Gut antibacterial effects of C7 and C9 carboxylic acids in the diet of piglets

The antibacterial effects of odd-numbered medium-chain fatty acids (MCFA), such as C7 and C9 carboxylic acids, are poorly described and, hence, their potential as a feed additive for weaned piglets has not been explored. First, the antimicrobial activity was tested in in vitro incubations simulating the digestion in the stomach (pH 3), duodenum (pH 5), and ileum (pH 7) at 0, 17.5, 35.0, and 70.0 mmol/L carboxylate and compared with even-numbered MCFA. All compounds showed a significant reduction of analyzed bacterial counts compared with the control, in many cases >2 log reduction up to complete disappearance, depending on pH and dose. At pH 3 and 5, C6 through C9 carboxylic acids were equally effective against coliforms, whereas C10 was less effective. The activity against lactobacilli and streptococci was higher at the lower pH and increased with chain length. The antimicrobial effects of C7 and C9 carboxylic acids were, in most cases, in between or, in one case, better than that of their respective neighboring even-numbered MCFA. Next, an equal mixture of C7 and C9 carboxylic acid was fed to weaned piglets at 0, 0.1, 0.2, and 0.4% carboxylic acids in the diet for 42 d (8 pen replicates with 6 pigs each). At d 13/14, 1 piglet per pen was sampled to determine major gastric and proximal and distal small intestinal bacterial groups and histomorphological characteristics. Numerical improvements of animal performance for all supplemented diets were observed (P > 0.05) and this corroborated with a trend for longer villi in the proximal small intestine (P = 0.082). The highest dose tended to reduce streptococci in the stomach contents (P = 0.079). In vitro, C7 and C9 carboxylic acids demonstrated clear and significant antibacterial effects against the major bacterial groups in the stomach and small intestine. In the postweaning performance trial, they showed potential to ameliorate performance.