effects of butyrate given the diversity of cell types and pH conditions encountered throughout the GIT of poultry, and the differences in microbiota composition in the different gut segments; our understanding of the mode of action of butyrate might be hampered. Characterisation of existing additives and development of targeted-release formula- tions are, therefore, important to gain insight in the different physiological effects butyrate can elicit in broiler chickens.
Butyrate in different GIT segments In broilers, Moquet et al. (2018) showed that butyrate pres- ence in the digesta of distinct GIT segments of broilers leads to differential effects on digesta retention time, gut morphol- ogy and proteolytic enzymatic activities, ultimately resulting in differences in protein digestibility. In their study, the fol- lowing was observed: The apparent ileal digestibility of me- thionine tended to increase when butyrate and/or propion- ate was present in colonic and caecal contents, possibly due to modifications of GIT development and digesta transit time. Also, butyrate presence in the digesta of the crop, proven- triculus and gizzard, on the contrary, tended to decrease the apparent ileal digestibility of several AA. In addition, butyrate presence beyond the gizzard elicited an anorexic effect that might be attributable to changes in intestinal enteroendo- crine L-cells secretory activities. The research shows that ef- fects of butyrate on digestive processes are conditioned by
the GIT segment wherein the molecule is present and indi- cates its influence on digestive function and bioavailability of AA.
Uptake, metabolism and immune response In his research work Moquet observed that butyrate uptake is a passive process in the gastric region while being facilitated by putative (sodium-dependent) monocarboxylate transport- ers in the small and large intestine. Increasing digesta bu- tyrate concentration in the gastric region seemed to increase the β-oxidation of lipids. A similar effect was observed in the ileum and colon. Increasing digesta butyrate concentration in the duodenum seemed, however, to promote glycolysis. Bu- tyrate has, therefore, a location-dependent effect on energy metabolism in the gut. Despite such specificities, intracellular butyrate concentration remained low across GIT segments and diets. Butyrate increased the expression of preprochole- cystokinin in the duodenum. This may explain the anorectic effect of dietary butyrate supplementation in poultry.
Immune response A study in broilers showed that butyrate presence in the di- gesta of distinct GIT segments leads to different immune re- sponses when broilers are subjected to non-infectious im- mune challenges. They observed that natural antibody levels are conditioned by the GIT segment wherein the molecule is present.
▶ POULTRY WORLD | No. 2, 2019 17
Butyrate exerts not only direct effects on bacte- ria, but also elic- its effects on the host that may affect microbio- ta composition indirectly.
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