A key factor in the biological performance and efficiency of food producing animals, turkeys in particular, is the health of the gastrointestinal (GI) tract. A healthy GI tract ensures optimal digestion and absorption of nutrients.
In recent years there has been a concern that the use of antimicrobials in food producing animals is contributing to the rise in prevalence of drug resistant bacteria. In response to this concern, growth promoting antibiotics were withdrawn from farming practices across the EU (EC Regulation No. 1831/2003). This move has been mirrored by the FDA in the USA, where efforts have been made to voluntarily phase out the use of medically important antimicrobials as growth promotants (FDA guidance notes 209 and 213, 2012/13). It is likely that the use of antimicrobials within the poultry industry will continue to be reduced resulting in the need for alternative strategies to be developed. Within the poultry industry there are many initiatives aiming to understand gut health and how it can be influenced in the absence of antimicrobials. These initiatives have shown that there is a need for further characterisation of the intestinal microbiota along with more research to understand their interaction with the host and the external environment.
Balanced intestinal microbiota: key in poultry husbandry
The development and maintenance of optimal intestinal health is heavily reliant upon the acquisition and maintenance of a balanced intestinal microbiota, this has become one of the key topics in poultry husbandry. Bacteria reside in all known habitats, therefore it is not surprising that evolution has resulted in symbiotic relationships between an animal and its microbial residents. The intestinal microbiome of an animal is a complex community of micro-organisms dominated by bacteria. The bacteria in the intestinal tract vary in density and species in the different compartments of the gut depending on the local environment. The gut microbiota plays a vital part in the health and wellbeing of its host by providing a number of benefits. The intestinal microbiota aids digestion, protects against pathogens, produces nutrients and plays a role in the development and maturation of the gut tissues and immune system.
Gut is a dynamic entity - changing as the bird ages
Intestinal health is a complex area due to the wide range of management and health related factors which can impact upon the function of the gut. The gut and its resident microbiota are a dynamic entity which changes as the bird ages; understanding these changes is key to maintaining intestinal integrity to ensure optimal bird growth. The development of the gut starts during incubation and continues once the poult hatches out of the egg. During the first 2 weeks of life, the gut tissues undergo rapid development and the villi at the gut surface elongate. During the initial villi growth the villi reach approximately 50% of their final length due to the presence of 2 growth centres: 1 at the base of the villi and 1 in the middle of the villi. After this initial period only the growth centre at the base of the villi persists and the cells in the growth centre in the middle of the villi stop dividing. If villus growth is impaired during the first 2 weeks of life it can have long term consequences for the absorptive capacity of the gut in the adult bird. Optimal brooding conditions with easy access to feed and clean water are essential for optimal post–hatch gut development and long term gut health of the flock. Another key factor in the development of the villi is stimulation by the intestinal microbiota; villus length has been shown to be stimulated by lactobacilli which are the bacteria which dominate the small intestine. Even though the GI tract of the developing poult in ovo is not completely sterile, the majority of colonisation of the gut of the poult occurs post hatch. Source of bacteria include the farm environment, the feed, the water supply and the litter onto which the birds are placed. In most poultry production systems across Europe, poults are placed on to fresh litter in a disinfected shed having hatched in a clean hatchery. Disinfection and sanitation are important for the control of pathogens, however it can negatively influence the development of the gut due to a delay in the maturation of the gut microbiota. The application of probiotics and competitive exclusion agents in day old poults has been shown to aid the maturation of the intestinal microbiota and enhance the development of the gut tissues. A properly developed intestinal microbiota can help protect against pathogens which could impact upon animal health and food safety. If the GI tract is compromised by gut pathogens, the function of the GI tract is impacted upon thus reducing absorption and efficiency which causes an increase in feed conversion rate.
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A delicate balance
There is a delicate balance between the host, the intestinal microbiota, the intestinal environment and dietary compounds. An imbalance in this relationship can alter the composition of the intestinal microbiota. The shift in microbial populations can have a negative effect on the host leading to poor growth and poor performance – this is seen in cases of dysbacteriosis. Dysbacteriosis is a digestive condition of poultry and has been broadly described as an overgrowth of the intestinal microbiota leading to non-specific enteritis which can result in wet litter. Its aetiology is not fully understood but it is often seen following events which can cause physical or physiological stress on the birds such as feed changes and handling or moving the birds. Stress induced enteric upset is seen in many different animal species and has been shown to be linked to the increase in growth of certain bacterial species. The hormones released during stressful events enter the gut and the activity of certain bacteria, such as E. coli and Salmonella spp., increases which can lead to enteritis and increased susceptibility to disease. Bacteria have a preferred range of nutrient sources, as such the composition of the intestinal microbiota is influenced heavily by dietary formulation. During the life of a turkey flock there are a number of feed changes where there is a shift in energy and protein densities of diets; this invokes a change in the micronutrients available for the gut microbiota. In the event of a feed change, the gut microbiota can become unbalanced as the response to the change varies across the bacterial population and the result can be overgrowth of certain bacteria leading to diarrhoea. It is common practice to treat the resultant dysbacteriosis with antimicrobials to restore the balance. However, the use of direct fed microbial products or organic acids over a feed change can inhibit the overgrowth of the less favourable bacteria during feed changes and maintain gut integrity to reduce the likelihood of dysbacteriosis occurring.
Prepare bird for changes
The key to the maintenance of intestinal health is understanding how the intestinal microbiota changes at key points throughout a bird’s life and how it is possible to prepare the bird for these changes. The combination of practical field experience from poultry producers and veterinarians with laboratory research into the relationships between the host and its microbiota is likely to reveal further ways by which enteric health can be improved.
References available upon request.