Gallic acid-usnic acid complex alleviates necrotic enteritis in broilers by remodeling gut microbiota and strengthening intestinal barrier.

This study investigated the effects of a dietary supplement containing a gallic acid-usnic acid complex (GU) on broilers challenged with necrotic enteritis (NE). A total of 324 one-day-old Arbor Acres broilers were randomly assigned to three groups with 6 replicates of 18 broilers each: (1) basal diet (NC); (2) basal diet + NE challenge (PC); (3) basal diet + NE challenge + 500 mg/kg GU (GU). The NE challenge was induced by oral administration of a coccidial quadrivalent vaccine on day 12, followed by Clostridium perfringens type A on days 17-20. The results showed that GU supplementation significantly improved growth performance, as evidenced by increased body weight and average daily gain (ADG) compared to the PC group at 21, 28, and 42 days of age (P < 0.05). GU effectively inhibited key pathogenic microbes through its antimicrobial and antiparasitic actions, as evidenced by reduced fecal coccidial oocyst shedding and decreased cecal Clostridium perfringens colonization compared to the PC group. It enhanced intestinal barrier function via improved ileal villus structure, increased goblet cell density, and upregulated the expression of the tight junction protein Claudin-1. GU significantly reduced the concentrations of interleukin-1β (IL-1β) and lipopolysaccharide (LPS) in the ileum and serum (P < 0.05), downregulated the mRNA expression of nuclear factor-kappa B (NF-κB) and myeloid differentiation primary response 88 (MyD88) (P < 0.05). Furthermore, GU modulated the gut microbiota by increasing α-diversity and enriching beneficial bacteria including Cyanobacteria, Bacteroides coprocola, and Parabacteroides merdae. In conclusion, GU alleviates NE in broilers by modulating the gut microbiota, inhibiting pathogenic microbes, strengthening the intestinal barrier, and mitigating inflammation and oxidative stress, thus presenting a promising nutritional strategy for sustainable broiler production.