Effects of Dietary L-glutamate, L-aspartate, and Their Combination on Immune Responses and Intestinal Integrity of Weaned Piglets Challenged with Enterotoxigenic Escherichia coli F18

L-glutamate and L-aspartate are functional amino acids essential for intestinal functions and physiological metabolism. This study aimed to investigate effects of L-glutamate, L-aspartate, and their combination on immunity and intestinal integrity of weaned piglets challenged with enterotoxigenic Escherichia coli (ETEC). Sixty-five weaned pigs (7.59 ± 1.11 kg BW) were randomly assigned to five treatments (n = 13 per treatment): control (CON), CON + 1% glutamate (GLU), CON + 1% aspartate (ASP), CON + 1% glutamate + 1% aspartate (GAC), and CON + 50 mg/kg carbadox (ABX). All pigs were orally challenged with F18 ETEC (1010 CFU/dose/day) for three consecutive days. Serum was collected on d 0, 2, 4, 14, and 21 PI for inflammatory biomarker analysis using ELISA. Jejunal and ileal mucosa were collected on d 5 and 21 PI for assessing intestinal immunity and integrity via RT-qPCR. The study period lasted for four weeks, with a 7-day adaptation period and 21 days post-inoculation (PI). Data were analyzed using ANOVA in PROC MIXED of SAS with individual pig as the experimental unit. Compared with CON, GLU, ASP, or GAC groups decreased (P < 0.05) serum C-reactive protein on d 0 and 4 PI. Compared with CON, ASP, GAC, or ABX groups decreased (P < 0.05) serum IL-8 on d 2 PI, while GAC increased (P < 0.05) serum TNF-α on d 4 PI. Additionally, GLU, ASP, GAC, or ABX groups decreased (P < 0.05) serum haptoglobin compared with CON on d 14 and 21 PI. On d 5 PI, GAC-fed pigs showed highest (P < 0.05) jejunal and ileal IL1β and ileal IL17A expression among all groups. Interestingly, GAC-fed pigs tended to have highest (P < 0.10) jejunal TNFα but lowest (P < 0.10) ileal TNFα expression among all groups. On d 21 PI, GLU or ASP groups increased (P < 0.05) jejunal IL13 and tended to increase (P < 0.10) jejunal IL4 expression compared with CON. GAC-fed pigs also tended to increase (P < 0.10) jejunal IL4 and increased (P < 0.05) ileal IL4 expression compared with CON. Moreover, GLU-fed pigs had highest (P < 0.05) ileal TGFβ1 expression on d 21 PI among all groups. Compared with ABX, GAC-fed pigs tended to have lower (P < 0.10) jejunal OCDN expression on d 5 PI while higher (P < 0.10) jejunal MUC2 expression on d 21 PI. On d 5 PI, GLU, ASP, or ABX groups tended to decrease (P < 0.10) ileal CLDN1 expression compared with CON. On d 21 PI, GLU, ASP, or GAC groups had lower (P < 0.05) ileal ZO1 than ABX. In conclusion, glutamate and/or aspartate supplementation modulated immune responses and intestinal integrity, highlighting potential benefits to enhance disease resistance in ETEC-challenged weaned pigs.