Effects Of Gaba On Intestinal SIgA Secretion And Its Mechanism In Weaning And ETEC Infected Piglets

The intestinal immune function of weaned piglets is undeveloped.Exogenous pathogens often induce intestinal infection and diarrhea in weaned piglets,which may easily lead to stunted growth and even death of piglets.Previous studies have shown that dietary supplementation with γ-aminobutyric acid(GABA)can regulate intestinal function in weaned piglets.SIg A(Secretory Immunoglobulin A)plays an important role in maintaining intestinal mucosal immunity and preventing intestinal infection,and GABA may regulate intestinal immune function through the secretion of SIg A.Therefore,37 21-day-old healthy DLY piglets(5.82 ± 0.86 kg)were randomly divided into two groups: the control group fed the basal diet(CON group,n = 18)and the experimental group supplemented with 40 mg/kg GABA in the basal diet(GABA group,n = 19).The experiment lasted 21 days.On the 14 th day of the experiment,6 pigs in each group were randomly slaughtered and sampled.The remaining piglets were fed with ETEC(Enterotoxigenic Escherichia coli)bacterial fluid to construct the infection model.On the 7th day after the modeling,another 6 pigs in each group were slaughtered and sampled.According to whether or not ETEC was inoculated,the experiment was divided into two stages: uninfected and infected.The growth performance,organ indices,amino acid levels and biochemical parameters of serum,intestinal SIg A concentration,expression of Ig A-inducing cytokines,gut microbiota composition and intestinal metabolites were analyzed at the end of each stage.The main results are as follows: 1)GABA had no significant effects on body weight gain,average daily gain,average daily feed intake,feed conversion efficiency and organ index in weaned and ETEC infected piglets(P > 0.05).2)In weaned piglets,GABA significantly increased serum histidine concentration and serum calcium content and decreased aspartic acid concentration(P < 0.05).GABA had no significant effect on serum amino acids in ETEC infected piglets(P > 0.05),but decreased serum albumin level(P <0.05).3)GABA significantly increased the content of SIg A in the jejunum of weaned piglets and ETEC infected piglets.Moreover,it also significantly increased the expression of SIg A in the ileum of weaned piglets(P < 0.05).4)GABA significantly increased the protein or m RNA expression of IFN-γ,IL-1β,IL-4,IL-13 and IL-17 in the jejunum of weaned piglets(P < 0.01).5)GABA had no significant effect on the gut microbial Alpha diversity of weaned piglets(P > 0.05),but significantly reduced the relative abundance of Phascoarctobacterium and Butyricicoccus of weaned piglets,and increased the relative abundance of Enterococcus of weaned piglets(P < 0.05).In ETEC infected piglets,the relative abundances of Bacteroides and an unidentified Ruminococcaceae were significantly increased by GABA treatment(P < 0.05).6)GABA had a greater effect on fecal metabolite composition in weaned piglets.10 differential metabolites,including hydroxylamine,and 6 related metabolic pathways,were identified in weaned piglets,while GABA had less effect on fecal metabolite composition in ETEC infected piglets.7)Correlation analysis found that in feces of weaned piglets,the content of hydroxylamine was positively correlated with the relative abundance of Enterococcus,but negatively correlated with the relative abundance of Phascolarctobacterium and Butyricicoccus.In feces of ETEC infected piglets,the content of1,2,4-benzenetriol was positively correlated with the relative abundance of Bacteroides,and the content of oleic acid was negatively correlated with the relative abundance of unidentified Ruminococcaceae.In conclusion,supplementation of 40 mg/kg GABA could enhance intestinal immune barrier function of weaned piglets by promoting intestinal SIg A secretion.GABA increasing SIg A secretion may be related with gut microbial metabolic changes,especially Enterococcus.However,further researches are warranted to reveal the specific role of Enterococcus.