This study aimed to determine the effects of propionic acid (PA) as a grain preservative and feed supplement on piglet growth and health post-weaning (PW). Grain was dried or preserved with 4 kg/tonne of PA post-harvest, and PA was supplemented or not at 4 kg/tonne during diet manufacture. Ninety-six weaned piglets were assigned to a 2 × 2 factorial design: (T1) dried grain diet, (T2) preserved grain diet, (T3) dried grain diet with PA and (T4) preserved grain diet with PA for 35 days. Each diet contained 450 g/kg of wheat and 150 g/kg of barley, either dried or preserved. Ten days PW, 28 piglets (n = 7) were euthanised for sample collection. Preserved grain reduced ochratoxin A and deoxynivalenol levels and increased body weight, average daily gain and average daily feed intake compared to dried grain (P < 0.05).
Supplementing PA increased the relative abundance of Faecalibacterium in the dried grain diet, but reduced Faecalibacterium in the preserved grain diet. Supplementing PA reduced ileal Escherichia in dried grain, but increased Escherichia in preserved grain (P < 0.05). Supplementing PA increased colonic Clostridium in preserved grain but had no effect on Clostridium in dried grain (P < 0.05). Supplementing PA reduced infl ammatory cytokine expression in the duodenum (IL1B/CXCL8/IL17/IL22/TLR4), jejunum (IL17/IL22) and ileum (IL22) compared to non-PA supplemented diets (P < 0.05). In conclusion, preserved grain improved grain quality, microbial populations and growth. Supplementing PA reduced intestinal infl ammatory markers, suggesting potential as a feed additive in stress-inducing commercial settings.