Effect of probiotic supplementation on the expression of tight junction proteins, innate immunity-associated genes, and microbiota composition of broilers subjected to cyclic heat stress.

This study investigated the effects of probiotic on intestinal innate immunity-associated gene expression and cecal microbiota in heat-stressed broilers. A total of 180 21-day-old male broilers were randomly assigned to three treatment groups with four replicates per group. The thermoneutral group (TN) (23 ± 1°C) received a basal diet, and another two heat-stressed groups (28-35-28°C for 12 h daily) were fed the basal diet (HS) or the basal diet supplemented with probiotic at a dose of 1.5 × 10  CFU/kg (HS_Pro) for 21 consecutive days. Compared with the TN group, the abundance of beneficial bacteria was decreased (p < 0.05) in the caecum of heat-stressed broilers. Heat stress downregulated (p < 0.05) the expression of Toll-like receptor (TLR)2 and upregulated (p < 0.05) the expressions of TLR5, TLR15, avian β-defensin (AvBD)4, AvBD8, and AvBD14 in the ileum as compared with the TN group. Dietary supplementation of probiotic upregulated (p < 0.05) the occludin expression in the ileum, improved the microbiota balance in the caecum, and decreased (p < 0.05) the gene expressions of TLR5 and TLR15 in the ileum of heat-stressed broilers. Collectively, dietary probiotic supplementation could promote intestinal barrier function via improving gut microbiota community and regulating innate immunity-associated gene expressions in heat-stressed broilers.