value gained from vaccination strategies to prevent disease. Once scientists realized that the microscopic world had its own weaponry, antibiotics, we began using them against microbes. This brilliant strategy in disease prevention was quickly moved to the chicken house. An added benefit appeared in that when using antibiotics in animal agriculture to fight disease, animals grew faster and used less food per unit body weight gain. The reason for this remained a mystery until the explanation was provided by Kirk Klasing of U.C. Davis (discussed later).

Vaccination and antibiotics became crucial tools in the consolidation of the poultry industry; and the interface between the chicken and the microbial world was subdued through their use. The revelation that continual feeding of antibiotics promoted growth and feed efficiency resulted in subtherapeutic use of antibiotics on a continual basis in the chicken ecosystem.

The ramifications of continual antimicrobial use for performance effects in the chicken house were far-reaching. Poultry products became affordable to all households. Soon antibiotic use in animal feeds represented 50% of antibiotics made in the US. This meant that pharmaceutical companies could finance the discovery of new human cures, partly on the back of profits realized by antibiotic use in animal agriculture. Had it not been for this link between chicken growth and the cures of human diseases, we may have never enticed pharmaceutical companies to risk investments required to generate some of these products. The cost of launching a new antibiotic for use in human medicine, from concept to product, is a staggering $350 million investment. In view of such an investment, one can begin to realize the contribution of the chicken’s growth response to financing development of antibiotics for human use. More than 7.5 billion broilers are raised a year in the US. Antibiotics have historically improved growth by 5-10%. With these numbers, the importance of the chicken in medicinal development is evident.

Consolidation was, in its own right, a pressure for change in disease patterns that all of us recognize. Once winter sets in, and people spend more time indoors, the disease of one becomes the disease of all in the household, classroom, office or movie theatre. When we brought chickens together in densities less than one square foot per bird, we created an environment in which disease could quickly spread. In the chicken house we have seen two events that were catastrophic to the poultry industry in recent history: the Newcastle disease outbreak of the early 1970s in California and the influenza outbreak in the 1980s in Lancaster, Pennsylvania. Both outbreaks, while closely contained within their respective regions, cost the consumer hundreds of millions of dollars in increased food costs. Few realize that our animal food production does not far exceed human demand. The fact is that our production, particularly for inelastic markets such as eggs, barely exceeds human needs, hence the low price. During the two historical outbreaks, prices for poultry products reached an all time high even though only a small part of the nation’s production was affected.

Consolidation of an animal species increases the likelihood of the transmission of a pathogen among individuals. If we consider the strategy of the villain, the infectious organism, consolidation is the perfect medium to achieve its goals. Keeping a flock of no more than 50 birds was a perfect strategy for prevention in the 1890s, but is not sustainable if we are to maintain a low cost food supply. Hence, the greater the consolidation, the lower the food cost, but the greater the chance of the spread of an introduced infectious pathogen. Ultimately, consolidation and low food prices have driven the need for vaccination and antibiotics.

The tool of vaccination (not to be discussed at length here) was the most important vehicle for consolidation of humans and their animals. Controlled exposure to potential insults could assure that an army of educated defenders (antibodies) were in place if the attack came. Most interesting, the agricultural community largely ignored the cost of maintaining a specifically trained militia designed for only one purpose: to destroy only one enemy and often at only one frontal attack. This cost will be explored in more detail later.


Bacteria, antimicrobials and immune response: why the chicken responds to antibiotics

Of all management strategies for consolidation, none have come under more scrutiny than the use of antimicrobials. It is interesting that we group a wide range of biologically active compounds under a single term; but however diverse their activity in controlling infectious diseases, they, like vaccines and consolidation, result in change of the chicken ecosystem. For many generations, forced change has occurred rapidly.

Despite the modern misconception that if it was not published yesterday, it is not relevant to the problems of today, many of the answers to today’s questions can only be found in works dating back decades. Lev and Forbes (1959) published a paper that is pivotal in the understanding of the ecosystem of the chicken house. They showed that chickens raised in germ free environments grew faster than those exposed to conventional bacterial flora.

More importantly, they showed that the feeding of penicillin (an antibiotic known to be a growth stimulant in poultry) had no growth promoting effects in germ free environments in contrast to potent growth stimulation in bacterially contaminated environments. The improvement in growth for germ free vs. normally-exposed birds was greater than 10%. Even more importantly, antibiotics only partially alleviated the growth suppression associated with the exposure to naturally occurring microbes. Hence, their work showed that there was room for expression.

