A healthy gut is essential for the efficient conversion of feed into its basic components for optimal nutrient absorption. If gut health is compromised, digestion and nutrient absorption will be affected, and bird performance and welfare will be compromised. Maintaining gut health in poultry is essential to raising top performing birds. When properly managed, good gut health in poultry empowers birds to fight off disease.
THE GUT AND HOW IT WORKS
The intestinal tract of a bird is a specialized tube that starts at the beak and ends in the cloaca. The primary function of the gut is the conversion and digestion of food into its basic components for absorption and utilization by the bird. The gut is separated into five distinct regions; the crop, proventriculus, gizzard, small intestine (duodenum, jejunum and ileum) and large intestine (ceca, colon and rectum). Each of these regions has a specific role in the digestion process and absorption of nutrients. The feed enters the crop where it is stored for a short period of time and partially fermented by the resident bacteria. The feed then enters the proventriculus where it is mixed with acid and pepsin (an enzyme which breaks down protein) and then on to the gizzard. The gizzard acts like a grinding mill to break the feed into smaller particles, it will then release the feed into the small intestine once the feed particles are small enough. While the gizzard grinds the feed, it is mixed with the acid and enzymes secreted by the proventriculus.
This process allows for the break down of whole proteins into smaller peptides which can then be digested in the small intestine into amino acids for absorption. Within the small intestine, the carbohydrates and fats are also broken down so that they can be absorbed and used by the birds. During the normal digestion process, by the time the digesta reaches the last part of the ileum all the proteins, fats and carbohydrates should have been absorbed leaving behind the non-digestible components of the feed (e.g., cellulose, non-starch polysaccharides, etc.). This material has two fates; it is either passed out in feces or taken up by the ceca where bacteria ferment these materials to form organic acids, short chain fatty acids and vitamins which the bird can absorb for extra nutrients. At the end of digestion, chickens produce two types of droppings, a cecal and a fecal which look very different.
The community of microorganisms in the gut is referred to in many ways: friendly bacteria, gut flora, gut microbiota and gut microbiome. It is a diverse community of mainly bacteria, fungi, protozoa and viruses. While modern DNA-based technologies have given a much more accurate picture of the bacterial species present in the gut, it has become increasingly evident that a large number of bacteria in the gut are currently unknown and unclassified. Recent studies focusing on poultry have proposed that the gastrointestinal (GI) tract of a broiler chicken is colonized by an estimated 600-800 species of bacteria. The abundance and diversity of the microbiota vary along the GI tract and, predictably, the regions that have less tolerable conditions and faster passage of gut contents have lower numbers of bacteria. Even though bacteria can be found in the gut of the developing embryo, it is generally considered that the development of the adult gut microbiota predominately begins at hatching where bacteria are picked up from the environment, the feed and the people handling the chicks post-hatch. The crop is rapidly colonized within 24 hours.
After one day post-hatch, the ileum and ceca are also both dominated by bacteria. After three days, the level of bacteria in the small and large intestine increases ten-fold. The first bacteria to enter the gastrointestinal tract can be considered the pioneering bacteria as they rapidly multiply and colonize the gut environment. The composition of the pioneering bacterial community goes through a succession of changes as the gut develops and oxygen levels fall. It can take up to 3 4 weeks for the microbiota to form the climax (or adult) microbiota, but during this period, stability is seen in the gut if chicks are provided with optimal brooding conditions along with good feed and water quality.
The crop harbours a large population of lactobacilli. These bacteria partially ferment the carbohydrates in the feed and produce lactic acid which reduces the pH of the crop environment. The conditions within the proventriculus are highly acidic creating an environment which is unsuitable for most bacteria. The gizzard also has an acidic environment but has a substantial population of lactobacilli which mainly originate from the crop. The bacterial population of the small intestine is made up of main lactobacilli although enterococci, E. coli, eubacteria, clostridia, propionibacteria and fusobacteria can sometimes be found. The bacterial population of the small intestine evolves as the bird ages but will generally be stable by two weeks of age. The ceca provide a more stable environment which allows the colonization of slower growing fermentative bacteria. Early in the life of the chick, the ceca are dominated by lactobacilli, coliforms and enterococci, but by two weeks of age, the cecal environment will have started to stabilize as the adult flora begin to dominate. At this stage, the pioneering species are replaced with Bacteroides, eubacteria, bifidobacteria and clostridia.
