Poultry Gut Health Management to control Coccidiosis and Necrotic Enteritis

A key factor in the biological performance and efficiency of food producing animals is the health of the gastrointestinal (GI) tract.  A healthy GI tract ensures optimal digestion and absorption of nutrients.  Within the poultry industry there are many initiatives aiming to understand gut health and how it can be influenced to improve efficiency and reduce disease.  These initiatives have shown that there is a need for further characterisation of the gut microbiota along with more research to understand their interaction with the host and the external environment.

The development and maintenance of optimal gut health is heavily reliant upon the acquisition and maintenance of a balanced gut 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 gut 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 gut microbiota aids digestion, protects against pathogens, produces nutrients and plays a role in the development and maturation of the gut tissues and immune system.  Within the gut microbial community there are a number of opportunistic pathogens which have the potential to cause disease if they have the opportunity to translocate across the gut barrier.  The gut barrier is essentially a single layer of epithelium which prevents bacteria from passing into the gut mucosa.  If this barrier is compromised then gut inflammation can occur.   

Globally the most common and significant intestinal disease in poultry is coccidiosis.  This disease is caused by members of the protozoal genus Eimeria, and is estimated to cost the global poultry industry in the region of £1.8 billion a year.  This parasite is ubiquitous in any poultry rearing environment with infection causing economic loses. The impact of the parasite on a bird is dependent on the level and duration of infection.  A high level of infection will cause clinical disease causing major pathological damage to the GI tract and, in severe cases, death of the bird.  In less severe subclinical infections there is generally no increase in mortality although there can be disruption to normal gut function.  The consequence of subclinical infection is a loss in feed efficiency and poor growth due to damage to the gut wall and a reduction in the absorption of nutrients.  During infection with coccidiosis the gut barrier is compromised which enables the translocation of bacteria into the gut mucosa and bloodstream, this can lead to secondary infections.

One of the most commonly recognised consequences of damage to the gut epithelia is the onset of necrotic enteritis caused by Clostridium perfringens; a normal member of the gut microbiome. Secondary infections resulting from damage to the gut wall are not isolated to the intestinal tract but can also be seen systemically following a bacteraemia.  Once in the bloodstream, bacteria can infect the liver, the heart or the joints leading to increased mortality or lameness.  This highlights the importance of ensuring the development and maintenance of the gut is supported throughout the life of the bird.

The development of the gut starts during incubation and continues once the chick hatches out of the egg.  During the first week 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 two growth centres: one at the base of the villi and one 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 two 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 gut 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 chick in ovo is not completely sterile, the majority of colonisation of the gut of the chick occurs post hatch.  Source of bacteria include the farm environment, the feed, the water supply and the litter onto which the birds are placed.  The application of direct fed microbials, organic acids, prebiotics to day old chicks have been shown to aid the maturation of the gut microbiota and enhance the development of the gut tissues.  A properly developed gut microbiota can help protect against pathogens which could impact upon animal health and food safety.  The maintenance of 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 and preparing for these changes is key to maintaining gut integrity to ensure optimal gut function.  It also has to be remembered that in addition to the potential to reduce enteric disease, ensuring optimal gut development and functionality is important to maximise the expression of genetic potential for growth, FCR and liveability.