Kirk Klasing showed that injecting the cell wall of Escherichia coli (endotoxin) into chickens caused them to grow more slowly or lose weight. Why? Because the exposure of an animal to a normal flora antigen had such a negative impact on growth. The reduction in body weight gain following endotoxin exposure was 30%. His work also showed that the type of immune stimulant was not responsible for the reduction in gain. Chicks injected with sheep red blood cells also grew 17% slower than the control birds.

While never published in a full length manuscript, a group at Mississippi State University reported that “vaccination of broilers resulted in lower final body weights, poorer feed conversion and higher 8 day and 42 day mortality. Vaccination reduced overall performance in the absence of overt disease” (Chamberlee et al., 1992). We also observed a similar effect in ducks. In a study with a commercial line of ducks, we injected either a saline control or a standard killed bacterin of Pasteurella antipestifer. The injections were given at day 12 and again 10 days later. The ducks were then raised to market age. The final carcass weight of the ducks injected with the killed bacterin was reduced by 9% and the amount of breast meat was reduced by 5.4%. These data clearly showed that there was a significant cost associated with vaccination. In addition, the decreased growth and feed efficiency observed with a diverse range of antigens suggested that the reduced performance was not antigen mediated, but perhaps related to the immune response.

During the response of the immune system to a stimulus, immune cells such as the macrophage destroy and process (degrade) the stimulant and present specific parts of the stimulant to white blood cells known as lymphocytes. There are two primary classes of lymphocytes known as T and B cells. These cells proliferate to form clones of cells specifically targeted to the antigen presented. The cloned cells have increased capacity to respond in a rapid defense if exposed to the antigen in the future. The macrophage is also responsible for producing cell signals, known as cytokines, which up-regulate the immune cells during their cloning. The cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF), are two major cytokines released from the macrophage during the immune response to an antigen. Klasing et al. (1987) went on to show that the growth depression associated with endotoxin (E. coli cell wall) injection could be produced by a direct injection of IL-1. He also showed that IL-1, when placed on cultured muscle strips, increased muscle degradation and decreased protein synthesis.

Hence, the growth depression associated with immune stimulation was the result of the release of the immune cytokines and not the direct effect of the immune stimulant. Everyone can relate to the consequence of immune stimulation. When we develop an infectious disease, we lose our appetite and we lose weight. The pathogen is not responsible for these physiological changes, it is the result of immune cytokines. The use of recombinant cytokines as immunotherapy was of great interest when first discovered. However the side effects were so severe that routine use of IL-1 and TNF was never realized in human medicine.

Those of you who are actively involved in poultry production can relate to the effects of immune stimulation. In our research involving growing broilers or turkeys, we often go into the growing facility to weigh birds. During the process of data collection, litter is stirred causing the air to be filled with dust. In this dust is fecal matter rich in killed bacterial cells and hence endotoxin. After breath-ing this dust for several hours, we all experience similar signs: loss of appetite, low grade fever and fatigue. These effects are immune related. Within the next 24 hrs, the immune system slows and the adverse effects of immune stimulation are resolved. Since it is the immune products that suppress growth, it becomes evident that immune suppression or removal of the immune stimulant should enhance growth in the absence of disease.

Both immune suppression and reduction of immune stimulants (reduced bacterial load through the use of antibiotics) represent two major management strategies used to consolidate poultry. While both management strategies have moved animal agriculture toward more efficient production of food, there is a long term cost associated with them.


THE COST OF ANTIMICROBIAL USE

If animals could be reared in the absence of immune stimulation, the added performance would be valued in the hundreds of millions of dollars in the US alone. However, it is unlikely that such a process could be economic. Improved sanitation has been shown to minimize decreases in growth associated with the immune response (Roura and Klasing, 1993). In certain species one strategy used to reduce immune stimulation is ‘all in/all out’ management. In this scenario, animals are placed in a growing setting only with others of the same age. By doing so, older animals, which often become carriers of infectious pathogens, do not expose younger animals to disease agents. The swine industry experienced major improvements in growth rates when they moved from facilities containing multi-age animals to segregated early weaning strategies where piglets were removed from the sow at an early age and reared in isolation.