ROLE OF THE INTESTINAL MICROBIOTA Within the GI tract, there are multiple interactions between the host (bird) cells, the intestinal environment, bacterial cells and feed components. These interactions emphasize the extremely important role of gut microbiota in the health and well-being of the host (as discussed below), although the exact way in which this is achieved is not yet fully understood.
The bacterial community of the intestinal microbiota form a protective barrier which lines the gut, preventing the growth of less favourable or pathogenic bacteria such as Salmonella, Campylobacter and Clostridium perfringens. This principle is most commonly known as competitive exclusion. Theories suggest that the commensal (or friendly) microbiota dominate attachment sites on the gut cells reducing the opportunity for attachment and colonization by pathogens. Another proposed mechanism is that the intestinal microbiota is able to secrete compounds, including volatile fatty acids, organic acids and natural antimicrobial compounds (know as bacteriocins), that either inhibit the growth of, or make the environment unsuitable for, less favorable bacteria It is thought that the commensal microbiota maintain the gut immune system in a state of ‘alert’ so that it can react quickly to pathogens. The gut microbiota is also considered to be an important factor in the development and maturation of the immune system. Animals lacking a gut microbiota have been shown to be more susceptible to disease and have poorly developed immune tissues. In addition to protection against disease and stimulation of the immune system, the intestinal microbiota can influence host growth rates by producing extra nutrients through the fermentation of the plant fibres that the birds can’t digest.
THE BALANCE OF GUT HEALTH Gut health relies on the maintenance of the delicate balance between the host, the intestinal microbiota, the intestinal environment and dietary compounds. This balance can be significantly affected by factors such as bird management, feed quality and the birds’ environment. When gut health is optimal, there is complete digestion of the feed and absorption of the nutrient components. If there is a disruption to the normal processes in the gut, incomplete digestion and absorption of nutrients can occur, leading to malabsorption and gut imbalance. If there is an imbalance in the gut environment, gut health is then at risk of being compromised which can impact the health and performance of the birds. When digestion and absorption is not optimal,
there is malabsorption of nutrients resulting in more nutrients being available to the small intestinal bacteria that can lead to an overgrowth of the bacterial population. A further consequence of malabsorption is the passing of proteins, sugars and fat into the ceca causing an overgrowth in the microbial population and a shift away from the beneficial fermentative bacteria. The balance of the microbiota in the gut can be affected by factors such as:
• poor gut development
• feed change
• feed (quality and raw materials)
• environment (temperature and ventilation)
• brooding conditions
• infections with viruses, bacteria or coccidiosis
• water quality
MANAGING GUT HEALTH WITH ANTIBIOTIC: A healthy gastrointestinal system can help poultry achieve optimal production of meat or eggs. The gastrointestinal system for chicken has two important functions: digestion & absorption and immunity. The intestinal mucosa provides an effective barrier between unfriendly luminal content and the host internal tissues. A dynamic balance between the mucus layer, epithelial cells, microbiota and immune cells in the intestine is of importance for the intestinal barrier functions.
The proper balance of intestinal microbiota is highly responsible for gut health, especially the role of commensal microbiota. Commensal microbiota helps in development of gut structure and morphology, modulate immune responses, protect from intestinal pathogens, and aid in better digestion and absorption of nutrients. It is essential to maintain healthy intestinal microflora by suppressing pathogenic bacteria and promoting beneficial bacteria. Good gut health in poultry is closely linked to the normal ecological equilibrium of the gastrointestinal microflora.
Intestinal bacteria play an important role in health through their effects on gut morphology, nutrition, the pathogenesis of the intestinal disease, and immune responses. The microbial flora is also believed to protect against colonization of the intestines by pathogens and to stimulate an immune response. Gastrointestinal microflora is comprised of three categories: lactic acid bacteria (55%), rods (44%) and pathogens (~1%)1 However, many factors can affect the composition of the avian bacterial community, such as diet, age, antibiotic administration and infection with pathogenic organisms. Changes in the composition of the animal’s microflora can have beneficial or detrimental effects on health, growth, and maturation of the animal host.
