POULTRY GUT DEVELOPMENT AND ITS COMPONENTS
Feed is the prime entity in poultry industry which exposes the bird’s gastrointestinal system to various factors affecting its microbiome and immunity. During the development of poultry gastrointestinal system, embryonic small intestinal weight increases at a much greater rate than bodyweight during the process of incubation.During the last 3 h of incubation, the ratio of small intestinal weight to body weight increases from approximately 1% on hour 17 of incubation to 3.5% at hatch (Uni et al., 2003, Yegani and Krover, 2008).
The small intestine continues to increase in weight more rapidly than the rest ofbody mass in the post hatch period. Increases in intestinal weight and length are not equal or similar in the duodenum, jejunum, and ileum. Intestinal development after hatch is also rapid with respect to enzymatic and absorptive activities(Uni et al., 1999; Sklan, 2001; Yegani and Krover, 2008). During the initial 48 h post hatch, yolk contributes to small intestinal maintenance and development (Noy and Sklan,1999).When access to feed is delayed, birds show slower intestinal development and depressed performance (Potturi et al., 2005).
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The structural category of avian immune system is mainly represented by the lymphoid organs. The bursa of Fabricius (a site of Blymphocyte development and differentiation) and the thymus (which is the site of T-lymphocyte development and differentiation) are primary lymphoidorgans (Qureshi et. al., 1998).In chickens, the Gut Associated Lymphoid Tissue (GALT) includes the primary lymphoid components of bursa of Fabricius, cecal tonsils, Peyer’s patches, and lymphoid aggregates in the urodeum and proctodeum constitute the secondary lymphoid components (Befus et al., 1980).
The microflora of gastrointestinal tract is composed of bacteria, fungi, and protozoa, but bacteria are the predominant microorganisms (Gabriel et al., 2006).Ithas been shown that the composition of the microflora changes in relation to the age of the chickens, dietary factors, breed, and geographic location (Lu et al., 2003).
Learn MoreBroiler chicken feed ration containingcorn, sorghum, barley, oats, or rye impose increased numbers of Enterococcus, barley-based diet increases numbers of Lactobacillus, oats-based diet enhances the growth ofEscherichia and Lactococcus, and rye-based diet increases the number of Streptococcus in broiler chickens(Apajalahti, 2004).
FACTORS AFFECTING GUT HEALTH IN POULTRY
Gut health in poultry is decided by multitude of factors of which the most important are as follows:
Feed (dietary regime) and water quality
Though a variety of feed ingredients are available for poultry, the most prevalent anti- nutritional compound present is the non-starch polysaccharides (NSP) which tend to create a viscous environment within theintestinal lumen leading to digestive and health problems by means of decreased passage rate of digesta and nutrient availability. This further leads to bacterial colonization and activity in the small intestine. In addition to that, the physicalform of cereal components of feedmay affect the morphological and physiological characteristics of the intestinal tract. Finely groundfeed has the tendency to increase mortality associated with necrotic enteritis when compared with coarsely ground feed. (Yegani and Krover, 2008).Steps should be taken to minimize grain damage and conditions that could increase mold or insect spoilage.
Acceptable water qualityis also important for proper digestion. Hence, its physicochemical characteristics should be measured, controlledand improved at the farm level. pH of the water should be maintained slightly acidicbetween 5.5 and 7, because basic water reduces theactivity of most digestive enzymes. Water deprivation or feed withdrawal can cause gut mucosa traits shift making chickens more susceptible tomucoid enteritis (Oviedo-Rondon, 2019).
Digestibility and gut-microbiome host equilibrium
When intestinal health is discussed, it is usuallyfocused on the control of intestinal disease. Usually, the focus tends to be placed on coccidia or specific enterobacteria like Clostridium perfringens, E. coli, or Salmonella spp. This misinterpretation comes from day-to- day experience in which the above said are the main health issues observed when a problem with intestinal health is detected.
The true problem is an excess of nutrients in the hindgut which causes the proliferation of these microbes in thehindgut (Chan et al., 2013) leading to disruption of gut microbiome- host equilibrium causing the metabolic, pathogenic or sterile inflammation.Excessive nutrients in the hindgut may either be due to high nutrient levels in the diet or suboptimal digestion (Brown et al., 2012).
