Butyrate in broiler diets: impact of butyrate presence in distinct gastrointestinal tract segments on digestive function, microbiota composition and immune responses

The release profile of experimental and commercially available butyrate feed additives was measured in an in vitro study. Butyrate derivatives having markedly different release profiles were used in two in vivo experiments to inverstigate the effect of butyrate presence in distinct GIT segments on digestive processes, microbiota composition and immune responses of broilers. These studies have led to the following conclusions:

• Unprotected butyrate is active in the gastric region of broilers. Tributyrin is active in the small intestine. There is an important variability of release profiles among fat-coated butyrate additives that have similar macroscopic shapes, colours and particle sizes. Some fat coated butyrate additives can extend the effect of butyrate to the colon and ceca.

• Butyrate when present in the gastric region of poultry induces inflammation and dysbiosis in the colon and ceca.

• Butyrate when present in the small intestine increases IgY NAb titers in peripheral blood and induces inflammation in the colon and ceca.

• Butyrate when present in the colon and ceca of broilers increases intestinal retention time in a manner that can improve the digestibility of nutrients.

• Transport of butyrate across the epithelium is a passive process in the gastric region and an active process in the small intestine and colon. The extent to which butyrate is oxidized in the gut of poultry appears to vary depending on the GIT segment considered. Intracellular butyrate concentration is low in the GIT and butyrate does not pass into the peripheral circulation.

Butyrate does not always elicit positive effects for the gut health of broilers. Such findings support a shift in paradigm, from butyrate being a beneficial molecule to butyrate having effects that may be positive or negative depending on the GIT location considered and the concentration present. Broilers appear to react strongly to increases in digesta butyrate concentration in GIT segments where butyrate production is normally limited (crop, proventriculus, small intestine). Tolerance for the presence of butyrate in the digesta in the gastric region and small intestine may be low. The detrimental effects reported in the present thesis may be related to a strong response of broilers to butyrate signaling in such GIT segments. In contrast, GIT segments where normally butyrate production is substantial (colon and ceca) appear to have a higher tolerance for the presence of butyrate in digesta.