COMMON GUT HEALTH ISSUES:
• Protozoan diseases – Coccidiosis.
• Bacterial infections caused by E. coli, Salmonella, Clostridium (Necrotic Enteritis), Campylobacter jejuniand Spirochaetes result in wet litter.
• Viruses such as REO, IB, IBD, New Castle Disease virus, Adenovirus, Rotavirus, Astroviruses, Turkey Corona Viruses and Toroviruses cause diarrhoea.
• Parasites – roundworm and tapeworm infestation cause diarrhoea.
A) Feed: structure and pellet quality, palatability, formulation and content, mycotoxins
B) Management: available feed space, water space, distribution of feeders, drinkers, air quality, ventilation, litter, temperature and density.
POULTRY GUT HEALTH SOLUTIONS: There are many products available to support gut health, these products can either be added to water, added to the feed at the feed mill or top dressed on feed at the farm. Gut health additives vary in their mode of action which makes choosing the right product difficult. Some gut health products provide or stimulate beneficial bacteria, some promote the development of the gut tissues, some aid digestion and others inhibit pathogens. Consequently, when deciding which product to use, it is critical to investigate what is causing the gut health issue and ensure that any potential product has the ability to help solve the issue faced.
Antibiotic Growth Promoters (AGPs) have been used globally in poultry feed for 60 years. AGPs are known to improve feed conversion and growth, and reduce disease incidences due to Clostridium perfringens. Recently concerns about the use of AGPs have been raised by the scientific community and consumers. The scientific community is discussing the ability to develop antimicrobial resistance in animals. Consumers are inquiring on the ability of AGPs’ to transfer to humans. Producers are concerned that long term usage can lead to resistance to routine antibiotics.4 As a result, the industry is rethinking the usage of AGPs in animal feed globally, with European Union being the first to ban AGPs.
The farming community has started exploring the options – alternatives to antibiotics (AGPs). This has led to the reduction in such enteric health issues in poultry.5
Currently, there is more interest in natural antibiotic alternatives.
Criteria for Antibiotic Alternatives
An antibiotic alternative is expected to have the same beneficial effects that are offered by the AGP.
• Decrease pathogens (Clostridium)
• Anti-inflammatory effect
• Positive effect on beneficial bacteria of microflora
• Intestinal wall vitality
• Action on other pathogens like Salmonella and E. coli
• No resistance issues
• Improvement in animal performances
Commonly available alternatives to antibiotics are probiotics, prebiotics, organic acids, and essential oils. An ideal combination of two or more of the following products will be in a position to perform well or on par with AGPs.
1.PROBIOTICS Probiotics are defined as live microbial feed supplements, which beneficially affect the host animal by improving its intestinal microbial balance. Probiotics increase the normal microbiota population by the selective exclusion of specific pathogenic microbes in the gut. The suggested mechanisms of action of probiotics in improving poultry health and production include competitive exclusion, maintaining the integrity of the epithelial barrier, nutrient transfer and enhancing enteric immunity. The mode of action of a particular probiotic depends upon the generation. For example, the first generation probiotics act simply by competitive exclusion and the second generation probiotics act not only by competitive exclusion but also by way of producing antibacterial substances which have a specific action on pathogens.
Common probiotics used in poultry are Bacillus subtilis, Bifidobacterium spp and Lactobacillus spp. An ideal probiotic should be of host origin, non-pathogenic, resist gut conditions (acidic pH conditions), produce antimicrobial compounds, improve commensal bacteria growth, modulate the immune response, improve animal performance and withstand feed processing conditions.
