Effect of a probiotic mixture on intestinal microflora, morphology, and barrier integrity of broilers subjected to heat stress

The current study investigated the efficacy of a probiotic mixture on ameliorating heat stress-induced impairment of intestinal microflora, morphology, and barrier integrity in broilers. The probiotic mixture contained Bacillus licheniformis, Bacillus subtilis, and Lactobacillus plantarum. Three hundred sixty 21-d-old Ross 308 male broilers were allocated in 4 experimental treatments, each of which was replicated 6 times with 15 broilers per replicate. A 2 × 2 factorial design was used in the study, and the main factors were composed of diet (basal diet or addition of 1.5 g/kg of probiotic mixture) and temperature (thermoneutral zone or heat stress). From d 22 to 42, birds were either raised in a thermoneutral zone (22°C) or subjected to cyclic heat stress by exposing them to 33°C for 10 h (from 0800 to 1800) and 22°C from 1800 to 0800. Compared with birds kept in the thermoneutral zone, birds subjected to heat stress had reduced ADG and ADFI; lower viable counts of Lactobacillus and Bifidobacterium and increased viable counts of coliforms and Clostridium in small intestinal contents; shorter jejunal villus height, deeper crypt depth, and lower ratio of villus height to crypt depth; decreased jejunal transepithelial electrical resistance and a higher level of jejunal paracellular permeability of fluorescein isothiocyanate dextran 4 kDa; and downregulated protein levels of occludin and zonula occludens-1 (P < 0.05). Supplemental probiotics increased (P < 0.05) small intestinal Lactobacillus and Bifidobacterium, jejunal villus height, protein level of occludin, and decreased (P < 0.05) feed to gain ratio and small intestinal coliforms. These results indicate that dietary addition of probiotic mixture was effective in partially ameliorating intestinal barrier function. But no temperature × diet interaction was observed in the present study, revealing that the supplemented probiotics had the same effect at both temperatures.