Since the 1950s, another management practice used to reduce immuneinduced growth suppression involved the use of antibiotics. It was observed that feeding low levels of dietary antibiotics on a continuous basis improved growth and feed efficiency. The reason for the improved performance was that antibiotics reduced the bacterial load (immune stimulants) in the gut, decreased the level of immune stimulation, and hence prevented the catabolic nature of the immune response. By the 1970s, over 50% of all antibiotics produced in the US went into animal feeds (Von Houwelling, 1978). In some countries, antibiotic use in animal feed was more than 1000 times the use in human medicinals (Witte, 1998).

Witte (1998) reported the consequence of antimicrobial use in animal feeds. The study he reported was perhaps the best longitudinal study illustrating that using antimicrobials in animal feed confers resistance to organisms in humans. In 1983 in East Germany, pigs were tested for microbes resistant to the antibiotic nourseothricin prior to its use in swine diets. No resistance was observed. Beginning in 1983, nourseothricin was used as a growth promotant in swine diets. By 1985, microbes with resistance to the antibiotic were observed in the intestinal tract of pigs and on the processed meats.

By 1990, resistant E. coli was found in the farmers and individuals in the community. In 1987, Shigella (a human pathogen and an organism not associated with pigs) was expressing resistance to nourseothricin. It is now well recognized that antibiotic resistance can be transferred across bacterial species. This resistance can be transferred both by plasmids as well as genomically. Hence, targeting these immune stimulants as a strategy for enhancing growth rate ultimately confers resistance.

What alternatives are available to assure improved growth and feed efficiency without directing the therapy to the microbial flora, or without suppressing the inflammatory response? Dafwang et al. (1987) showed that when broilers were provided with more floor space, the depressed performance associated with consolidation was reduced. In fact, these studies showed that at only the highest densities were antibiotics effective at enhancing growth rate. While these results looked promising, the cost associated with doubling the floor space for 7.5 billion broilers would be prohibitive. Our data also showed that increasing the density of broilers resulted in a reduced size of selected lymphoid organs (Bursa of Fabricius and thymus). While antibiotics enhanced the growth rate of broiler chicks raised at high densities, the use of antibiotics was ineffective at restoring the size of the bursa and thymus associated with dense populations of broilers.

A number of antibiotics have been banned in Europe, in part because it is feared that the generation of antibiotic resistance will increase human disease with no effective therapeutic treatment. Logic would have it that similar bans should be proposed in the United States. Many have expressed concerns about the consequent effects on animal health and efficiency.

The removal of antibiotics as growth promotants could cost poultry and swine producers as much as a billion dollars. One must also consider that the poorer feed efficiency could significantly increase the demand for corn and soybean meal. In addition, animals not fed antibiotics would grow more slowly and hence would not reach their market weight until days later than those fed antibiotics. This would decrease the number of animals moving through the existing infrastructure. Unless new animal units were constructed, total animal numbers produced would decline. Even more important is the potential negative effect antibiotic removal could have on human health. The continuous use of antibiotics reduces the bacterial load on an animal and hence the final meat products. Would animal products from animals not fed antibiotics represent an even more serious food safety risk?

Another indirect means by which a ban on antibiotics could affect human health involves the pharmaceutical manufacturers. Since animal agriculture represents a source of income for antibiotic manufacturers, what will be the likely outcome if this source of income is lost? Will a company be eager to spend the $350 million needed to create a new antibiotic if it will have lost a major market which helps defray these costs? If so, then the future generation of new antimicrobials for human health could be (or is) at great risk.

As one thinks about these issues, it would appear that we have created a trap that may be difficult to avoid without a major restructuring of the animal industry and allied industries. It is clear that research is needed to clearly define the costs associated with both the use and avoidance of antibiotics in animal feeds.


Genetic selection and the microbial/immune interface

Our discussion to this point clearly shows that the interface between management strategies and the microbial world is greatly linked to the immune response of an animal, with critical points of growth and feed efficiency being the driving variables needing optimization. Most of our management strategies in consolidated animal units attempt to minimize the inflammatory process, whether intentionally or by chance. The unexpected consequence, particularly with regard to the microbial world, of antibiotics was increased resistance and hence a potential human hazard.

The microbial immune interface has another dimension worthy of discussion: the effects on genetic selection. While improved growth was achieved by reducing immune stimulation (Lev and Forbes 1957 only showed a partial restoration of growth through the use of antibiotics), genetic selection for growth rate and feed efficiency was not without its effect. As previously discussed, symptoms associated with an immune reaction include decreased body weight (or rates of weight gain) and poorer feed efficiency (or anorexia). In addition, immune stimulation can actually increase mortality. These are the very endpoints we wished to improve and the reason for our desire to reduce the level of immune stimulation using antibiotics.