Infectious diseases
Low level damage to the GI tract by the pathogenic bacteria might lead to poor feed conversion efficiency and decreased body weightgain in poultry flocks.The lesions of necrotic enteritis (NE) could be the most severe of any disease that occurs in the chicken intestine. As far as parasites are concerned, protozoal organisms are most common. When the chickens are reared in confinementand flocks of high density have increased exposure to parasitic diseases such as coccidiosis that have short and direct life cycles (no intermediate host is needed). Also, many viral infections are associated with enteric disease conditions.This includes rotaviruses, coronaviruses, enteroviruses,adenoviruses, astrovirusesand reoviruses.Feedborne toxins can cause enteric disease.The mycotoxins and biogenic amines are the most common examples of feed borne toxins.Diagnosis of the presence of mycotoxins in poultry feed has been a widespread cause of economic loss causing impaired health status and reduced performance (Yegani and Korver, 2008).
Environment and housing
With broilers, layers, environmental stressors like heat/cold, very dry or veryhumid air could alter their feed intake patterns and intestinal motilitythereby causing reduced digestion and the ensuing gutproblems.
All environmentalstresses highly affect the immunological system of broilers, which disables them from maintaining microbes insidetheir GIT lumen and translocation of bacteria to the bloodstream can occur (Oviedo-Rondon, 2019).Birds tend to become highly susceptible to necrotic enteritis when the stocking density is higher.
Apt and proper ventilation of the poultry house is key forintestinal health to minimize condensation, litter moisture, and caking (Dunlop et al., 2016). The litter moisture should be kept below 30% but it is also important that litter does not become too dry (Oviedo-Rondon, 2019).
Poultry gut health estimation and its recent interventions
It’s a well-known fact that a healthy gastrointestinal system can help poultry achieve optimal production of meat or eggs. Intestinal bacteria plays a key role in health through theireffects on gut morphology, nutrition, pathogenesis of the intestinal disease and immune responses.
There are several products available to support gut health which can either be added to water, added to the feed at the feed mill or top dressed on feed at the farm level.Antibiotic Growth Promoters (AGPs) have been used worldwide in poultry feed for several years together. AGPs improve feed conversion and growth, and reduce disease incidences due to Clostridium perfringens. However, concerns about the use of AGPs have been raised by the scientific community and consumers are on the rise of which the most important is development of antimicrobial resistance in animals.Commonly available alternatives to antibiotics are probiotics (live microbial feed supplements), prebiotics (indigestible diet component causing through selective stimulation of growth and/or metabolic action of useful bacteria already present in the intestine and suppressing pathogenic bacteria), enzymes, biosurfactant, mycotoxin binder, organic acids (lactic, acetic, tannic acid etc.), essential oils and bacteriophages. An ideal combination of two or more of the abovealternativesmight be capable of performing well or on par with AGPs.
In the yester years, the knowledge of intestinal microbial community (MC) of poultry had beenlimited to information obtainable from culturedependent techniques, which are prone to selectivity bias due to the nature of the isolation media used.Also, culture-basedtechniques have limited options which can detect only readily cultivated bacteria, numbers of which remainlow due to lack of knowledge of nutritional requirements and stress imposed on bacteria bythese techniques. These limitations have been overcome throughdevelopment of sophisticated nonculturedependent, molecular technology suitable forMC analysis (Roberts et al., 2015).
The development of new technologiesaid in differential diagnosis of emerging enteric health issues of poultry flocks. They are based on the direct extraction of bacterial DNA from intestinal samples and subsequent sequencing of thetaxonomically relevant genes. With the help of this method, many more bacteria in the chicken gastrointestinal tract than had been previouslyidentified through culture-dependent methods have been differentiated (Apajalhti, 2005; Roberts et al., 2015).
These new technologies include:
PCR assays, Denaturing Gradient Gel Electrophoresis (DGGE), temperature gradient gel electrophoresis, terminal-restriction fragment length polymorphism, microarrays, next- generation sequencing, ultra-pressure liquid chromatography, mass spectrometry, metagenomic sequencing, meta-metabolomics, and FLX-titanium amplicon pyrosequencing (Kohl, 2012; Roberts et al., 2015).
The benefit of microbial technologies includesbeing able to: enhance our understanding ofcomposition and function of intestinal microbiota, identify shifts in MC by rapidly identifying and enumerating the presence of a widerange of microorganisms, enhance understanding of relationships which exist between hostsand microbiota and help to advance theselection of alternative products which promoteintestinal health (Stanley et al., 212; Roberts et al., 2015).
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Conclusion
In poultry production, intestinal health is of supreme importance for performance and productivity. Poultry gut health can be improved by efficient feed composition, medication and additives to maintain a rich and diverse microbial community, and control of host reaction through dietary immunomodulation.Housing and management, water quality and on top of all biosecurity at all the levels are highly important.Precision in feed formulation and phase feeding is also needed.The technologies which have been developed recently for poultry industry provide further understanding and differential diagnosis of emerging microbial ecology issues. These technologies have paved a way to a far more complex chicken intestinal microbiome than once believed.
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