Harnessing apidaecin capability to improve intestinal health and inhibit Salmonella Typhimurium transmission in laying hens

Apidaecin (Api), an antimicrobial peptide, exhibits in vitro efficacy against Salmonella Typhimurium (S. Typhimurium) and enhances broiler growth performance via modulation of intestinal barrier function. This study evaluated the effects of dietary apidaecin on intestinal health in laying hens and its potential to mitigate S. Typhimurium infection and egg contamination. A total of 288 Hy-Line grey layers (45-week-old) were randomly allocated to 4 dietary treatments (6 replicates per treatment, 12 birds per replicate). Basal diet supplemented with 0 (Con), 300(Api300), 500(Api500), or 700(Api700) mg/kg apidaecin for 12 weeks. Based on intestinal barrier function assessment, 18 hens each from the Con and Api 500 groups were selected for S. Typhimurium challenge. Apidaecin's inhibitory effects on S. Typhimurium adhesion and invasion were further assessed using an in vitro intestinal epithelial cell model. Data were analyzed using one-way ANOVA with Duncan's post-hoc test for multi-group comparisons and independent t-tests for two-group comparisons. Results indicated that daily feed intake, crypt depth and villus height to crypt depth ratio (V/C) of intestinal tract showed a quadratic response (P < 0.05) to increasing levels of apidaecin supplementation. Apidaecin (500 mg/kg) significantly reduced feed intake (1.76%), jejunal (29.04%) and ileal crypt depth (31.04%), while increasing duodenal (24.41%), jejunal (45.15%) and ileal V/C (36.39%) versus control (P < 0.05). Apidaecin significantly increased (P < 0.05) the relative abundance of beneficial short-chain fatty acid-producing bacteria (e.g., Phascolarctobacterium and Desulfovibrio), while reducing (P < 0.05) the relative abundance of enteritis-associated pathogens (e.g., Actinobacillus) of cecum. These beneficial effects were maximized at the 500 mg/kg diet level. Post-challenge, Api 500 hens exhibited increased (P < 0.05) jejunal and ileal V/C ratios and ileal secretory IgA expression compared to controls. Furthermore, apidaecin supplementation significantly reduced (P < 0.05) S. Typhimurium loads in the ileum, spleen, liver and on eggshells. In vitro assays confirmed apidaecin's direct inhibition (P < 0.05) of S. Typhimurium adhesion to and invasion of intestinal epithelial cells. Collectively, these findings support the potential of dietary apidaecin supplementation in poultry feed formulations to enhance intestinal health and improve the food safety of egg products by reducing Salmonella contamination.