However, if you were an animal geneticist selecting commercial breeding stock and looking for the birds which grow the fastest and convert feed the most efficiently, which bird would you select? Would the bird with the greater or lesser inflammatory response perform best? The birds that are selected as the superior performers in theory should have the poorest immune response. In fact, from the geneticist’s point of view, the less growth depression due to immune stimulation the better. Generation after generation of selecting animals that perform in the top 20% in the typical immune stimulating environment loaded with airborne endotoxin has resulted in an animal that is less likely to mount an inflammatory response associated with the cytokines IL-1 and TNF.

We became very interested in the effects of genetic selection on the immune response of an animal. Access to such genetic lines however proved difficult. Fortunately, a duck company, Maple Leaf Farms, was interested in this question as well. This highly vertically-integrated company had its own breeding program where performance traits were selected. While the studies conducted were not pure and ideal, we were able to gain limited insight into the influence of selection for performance on immune responses.

In our first study, we compared a T cell dependent immune response to phytohemagglutinin-P. Fortunately, the company had a line of ducks that did not have heavy selection pressures (we called this line the control). The other lines were selected for rate of gain, breast meat yield, or feed efficiency. All lines selected for performance traits had reduced immunoreactivity of 28% or more when compared to the line with less (or no) selection pressure. We expanded our test to include antibody synthesis in response to an antigenic stimulus. The antibody response was 29 to 79% less in lines selected for improved performance when compared to our control. Dr. Venelin Kounev soon joined my laboratory to try to improve our understanding of growth and immune function. Working within a given elite duck line (the great grandparent lines) he was able to show a direct inverse correlation between body weight and cell-mediated immunity (r = -0.38). This means that in this line of ducks, if the top performers were selected as grandparents for the next generation, those selected would have the poorest ability to generate an immune response to a stimulus.

Others were making similar observations. In a study by Sharaf et al. (1988), turkeys selected for enhanced egg production had decreased antibody titers in response to Newcastle Disease virus vaccination. Hence, these data suggested that genetic selection for enhanced performance (whether for growth, feed efficiency, or egg production) is associated with suppressed immunological function. Work has shown that the genetic overexpression of genes for tumor necrosis factor (TNF) greatly retards growth and thriftiness of animals. Hence, the obvious effect of selection for growth in immune stimulating environments is the selection against catabolic cytokines. However, no data are available to directly support this hypothesis.

We are actively engaged in such research but have failed to convince the scientific community of its merits. Hence, grant proposals are rejected with comments of “no need to reapply”.

It appears that not only are management practices changing to enhance animal performance, but also that the immune system of our agricultural species is being modified to improve animal growth and feed efficiency. As there are consequences associated with an attempt to modify immune stimulation, there are likewise consequences in modification of the inflammatory process and other immune reactions. One consequence involves physiological processes that cells of the immune response are involved in that have little relationship to defense. Select cells of lymphoidal origin are responsible for the maintenance of tissue structure and function. The macrophage is essential in the repair and remodeling of tissues associated with growth, development and injury. Hence, one can predict that selection against inflammatory or immune processes may lead to physiological aberrations.


Out of the trap?

Clearly, new strategies are needed to assure animal growth, to maintain an immunologically expressive animal and to reduce pressure on the microbial ecosystem. Such approaches should target neither the immune system nor the microbial flora. While these targets have rewarded us with improved animal growth and perhaps even wellbeing, these targets have limitations that can be pushed only so far. We have signs that suggest that it is time to remove pressures on the microbial flora and the animal’s immune system. What are those new targets going to look like? If we need to find alternatives for maintaining the existing level of growth in animals, how will we structure these alternatives? It is now time to explore these ideas. We are landed in a kind of trap in that our management strategies of antibiotic use may lead to resistant disease organisms and our genetic selection practices result in ‘immune suppressed’ animals. Where is the door of opportunity? We have created a system of unintended consequences that demands creative thinkers.


Alternatives

Initial work with nutrition and immunity examined pharmacological levels of certain nutrients in an effort to enhance immune function and was not promising. Working with two integrated turkey companies in the early 1990s, we reformulated the diets based on experience and literature reviewed (Cook, 1991). Both companies said the results were disastrous. It was then that I realized that there was a cost to immunological function, much as Kirk Klasing was demonstrating in his work.

