Several reports have been published describing positive effects of butyrate on gut health, supporting the use of butyrate as animal feed supplements. However, the effects elicited by dietary butyrate supplementation are variable, especially when looking at the physiological responses that may underlie improvements in animal performance. We hypothesized that at least a part of this variation could be attributed to differences in gastro-intestinal tract regions where butyrate was delivered by different butyrate-based feed additives. A total of 320 male day-old Ross 308 broilers were assigned to a control group or four groups that were fed products with different butyrate release characteristics: 1 g butyrate per kg of complete feed was administered, either as unprotected pure sodium butyrate, tributyrin, a combination of the two, or a fat-protected butyrate product. For 22 days, birds were fed a diet high in rapeseed meal, to provide a dietary challenge, and evaluated on digestive, microbial and immunological parameters. A higher butyrate presence in the proximal GIT was associated with a reduction of hindgut microbial diversity (P < 0.05) and a trend (P < 0.1) for a reduced apparent ileal digestibility of Ile, Leu, Phe, His and Lys. More- over, an increased expression (P < 0.05) of immunity-associated genes (TLR-4, MyD88, IL-6, CAT and NOS2) in the ileum or colon suggests an inflammatory status. A similar inflammatory signature was observed when butyrate concentrations were elevated in the mid-gut, although no sign of bacterial hindgut dysbiosis was detected in these birds. With increased hindgut butyrate levels a longer intestinal retention time (P < 0.05) and a tendency (P < 0.1) for FCR improvement and Met digestibility could be observed, without negative effects on caecal microbiota composition or inflammatory status. These results indicate that, at least under certain conditions, elevated butyrate concentrations in the fore- and midgut may induce negative effects on microbiota diversity and/or inflammation, as opposed to increased butyrate concentrations in the hindgut.
Overall, the data emphasize the importance of product-dependent butyrate release kinetics in investigating the effects of exogenous butyrate supplementation in broilers.