Effects of dietary Bacillus subtilis on heat-stressed broilers performance, intestinal morphology and microflora composition

The aim of this study was to investigate the effect of dietary inclusion of Bacillus subtilis on performance, thermotolerance, intestinal villus-crypt system, and intestinal microflora balance of broilers subjected to heat stress. Four hundred eighty 1-d-old Hubbard male broilers were randomly distributed into 4 treatment groups, with 6 replicates per treatment and 20 birds per replicate. A 2 × 2 factorial arrangement was used; the main factors were environmental temperature (thermoneutral or heat stress) and diet (basal diet or basal diet + 1 g/kg B. subtilis). From d 21 to 35, birds were either exposed to thermoneutral conditions (21 °C: throughout the experiment) or intermittent heat stress (35 °C from 09:00 to 14:00 and 21 °C from 14:00 to 09:00). Compared to B. subtilis supplemented groups, birds subjected to heat stress and fed the basal diet had reduced (P<0.05) final body weight, daily gain, feed intake, duodenal and ileal villus height, crypt depth, villus surface area, absorptive epithelial cell area and viable counts of Lactobacillus and Bifidobacterium. Dietary inclusion of B. subtilis reversed (P<0.05) the previous reductions and decreased (P<0.05) feed to gain ratio, mortality and viable counts of Clostridium and Coliforms. B. subtilis had extra positive effects in heat-stressed broilers as revealed by significant temperature × diet interactions detected in final body weight, average daily gain, villus height, villus surface area, absorptive epithelial cell area and beneficial intestinal bacteria counts. Birds' thermotolerance was not improved (P>0.05) by dietary inclusion of B. subtilis. It is concluded that inclusion of B. subtilis in the diet of heat-stressed broilers was partially effective in overcoming the adverse effects on performance by restoring the impaired villus-crypt structure and enhancing the colonization of beneficial intestinal bacteria.