Other works in the literature, although sketchy, were showing similar effects. Nockels (1979) had shown that immune enhancement of guinea pigs using vitamin E had a deleterious effect on growth rate when the pigs were infected with equine encephalomyelitis virus. Gross (1992) also showed that while high dietary levels of ascorbic acid reduced lesions associated with Mycoplasma and E. coli, chickens fed the high ascorbic acid had much poorer feed conversion.

It appeared that implementation of nutritional regimes proven to reduce pathogenesis of select infectious disease was costly. Enhanced immunoreactivity suppressed performance and hence an alternative appeared necessary in the management of performance in immunoreactive animals.


CONJUGATED LINOLEIC ACID

To understand alternative methods to prevent the immune-induced growth suppression and to find ways to improve animal performance without the aid of antibiotics, a basic understanding of immune-induced growth suppression was needed. The question that had to be answered was how do immune cytokines suppress growth? Rodemann and Goldberg (1982) had shown that muscle degradation associated with IL-1 was associated with increased production of prostaglandin E₂ (PGE₂).

They went on to show (Goldberg et al., 1984) that when PGE2 was directly applied to muscle strips, the muscle degradation was increased. Based on these works, we began a series of studies to identify dietary factors that would prevent the wasting of body weight during the immune response. A number of compounds were identified; however, they all appeared to be immunosuppressive. Our goal was to prevent the loss of body weight in the immune challenged animal without having a negative effect on immune function.

We began work with conjugated linoleic acid (CLA) when Mike Pariza, a collegue in Food Microbiology and Toxicology, proposed feeding some laying hens CLA as he had found that it had potent anticarcinogenic activity. At that time, he believed that the anticancer activity of the compound might be related to antioxidant capacity. His goal was to feed laying hens CLA so he could harvest the eggs, make mayonnaise and determine if shelf life was extended. Since one mechanism in the reduction of tumor formation involved the immune system, we began collaborative studies on CLA and immunological function.

What was most appealing about CLA with regard to the Klasing model of immune-induced growth suppression was that CLA is a fatty acid markedly similar to linoleic acid (18:2, cis 9, cis 12), which was the precursor for PGE2, the lipid mediator that caused muscle wasting. The double bond configuration of CLA (18:2) prepared in his laboratory was predominately cis 9, trans 11, or trans 10, cis 12. Even more perfect was that these fatty acids were naturally occurring (see wisc.edu/cook for more detail). As predicted, CLA prevented growth suppression resulting from immune stimulation (Cook et al., 1993; Miller et al., 1994).

Later we found that it even protected against growth suppression associated with the direct injection of TNF and wasting autoimmune disease. More exciting, CLA did not prevent immune-induced growth suppression by suppressing the immune system. In fact, it enhanced the immune response. This became our first alternative to the growth suppression caused by immune stimulation. Instead of targeting the microbial world (which would only develop resistance) or the immune system (a potentially bad idea) we targeted how nonlymphoidal tissue responded to the immune system (see US Patents: 5,430,066; 5,428,072; 5,827,885; 5,674,901 and 5,725,873).

An analogy may aid in explaining these results: If one thinks of the immune system as a military force, the immune reaction as a battle, and the animal’s nonlymphoidal tissue (such as muscle) as the nonmilitary citizen where the battle is taking place, during conflict there is always collateral damage to nontargeted sites. Our hope is to minimize this collateral damage by erecting barriers. CLA was found to be a biological barrier to the collateral damage associated with the immune response.

Another area we thought would be a beneficial control point in protecting against the collateral damage of the immune response is the intestine. Of all places in the animal’s body, the intestine hosts the greatest quantity of immune stimulants. As was previously mentioned, one of the consequences of the immune response is a reduction in feed intake. Work on our campus by Donna McCarthy (Daun and McCarthy, 1993) had shown that IL-1 induces anorexia in part by causing the release of the gut peptide, cholecystokinin (CCK). CCK in turn induces a satiety effect and alters gut motility. We reasoned that if we could interfere with the actions of CCK, then we could prevent reduced feed intake associated with the immune response.

Literature suggested that CCK was released into the lumen of the intestine. This source of CCK was targeted using antibody generated against CCK. We selected the laying hen as our source of anti-CCK production since hens can be stimulated to produce high quantities of antibodies in the egg yolk. When egg powder containing antibodies to CCK was fed to broiler chickens, growth rate and feed efficiency improved. Antibodies to other gut peptides also showed similar benefits (see US patents 5,827,517; 5,725,873 and 5,989,584). While these anti-CCK antibodies were not found to stimulate food intake, they proved very effective as growth promotants. We have continued our efforts to make antibodies to other physiological processes involved in the immune response with remarkable success.

