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The following technical article is related to the event::
XVII Congress of the World Veterinary Poultry Association

Intestinal Health in Poultry

Intestinal Health and Immunity, the new challenge in poultry nutrition

Published on: 9/23/2011
Author/s : Dr. Timothy S. Cummings, DVM, MS, ACPV (Mississippi State University)
Intestinal health and immunity is the most critical system to manage in order to optimize performance in today´s commercial poultry. The development and maturation of the GI tract can be influenced by any number of factors involving genetics, nutritional, management, and health issues. The maintenance of a normal, functioning intestinal tract during grow-out is also vital to minimize the effects of enteric challenges that will occur in the field. A total program approach is required to realize a healthy GI tract which translates into better yields, feed conversion, and daily gain. 
To begin to understand how best to promote intestinal health, it´s best to be aware of the major physiological processes involved and the roles of the intestinal tract. It is one of the largest organs of the body, although many do not think of the GI tract as an "organ". Although it is understood that digestion and nutrient assimilation is the major function of the intestines, it does so via an extremely large epithelial surface area. It is the most metabolically active organ in the body with significant hormonal activity and influences. It has a very active immune system although it is loosely "organized" in only a few locations along the GI tract. Finally, it is host to billions of microorganisms in a very dynamic nature which can fluctuate greatly in numbers and types based upon any number of influences. Despite the seemingly complex nature of all these systems interacting to produce the normal intestine, there are practical management practices which can promote and maintain intestinal health.

From an applied perspective, the poultry intestines first start to develope during the egg incubation process. Nutrients for the embryo and maternal antibodies from the breeder hens can influence intestinal development and protection in the embryo, so adequate breeder nutrition and strategically designed vaccination programs play a role. Proper incubation profiles are important in optimizing hatch and chick quality, but they can also impact internal organ development. For example, abnormally high incubation temperatures have been documented to result in lower weights of the heart, liver, proventriculus, gizzard, and small intestines at hatch when compared with controls. This likely results in delayed intestinal development even if the chick looks normal. Suffice it to say that hatchery management can be a key opportunity for optimizing intestinal performance.

The first week post-hatch is critical for chick starts and intestinal performance. There are several factors which are working against the chick which need to be properly managed in order to help the bird maximize its potential. For example, the chick initially has an immature thermal regulation and will back off feed if chilled. It must transition from an "egg" to "feed" based nutrient profile all while limited digestive and absorptive capabilities. The chick also has deficient enzyme activity and an immature immune system during a period when it is struggling to establish a stable gut microflora. Fortunately, all of these areas can be influenced by management to some degree to minimize any negative effects they have on performance, but it will involve the GI tract in one way or another.
A vital aspect to manage for intestinal health is to get the chicks eating as soon as possible. It has been documented that delayed feed intake will reduce the rate of yolk utilization, suppress thyroid activity, inhibit muscle growth potential, and suppress initial immune responses. Delayed feed intake will reduce intestinal villi height and enterocyte migration rate, both of which are critical for maximizing nutrient uptake. There simply is no substitute for getting the chicks to eat immediately and often, as it will positively influence intestinal development which in turn will improve yield and performance. All management efforts during the critical, first 24 hours after placement should emphasize bird comfort and feed/water accessability in order to stimulate the chicks to eat.

One aspect of chick starter nutrition that should garner closer attention is the diet make-up of today´s poultry rations. In the U.S., poultry feeds are corn-soy based, and the day old chick is not yet capable of fully utilizing these type rations due to its immature intestines. Readily digestible ingredient alternatives should be considered in the pre-starter diets to match the chick´s intestinal capabilities. Nupro is an example of a product which makes sense in that it contains certain essential nutrients such as nucleotides, amino acids, and peptides necessary for fast growing enterocytes. Certainly there are other ingredients to be considered as well, but any increased input costs must be justified.

