Dietary supplementation with benzoic acid improves apparent ileal digestibility of total nitrogen and increases villous height and caecal microbial diversity in weaner pigs

The purpose of this study was to evaluate the effects of feeding two different levels of benzoic acid (BA) and three different levels of inulin (IN) on weaner pig performance, coefficient of apparent ileal digestibility of total nitrogen (CAID_N)_, small intestinal structure, diversity of caecal microbiota, indices of bacterial fermentation, incidence of post-weaning diarrhea (PWD) and enterotoxigenic Escherichia coli (ETEC) shedding. Ninety-six female pigs (Large White×Landrace) aged 21±3d and weighing 5.9±0.08kg (mean±S.E.) were used in a 2×3 factorial experiment, with the respective factors being supplementation of BA (0 and 5g/kg; referred to as BA0 and BA5, respectively) and (or) IN (0, 40 and 80g/kg; referred to as IN0, IN40 and IN80, respectively) in the diet. In week 2, pigs eating BA5+IN80 gained as an average 53 and 50g/d more weight (P=0.044) than pigs eating the BA0+IN80 and BA5+IN0 diets, respectively. Benzoic acid increased average daily gain (ADG) and feed intake (FI) in the third week after weaning (P=0.006 and P=0.037, respectively) and overall (P=0.026 and P=0.024, respectively). Feeding the BA-supplemented diets increased the CAID_N (P=0.003) and villous height (P=0.05), and tended to improve the villlus:crypt ratio (P=0.10). A significant BA x IN interaction increased bacterial diversity in digesta (P=0.005) and the proportions of propionic acid (P=0.028) in the caecum. Inulin supplementation decreased (P=0.001) the proportions of acetic and increased (P=0.001) the proportions of valeric acids in the caecal and proximal colon digesta. Benzoic acid tended to decrease levels of lactic acid (LA; P=0.063) and proportions of branched-chain fatty acids (BCFA) in the caecal (P=0.091) and proximal colon (P=0.099) digesta. The molar proportion of BCFA in the proximal colon was influenced by IN (P=0.012), with highest proportions found in pigs eating BA0+IN80 and lowest proportions found in pigs eating BA5+IN40 diets. The incidence of PWD was sporadic, low and unaffected by diet. These data imply that feeding weaner pigs a BA-supplemented diet has potential to improve ADG, FI, CAID_N and gastrointestinal development, and increase bacterial diversity in the caecum.