Effects of dietary gamma-aminobutyric acid supplementation on amino acid profile, intestinal immunity, and microbiota in ETEC-challenged piglets

Enterotoxigenic Escherichia coli (ETEC) infection is the most common cause of diarrhea in piglets, and ETEC could increase intestinal gamma-aminobutyric acid (GABA)-producing bacteria to affect intestinal immunity. However, the effect of GABA on ETEC-infected piglets is still unclear. This study aims at investigating the impact of dietary GABA supplementation on the growth performance, diarrhea, intestinal morphology, serum amino acid profile, intestinal immunity, and microbiota in the ETEC-infected piglet model. Eighteen piglets were randomly divided into two groups, in which the piglets were fed with a basal diet with 20 mg kg-1 GABA supplementation or not. The experiment lasted for three weeks, and the piglets were challenged with ETEC K88 on the fifteenth day. The results showed that dietary GABA reduced the feed conversion ratio, promoted the kidney organ index but did not affect the diarrheal score and small intestinal morphology in ETEC-challenged piglets. Ileal mucosal amino acids (such as carnosine and anserine) and serum amino acids (including threonine and GABA) were increased upon GABA supplementation. GABA enhanced ileal gene expression of TNF-α, IFN-γ, pIgR, and MUC2, while inhibited the ileal expression of IL-18 in ETEC-challenged piglets. GABA supplementation also highly regulated the intestinal microbiota by promoting community richness and diversity and reducing the abundance of the dominant microbial population of the ileal microbiota. Collectively, GABA improves growth performance, regulates the serum amino acid profile, intestinal immunity, and gut microbiota in ETEC-challenged piglets. This study is a fine attempt to reveal the function of GABA in ETEC-infected piglets. It would contribute to the understanding of the roles of exogenous nutrition on the host response to ETEC infection.