However, keep in mind that the best place to measure true returns is the cost per pound out of the processing plant where yield can be measured, especially on larger broilers. The process of establishing a normal microflora is also essential to maintaining intestinal health and efficiency. In earlier times, the newly hatched chick was immediately exposed to pings from the hen which contained a mature microflora from which the chick derived its normal flora over time. Today, clean eggs are set in sanitized hatcheries with resultant chicks often being placed on new litter which does not have an established microflora. Although this is not the case with built-up litter, the chick will begin the process of developing a microflora from the environment in which it finds itself. It is critical to manage this process, as the microflora make-up will have a very definite impact on intestinal health and performance. However, certain concepts need to be understood.

The microflora and micro-environment varies along the GI tract. For simplification, certain types of bacteria tend to predominate in certain regions of the intestines based largely on what type bacteria the birds are first exposed to as well as the pH, viscosity, redox potential differences, etc... which exists along the intestines. Certain intestinal bacteria are more conducive to maintaining intestinal health than others whereas some bacteria can damage the intestines under the right circumstances. The whole concept of competitive exclusion is to allow for the "good bacteria" to colonize the intestines which will exclude pathogenic bacteria from becoming attached or overgrowing the normal microflora. The earlier the chicks are exposed to "good bacteria", the earlier a stable, normal microflora will become established which then suppresses or eliminates potential pathogens. This in turn results in less intestinal damage and/or inflammation which results in better nutrient utilization. Probiotics are used for this purpose.

There a wide number of probiotics available for use by the poultry industry which are marketed to help promote a healthy microflora, but be aware that the products vary greatly as to their make-up and application routes. Follow each manufacurer´s recommendations for their specific product as there are often certain nuances associated with every product. It is best to expose the birds to the probiotics as early as possible to begin the colonization process, but also be aware that it may take up to several cycles for the full potential to be realized. Although you can influence the individual bird´s microflora rather quickly, it takes time to change the microflora in built up litter. There are varying experiences and opinions about probiotics, but also appreciate that they are simply one aspect of a total program, and their benefit may be difficult to fully appreciate if your only measurement is performance related. It seems likely that they have a definite place in intestinal microflora management, especially if Salmonella reduction is a goal as well.

Antibiotic growth promotants (AGPs) have been the backbone for intestinal health programs for decades, as they have been documented to improve feed efficiencies and rate of gain. They work in part by controlling the Clostridia spp. population in the microflora which are primary initiators of enteritis and necrotic enteritis. There have been growing concerns that antibiotic use in poultry feeds have been contributing to antibiotic resistance problems in human medicine, hence they were banned in Europe. Certain poultry meat customers and other countries have restrictions on growth promotant usage in food animal production, and it seems likely that AGPs may be further restricted at some point in the future. Other alternative nutritional ingredients such as prebiotics, enzymes, essential oils, organic acids, and herbs/spices have been used in the field as alternatives to antibiotic growth promotants.

Prebiotics such as manninoligosaccarides (MOS type products) have been increasingly used in the feed to help promote intestinal health. They work primarily by binding certain pathogenic bacteria such as E. coli and Salmonella thus preventing their attachment to the intestinal walls. One product in particular (BioMos) stands out in this category with regard to the amount of  research conducted which documents the improved performance is also due to reduced intestinal inflammation and lowered immunologic stress which ultimately results in improved nutrient absorption and a more stabile microflora. 

There does appear to be clear differences among products in this category, so price should not be the only factor to consider when considering prebiotics. Again, prebiotics should be part of a total program, albeit an important component. Use of acidifiers, organic acids, essential oils, and certain herbs/spices such as cinnamon and thyme have also been used in diets to help improve and maintain  intestinal integrity and performance in the absence of antibiotics. Again, there are several products to from with varying modes of action. They can have their place and are often synergistic with other products such as some probiotics. There have been mixed performance results in the field, but keep in mind that each complex has its own, unique grower profile, pathogen load, and other influences which could explain these variable results. 

