Alanyl-Glutamine Dipeptide Mitigates E. coli-Induced Pathogenesis in Hy-Line Brown Hens: Mechanistic Insights into Microbiome Modulation, Antioxidant Response, and Intestinal Integrity

Escherichia coli (E. coli) infection in poultry triggers severe diarrhea and intestinal damage, ultimately disrupting gut function. Alanyl-glutamine (Aln-Gln) dipeptide not only exhibits potent gut-repairing efficacy but also restores barrier integrity and counters E. coli pathology through mucosal healing and immune modulation. In this study, the effects of Aln-Gln on microbiome modulation and intestinal integrity in growing hens challenged with E. coli were evaluated. The 250 healthy, Hy-line brown pullets (42 days old) were randomly divided into 5 experimental groups, each having five replicates of 10 chicks. Five dietary groups include a basal diet without added Aln-Gln and no E. coli challenge (NC), a basal diet without added Aln-Gln and orally administered 2.0 × 104 CFU/mL E. coli suspension (C), a basal diet added 0.1% Aln-Gln and orally administered 2.0 × 104 CFU/mL E. coli suspension (G1), a basal diet added 0.2% Aln-Gln and orally administered 2.0 × 104 CFU/mL E. coli suspension (G2) and a basal diet added 0.3% Aln-Gln and orally administered 2.0 × 104 CFU/mL E. coli suspension (G3). The results showed that dietary supplementation with 0.2% or 0.3% Aln-Gln effectively mitigated the adverse effects of an E. coli challenge, restoring body weight and feed intake to levels comparable to non-challenged controls. Aln-Gln supplementation (0.2–0.3%) reduced diarrhea severity, restored ileal morphology (villus height, crypt depth), improved antioxidant enzyme activity (GSH-Px, SOD), and reduced oxidative markers (MDA) (p < 0.05). Aln-Gln decreased pro-inflammatory (IL-1β, IL-6, NO) and apoptotic (BAX) responses (p < 0.05) and enhanced barrier integrity. It rebalanced gut microbiota by suppressing pathogenic Clostridium (75% in C vs. 29.9% in G3) and increasing beneficial Lactobacillus in G2/G3 compared with C. These findings demonstrate Aln-Gln as a beneficial dietary additive that restores growth performance and gut integrity; reduces diarrhea severity, inflammation, and apoptosis; and improves antioxidant status as it rebalances gut microbiota.