The chicken gut contains a diverse population of bacteria, viruses, fungi, and protozoa, known as the gut microbiota. The major development of this community starts fromhatching onward, as birds come into contact with the farm environment, people, andfeed. Pathogenic and commensal bacteria that are harmful to humans can establishthemselves in early life, so steps to avoid exposure to these must be in place. Themicrobiota performs multiple roles for the bird, including the exclusion and inhibitionof pathogens, the development of the immune system and intestinal tissues, and thedigestion of some non-digestible components of the diet. If digestion or absorptioniscompromised, it can lead to an imbalance or overgrowth of the microbiota, whichmayresult in reduced welfare, health, and performance. Gut stability is strongly shapedbymanagement and environmental conditions throughout the flock cycle.

Optimizing gut health starts before the chicks arrive. Best practice is to remove all litterand dust, before washing with an approved sanitizer. The outside of the house shouldalso be cleaned to prevent reintroduction of microorganisms. Water is a crucial routeformicrobial entry, and special attention should be given to thorough cleaning and sanitation of the water system. Use a 24-hour hydrogen peroxide treatment to breakupthe biofilm. Then, after flushing, apply a weak acid, such as citric acid, to break upanyremaining scale. Maintain a sanitizer in the system during clean-out and flush againimmediately before chick arrival to provide the cleanest possible water to the chicks. During the life of the flock, a suitable sanitation program (e.g., hydrogen peroxide, chlorine, or chlorine dioxide) should be used to treat the birds' drinking water.

The house should be disinfected with an approved product, and the effectiveness verifiedby bacterial swabbing and plate counts. A strong rodent control programis essential; clean uniforms and boots should be provided. Ideally, footwear should be changedat theentrance to each house to minimize the risk of contamination from the outside
environment.

The villi lining the intestinal tract of modern-type broilers are significantly longer thanthose of heritage breeds, allowing modern birds to absorb nutrition more effectively. During brooding, the villi undergo rapid development, with the intestinal tract developingfour times faster than any other tissue, meaning disruptions can have lifelong effects. During brooding, the yolk sac is absorbed, gut tissues grow, immunity develops, andthemicrobiota begins to evolve. Ensuring early access to feed and water, confirmingchickcomfort, and achieving target growth are the keys to success. Retained yolk sacs, blackening of the gizzard surface, and pasty vents are common signs of sub-optimal
brooding, which can be linked to poor gut development. Because this early phaseis foundational, any nutritional or environmental challenge at this stage can permanentlylimit the flock's performance potential.

After brooding, the gut enters a transitional phase during which the microbial balanceshifts. Several factors can impact the outcome of these changes:

    - Diet – Feed changes, poor raw material quality, including the presence of mycotoxins, and physical feed quality, as well as poor feed availability, canall disturb microbiota balance. Increased fines in the feed shorten gizzard dwell times and stimulate water consumption, resulting in inadequate digestionandrapid gut transit. 

    - Management – Sub-optimal environmental management, especially duringperiods when the birds can come under pressure, such as vaccination, partial depopulation, and feed change, can destabilize the microbiota, causing its
composition to fluctuate. In some cases, this can lead to dysbiosis. Proactiveplanning involving gut health additives may help maintain gut health during these times.

    - Environment – Heat stress can cause reduced feed intake, and have a direct impact on gut health. This results in poor gut function and inefficient nutrient absorption. Inadequate ventilation allows moisture, carbon dioxide, and ammoniato accumulate, harming litter quality and increasing the risk of dysbiosis andopportunistic infections. Excessive ventilation can also cause birds to becomeinactive, reducing their feed intake. Maintaining both air quality and bird activityis therefore essential to protect gut function.

    - Biosecurity – A lack of effective biosecurity increases the risk of infectioninaflock. Depending on the pathogen, this infection can have a direct impact onthegut microbiota and gut health, or an indirect impact due to changes in birdbehavior and reduced feed intake. More broadly, bird performance may becompromised during an infection as nutrients are redirected away fromgrowthtothe immune system.

Eventually, the gut microbiome will reach a mature balance. The principles discussedabove (see Figure 1) remain essential, as maintaining this balance is key to ongoingperformance. If there is a change in the color or consistency of the fecal or cecal droppings, the birds are likely undergoing a gut health challenge. Given the varietyof non-antibiotic gut health products available (probiotics, competitive exclusion products, organic acids, phytogenics, etc.), it is vital to investigate the underlying cause of the issue and choose a product whose mode of action matches the specific gut challengeinyour farm or operation. The use of antibiotics can be highly effective in reducingpopulations of pathogenic bacteria, but it can also impact beneficial gut bacteria. Antibiotics should be used sparingly and only under the guidance of a veterinarian. Follow up with a gut health additive may help rebalance the gut after antibiotics.