The increased costs of grains and other feed stuffs is the major concern for poultry producers at this time, and the use of alternative grains and other ingredients has increased as a result. Enzymes should be more attractive during such times to help lower certain nutrient specs as well as improve efficient utilization of certain essential nutrients from poorly digestible ingredients. They should allow for more complete digestion of certain feed stuffs especially for young birds with immature digestive systems as previously discussed. The cost of inclusion for enzymes needs to be justified, but further evaluation on the use of enzymes is warranted, especially during periods of higher feed prices. The age old question of "can we afford to use it" may need to be replaced with "can you afford not to use it?" 
Coccidiosis control is a major factor to monitor, as it certainly can impact intestinal health and integrity. Flocks are going to be exposed to coccidia and the poultry industry has used feed additive anticoccidials or live vaccines to control this pathogen. An understanding of the typical cocci cycling patterns on the different programs is essential for assessing gut health in the field, as some degree of  enteritis (clinical or subclinical) will be associated with the peak cocci challenge period. It is critical to minimize these periods of intestinal inflammation, as it is metabolically expensive to the bird and could disrupt the stability of the microflora to the point of allowing for clinical necrotic enteritis. Immunity to coccidiosis during the starter/ grower period is the goal for most cocci control programs, as it has been recognized that even mild cocci lesions during  the withdrawal period is significantly hurting feed conversion. Finally, cocci is robbing performance to one degree or another even when it seemingly is under control, so selection of the rotational and/or shuttle cocci-control programs needs to be done with a complete understanding of the strengths and weaknesses of all the products available.

Certain mycotoxins have been clearly documented to impact numerous body systems in poultry, but the intestinal tract is certainly one of the primarily impacted organs. The degree of damage depends upon the type of mycotoxin , the level of exposure, and the length of time of exposure. Mycotoxins can decrease liver function, increase intestinal irritation, cause immunosuppression, and negatively impact a number of other functions. Most feed mills are analyzing for certain mycotoxins, but the reality is there are only tests for relatively few mycotoxins, and there are literally hundreds which likely exist. Also appreciate that feed sampling for mycotoxins have certain limitations and that mycotoxin damage is very difficult to fully assess in the field. Since alternative ingredients such as DDGs are increasingly being used in poultry diets, it could be argued that some type of mycotoxin "insurance" needs to included in the feed, especially if performance is sub-par for unknown reasons. There are several products for use in feeds but they tend to fall into one of two categories: mold inhibitors or mold adsorbants. Use mold growth in a given ingredient, but consider a mold adsorbant if you suspect mycotoxins are already present in the ingredient(s). 

Another consideration pertaining to intestinal health and efficiency is gut motility. The intestines in poultry are relatively short compared to mammals, and peristaltic refluxes are a mechanism in the bird to compensate for this short intestine. Peristalsis are muscular contractions along the GI tract which promotes mixing of the digesta with digestive secretions. This results in enhanced nutrient absorption but also discourages microbial proliferation. The gizzard is considered the pace-setter for peristalsis which is stimulated by presence of feed and large particle sizes. Thus, particle size of the feed can have an impact on gut motility and efficiency. It has been speculated that small particle size of the feed may be in part responsible for small gizzards and proventriculitis.
Lastly, a word about trace minerals and their impact on intestinal health is in order. Organic sources of these type nutrients have become available, and are more bioavailable than their inorganic counterparts. In particular, selenium appears to be especially important due to its strong antioxidant properties which impacts a host of systems. It also has been demonstrated to enhance the immune response and minimize tissue damage when various challenges occur. This is simply another option to consider when putting together a total program to optimize intestinal health and bird performance.

In closing, gut health is a complex interaction among many systems and inputs which is related not only to physical intestinal development, but is influenced by nutrition, management, genetics, and the microflora. These systems are dynamic and subtle changes can often have significant impact on gross and microscopic changes in the intestines. Having said this, there are principles that need to be considered when making certain management changes and/or decisions which will influence intestinal efficiency, and resultant performance results over time need to be interpreted accordingly. In addition, intestinal necropsy sessions and visitation to birds in the field can help assess intestinal integrity at any given point in time. Utilization of all available expertise, experience, research, and field data will help decision makers choose the best options for optimizing intestinal health.
This paper was presented at the XVII World Veterinary Poultry Association (WVPA) Congress in Cancún, Mexico, August 14-18, 2011. Engormix.com thanks the author and the organizing committee for this huge contribution. 
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