A. The effects of a high-fiber diet on S. au-induced mastitis in mice were investigated. Mice were separated into four groups, including control, high-inulin (HI), S. au and HI + S. au groups (n = 6 per group), and fed with control or HI diet for three weeks followed by S. au-induced mastitis. B. The depletion of the gut microbiota by antibiotic cocktail (ABX) was performed to investigate the role of gut microbiota in HI diet-mediated protective effects on S. au-induced mastitis (n = 6 per group). C. Fecal microbiota transplantation (FMT) from control- (CF) or HI diet- (HIF) treated mice was used to confirm the role of gut microbiota (n = 6 per group). D. The effects of butyrate, propionate and acetate on S. au-induced mastitis were investigated (a) and HDAC inhibitors, including RGFP966 and NA, were used to investigate the underlying mechanism (b) (n = 6 per group).