Another area in regulating immune-induced growth suppression involved the development of a method to continuously monitor when an animal is immunologically challenged. We reasoned that if we could know rapidly and noninvasively when an animal was undergoing an immunological reaction, that animal could be treated accordingly. For example, is there a means to continuously monitor layers in a large complex (a million or more) to know if a disease is in the early stages of development? If rapid detection was possible, then these diseased animals could be removed from the flock or specifically treated. To accomplish this goal we used the natural fractionation of isotopes of carbon (US patent 5,912,178).

During enzymatic processes, enzymes discriminate against substrates containing ¹³Carbon and preferentially use substrate with ¹²Carbon. We reasoned that during the immune response, as skeletal muscle is degraded and amino acids are released, these amino acids have two pathways of metabolism. They can be reused for acute phase protein synthesis or burned to CO₂ and expired. Since the complete metabolism to CO₂ has many enzymatic steps, we predicted that the amount of ¹³C in breath would decrease during the catabolic response and indeed it does. Hence, one could envision the continuous sampling of CO₂ from ventilation exhaust for monitoring ¹²C:¹³C ratios.


Summation

New strategies for the control of the microbial/immune and immune/ nonlymphoidal interfaces are critical in discovering alternatives to antibiotics as growth promotants. These strategies must not result in resistant microbes and must enhance or maintain immune function.


References

Chamberlee, T.N., J.R. Thompson and J.P. Thaxton. 1992. Effects of day old vaccination on broiler performance. Poultry Sci. 71(Suppl. 1):144 (Abstr.).

Cook, M.E., C.C. Miller, Y. Park and M. Pariza. 1993. Immune modulating by altered nutrient metabolism: Nutritional control of immune-induced growth depression. Poultry Sci. 72:1301-1305.

Dafwang, I.I., M.E. Cook and M.L. Sunde. 1987. Interaction of dietary antibiotic supplementation and stocking density on broiler chick performance and immune response. Brit. Poultry Sci. 28:47-55.

Daun, J.M. and D.O. McCarthy. 1993. The role of cholecystokinin in interleukin-1 induced anorexia. Physiology and Behavior 54:237-241.

Goldberg, A.L., V. Baracos, Rodemann, L. Waxman and C. Dinarello. 1984. Control of protein degradation in muscles by prostaglandins, Ca++ and leukocyte pyrogen (interleukin-1). Federation Proc. 43:1301-1306.

Klasing, K.C., D.E. Laurin, P.K. Peng and D.M. Fry. 1987. Immunologically mediated growth depression in chicks: Influence of feed intake, corticosterone and interleukin-1. J. of Nutr. 117:1629-1637.

Lev, M. and M. Forbes. 1959. Growth response to dietary penicillin of germfree chicks with a defined intestinal flora. Brit. J. Nutr. 13:78-84.

Miller, C.C., Y. Park, M.W. Pariza and M.E. Cook. 1994. Feeding conjugated linoleic acid to animals partially overcomes catabolic response due to endotoxin injection. Biochem. Biophys. Res. Comm. 198:1107-1112.

Nockels, C.F. 1979. Protective effects of supplemental vitamin E against infection. Fed. Proc. 38:2134-2138.

Rodemann, H.P. and A.L. Goldberg. 1982. Arachadonic acid, prostaglandin E2 and F2 influence rates of protein turnover in skeletal and cardiac muscle. J. Biol. Chem. 257:1632-1638.

Roura, E. and K.C. Klasing. 1993. Dietary antibiotics reduce immunological stress elicited by poor sanitation or consumption of excreta in broiler chicks. J. Nutr. 122:2383-2390.

Sharaf, M.M., K.E. Nestor, Y.M. Saif, R.E. Sacco and G.B. Havenstein. 1988. Antibody response to Newcastle Disease virus and Pasteurella multocida of two strains of turkeys. Poultry Sci. 67:1372-1377.

Von Houwelling, C.D. 1978. Draft environmental impact statement. Subtherapeutic agents in animal feeds. Food and Drug Admin. Washington, D.C.

Wehman, H.J. 1892. Wehman’s Practical Poultry Book. Wehman Bros., New York, pp. 110. Quoted in: Wilson, W.O. 1974. Housing In: American Poultry History 1823-1973. American Printing and Publishing, Inc., pp. 221.

Witte, W. 1998. Medical consequences of antibiotic use in agriculture. Sci. 279:996-997.