Using the Feed to promote Gut Health, By OLUYINKA A. OLUKOSI PhD Assistant Professor Department of Poultry Science University of Georgia

775

Feed is a major component of the intricate chain of interrelated factors that make for a successful poultry production. Poor feed management will compromise nutrient digestion and absorption which will ultimately lead to inefficient feed conversion and poor productivity. The term “gut health” has become somewhat a household vocabulary both in human and animal nutrition arenas. Gut health involves complex interaction among factors such as nutrient digestion and absorption, digestive epithelial cells integrity, gut microflora flux, and mucosal immune response, among others.

It is no surprise that feed is a major factor in ensuring optimum gut health because it passes through the digestive tract (gut); and the gut is an entryway which various nutrients and metabolites can start their systemic access. The digestive tract, with its layer of epithelial cells has digestive, immunological, absorptive and metabolic functions, among others. Therefore, disruption of the wellbeing of the digestive tract will have negative consequences on a wide array of body systems. The overt negative effects on animal production resulting from intestinal disorders associated with consumption of harmful substances (e.g. toxins) are well known. However, subtler negative effects from feed mismanagement might not be immediately apparent but may add up to produce compromised productivity. Consequently, using the feed to ensure a robust gut health is critical to ensuring optimum performance and reduction of ill health. In that respect, the feed can be seen as an ally from a familiar place; and hence it is important to consider aspects of feed quality with potential contribution to improving the gut health.

The ultimate goal of feed processing and other nutritional interventions (for example the use of additives) is to help optimize digestibility. The economic importance of improved digestibility is immediately obvious as it ensures that the nutrients in the feed are not wasted but are used by the animal. However, there are more advantages that may be less obvious, but not without significant benefit to overall gut health and improved feed efficiency. It is recognized that it is virtually impossible to come by any feedstuff of practical relevance that is 100% digestible. Some indigestible nutrients inevitably make their way to the hindgut where they are utilized by resident microorganisms. However, suboptimal nutrient digestibility, disease or other feed-related factors can lead to harmful accumulation of undigested nutrients in the hindgut. On one hand, some nutrients are needed in the hindgut to promote proper fermentation and reasonable level of proliferation of gut microbiota; but on the other hand, accumulation of large quantities of indigestible nutrient in the hindgut is harmful to the wellbeing of the host animal. Therefore, it is essential to ensure feed and nutrition practices that shift the balance of digestibility to the small intestine where majority of digestion and absorption of nutrients take place.

An aid to improving digestibility is paying due attention to feed particles size, especially ensuring that feed particle size is such that stimulates gizzard action. Fine grinding of feedstuffs helps increase the surface area of a feedstuff that is exposed to digestive enzymes, and hence on the surface is beneficial to optimizing digestibility. However, it has long been recognized that chickens, in their natural environment, do consume feedstuffs with various degrees of fineness, including larger particles which obviously serve important functions. For example, examination of the content of gizzard and small intestine of free range village chickens reveals the presence, among other things of nutritive values, of a significant quantity of stones and pebbles of different sizes. Such large particles are particularly located in the gizzard and clearly help with the grinding action of that organ. Several structured studies have shown that addition of coarse particles (e.g. whole grains or fiber) in the diet help to improve digestibility and development of the gizzard. Some of these effects were due to enhanced reverse peristalsis that helps improve efficiency of digestion. Although pelleting helps to even out particle size, it appears that some effects of inclusion of larger particle feedstuffs is still retained, even after pelleting. Reduced digesta pH, associated with feed with larger particle sizes, is one way of promoting gut health because such low pH is inhibitory to the development of pathogenic organisms. Consequently, paying attention to feed particle size can help reduce aberrant accumulation of undigested nutrients in the hindgut and help promote gut health.

Another potential help is appropriate use of digestive enzymes. Exogenous enzymes aid in shifting nutrient digestion to the foregut and thus reduce quantity of undigested material in the hindgut. A wide variety of exogenous enzymes are used in the industry to promote nutrient digestion and reduce nutrient excretion to the environment. Earlier studies with enzymes capable of hydrolyzing non-starch polysaccharides demonstrated positive effects with viscous feedstuffs because the enzymes helped with reducing digestive viscosity and its many negative effects on gut microbiota. More recent studies have suggested additional benefits from exogenous enzymes including a more complete destruction of phytate and possible prebiotic effects, in the hindgut, of smaller carbohydrate oligomers resulting from hydrolysis of non-starch polysaccharides. Although there are opinions suggesting that the quantities of such prebiotic effect is marginal, the likelihood exist that they may prime the development of beneficial microbiota, and in addition are used for production of short chain fatty acids. However, irrespective of how marginal such benefits of enzymes beyond nutrient digestibility effects might be, the large body of evidence demonstrating positive effect of exogenous enzymes indicate that they are allies in promoting good gut health. They do this by enhancing digestion in the foregut, which is the primary reason for their use, and hence reduce accumulation of undigested nutrients in the hindgut. Effective application of exogenous enzymes, informed by both the needs of the animal and thorough knowledge of nutritive values of feedstuffs in question, will help enhance the positive contribution of enzymes to gut health.

Another aspect of use of feed to promote gut health is processing of feedstuffs. Some processing techniques are designed to destroy antinutritive substances whereas others are intended to promote digestibility by partially destroying the more recalcitrant matrices in which nutrients may be ensconced. With specific reference to soybean meal for example, optimum processing of the feedstuff is critical to digestibility of its protein. Under-processing (with regards to heat application) of soybean produces meals with high level of trypsin inhibitors, whereas over-processing inhibits protein digestibility in all plant protein feedstuffs. At both extremes, the protein value of the meal is diminished for the animal consuming it and, worse, contributes to accumulation of excessive undigested protein in the hindgut, which is detrimental to gut health.

High level of nutrients in the diets is another possible cause of accumulation of undigested nutrient in the hindgut. Higher than necessary nutrient level in the diet may be an inadvertent consequence of excessive nutrient surfeit added as a buffer to counteract possible loss in nutrient potency during storage. Another possible cause of the problem is a mismatch between animal nutrient need and dietary supply. This may be especially relevant in the first three weeks of life of broilers, for example, when the gut microbiota is still immature and the dietary need of the bird is rapidly changing. Under conditions of excessive nutrient buildup in the hindgut, potentially pathogenic organisms that are normally non-harming symbiont, can become pathogenic. One possible way of addressing this issue is ensuring that nutrient supply is more closely tailored to dietary needs of birds. This may necessitate more feeding phases to ensure that dietary nutrient level more closely matches nutrient requirement.

In summary, efficient production is built on the foundation of effective feed and nutrient management which includes, among other things, practices that help to promote nutrient utilization in the proximal part of the digestive tract and thus reduce excessive accumulation of nutrient in the hindgut. In this way, the use of feed to promote gut health is not simply a gut feeling, but is built on solid foundation of efficient utilization of feed by the animal to enhance productivity and reduce suboptimal health.