Organic acid-preserved grain improves growth and gut health in weanling pigs fed zinc oxide free diets

The effects of organic acid (OA)-preserved grain and zinc oxide (ZnO) supplementation on post-weaning (PW) piglet performance and intestinal health were evaluated in a 2 × 2 factorial study. Ninety-six piglets (28 days old) were allocated to four diets: dried grain, OA-preserved grain, dried grain + ZnO, and OA-preserved grain + ZnO, for 35 days. Diets contained 600 g/kg grain (450 g/kg wheat, 150 g/kg barley). On day 10 PW, 28 piglets (n = 7/treatment) were euthanised for small intestinal morphology, gene expression, microbial, and volatile fatty acid (VFA) analyses. OA-preserved grain reduced dietary Ochratoxin A and Deoxynivalenol concentrations and increased average daily gain (P < 0.05), but provided no additional growth benefit when combined with ZnO. ZnO increased feed intake, body weight, colonic Lactobacillus abundance, and villus height-to-crypt depth ratio, while reducing faecal scores and colonic branched-chain fatty acids (P < 0.05). OA-preserved grain increased ileal Faecalibacterium and reduced Escherichia populations, and downregulated duodenal IL17 and ileal FOXP3 expression (P < 0.05). ZnO broadly suppressed pro-inflammatory cytokines and upregulated nutrient transporter genes (SLC15A1, SLC16A1). These findings indicate that OA-preserved grain improves growth and gut health but does not fully replace ZnO in mitigating PW diarrhoea.