Effects of dietary L-glutamate and L-aspartate supplementation on growth performance, severity of diarrhea, intestinal barrier integrity, and fecal microbiota of weaned piglets challenged with F18 enterotoxigenic Escherichia coli.

BACKGROUND: L-Glutamate and L-aspartate are functional amino acids that play pivotal roles in the cellular metabolic pathways of swine enterocytes. Therefore, this study aimed to investigate the effects of dietary L-glutamate and L-aspartate on growth performance, diarrhea severity, intestinal barrier integrity, and fecal microbiota of weaned piglets challenged with F18 enterotoxigenic Escherichia coli (ETEC). Weaned piglets were randomly assigned to seven dietary treatments, including unchallenged and ETEC-challenged controls, amino acid-supplemented groups, and an antibiotic control, to assess their responses to ETEC challenge. RESULTS: Supplementation with 1% L-glutamate or 2% L-aspartate enhanced growth performance, with significantly greater (P < 0.05) average daily weight gain and gain-to-feed ratio compared with the positive control group from d 0 to d 5 post-inoculation. Pigs fed with 1% or 2% L-aspartate had reduced (P < 0.05) diarrhea severity in ETEC-challenged pigs compared with the positive control group. The 1% L-aspartate supplementation also supported intestinal structure by increasing (P < 0.05) duodenal villi height and ileal villi width compared with carbadox supplementation. Additionally, 1% L-glutamate supplementation significantly improved (P < 0.05) resilience in ETEC-challenged pigs by reducing fecal shedding of β-hemolysin-producing bacteria compared with the positive control group on d 14 post-inoculation. Moreover, 1% L-aspartate supplementation promoted intestinal barrier integrity by significantly up-regulated (P < 0.05) the expression of ileal OCDN and ileal ZO-1 compared with the positive control group on d 14 post-inoculation. Interestingly, 2% L-aspartate supplementation altered the intestinal mucosa by down-regulating (P < 0.05) the expression of jejunal CLDN-1, while up-regulating (P < 0.05) the expression of ileal CLDN-1 compared with the negative control group on d 14 post-inoculation. Furthermore, L-glutamate supplementation significantly changed proportions of Firmicutes and Bacteroidota and showed the trend for enrichment in beneficial bacterial genera such as Bifidobacterium and Megasphaera in ETEC-infected pigs by d 14 post-inoculation. CONCLUSION: Supplementation with L-glutamate or L-aspartate promoted growth performance, supported gut health, and enhanced disease resistance in weaned pigs challenged with F18 ETEC. During the weaning period, L-glutamate or L-aspartate could potentially be considered conditionally essential amino acids, helping to alleviate weaning complications and reduce the need for antibiotic use in swine farming.