2.ORGANIC ACIDS: Organic acids, such as lactic, acetic, tannic, fumaric, propionic, formic, citric, benzoic and butyric acids, etc., have been shown to exhibit beneficial effects on the intestinal health and performance of birds. Feeding organic acids may result in improved body weight gains and feed conversion ratio. A good range of organic acids with variable physical and chemical properties are available for poultry, for usage in water or feed. They are either available as single product or in combination. Recently there is more awareness and the industry prefers to use protected (encapsulated) organic acids as they have the advantage of sustained and targeted release in addition to reduced odour issues. Supplementation of organic acids can modify enteric bacterial population, so it is recommended to use it along with probiotics.
3.ENZYMES: For decades, enzymes have been widely used in poultry rations. Enzyme usage is quite important for poultry as feed contains corn and soya which have some anti-nutritional factors and enzyme inhibitors. To reduce the production cost, there is a tendency to use non-conventional feed raw materials. These raw materials are also known to have anti-nutritional factors and this practice also warrants the usage of enzymes. Enzyme supplementation reduces the pollutant potential of excreta. Enzymes also modulate the intestinal microbiota.
4.ESSENTIAL OILS: Different herbs and botanical products have been reported to impart beneficial effects on intestinal integrity, the gut environment and microflora through their biologically active components. The beneficial effects of essential oils may include stimulation of feed intake and digestive secretions, immunostimulation, antibacterial, antiviral, coccidiostatic, anthelmintic or anti-inflammatory effects and antioxidant effects.
5. BIOSURFACTANT: Fats and oils are used in animal diet. Studies have indicated that fat digestion is very low at an early age due to poor emulsification rather than deficiencies in lipase activity. Use of a biosurfactant is an effective way to improve absorption of oils and fats from feed through 1) enhanced emulsification leading to the formation of smaller fat/oil droplets in the small intestine, providing more surface area for lipase activity; 2) improved hydrolysis of fat; and 3) easier and smaller micelle formation due to the very low critical micellar concentration (CMC) of lysophospholipids. This improves the absorption of other nutrients like Vitamin A, D, E, and K, and carotenoids which are permeated into the intestinal villi and through the cell membrane of the intestinal cells. A biosurfactant can be used along with probiotics to improve performance, carcass yield, and litter quality.
6.MYCOTOXIN BINDER: Mycotoxins, which can be present in animal feed, can have serious negative effects on animal health. Under practical conditions no poultry feed is completely free from mycotoxins. Additionally, no feed is expected to contain only one mycotoxin. The adverse effects of mycotoxins on poultry are many indicating a clear and persistent danger. Several mycotoxin binders have been developed that prevent the toxic effects of mycotoxins on the animals consuming the contaminated feed. These materials bind with the mycotoxin(s) and prevent the negative effects on the animals consuming them.
7.PREBIOTICS: A prebiotic is defined as an indigestible diet component that usually influences the host animal through selective stimulation of growth and/or metabolic action of useful bacteria already present in the intestine and suppressing pathogenic bacteria. Prebiotics can be used in combination with probiotics to get the maximum advantage. Lactobacilli and Bifidobacteria spp. ferment prebiotics into short chain fatty acids, which increase in concentrations and reduce the enteric pH and inhibit the proliferation of certain pathogenic bacteria. In an investigation, all in-feed supplementation of a prebiotic, a probiotic, or an organic acid alone or in combination caused significant improvement in live weight of broilers in comparison with the control6. Therefore dietary prebiotics may be more fruitful when combined with probiotics.
An ideal prebiotic should not be hydrolyzed or absorbed, selectively enrich one or more commensal bacteria or beneficially alter the intestinal microbiota activities. The most common prebiotics used in poultry are oligosaccharides, including inulin, fructooligosaccharides (FOS), mannanoligosaccharides (MOS), galactooligosaccharides (GOS), soya-oligosaccharides (SOS), xylo-oligosaccharides (XOS), pyrodextrins, isomaltooligosaccharides (IMO) and lactulose.
8.BACTERIOPHAGES: These are viruses that infect bacteria and which replicate by utilizing the host’s metabolic system and then destroys the bacterial cell to release the new progeny phages into the environment. They are not reported to infect animal and plant cells, hence being potentially safe alternatives to antibiotics. Bacteriophages that have a specific action on Clostridium perfringens can be useful for NE control in chickens.