Effects of probiotic (Bacillus subtilis DSM 17299) supplementation on the caecal microflora and performance in broiler chickens

The aim of the study was to determine the effects of dietary probiotic supplementation with B. subtilis spores (strain DSM 17299) on the growth performance and carcass traits in broiler chickens and to analyse the influence on the caecal microflora. A total of 364 one day-old male broiler chicks were randomly divided into 2 equal groups (not supplemented controls and birds receiving dietary addition of B. subtilis spores (8x10(5) cfu/kg of food) for 6 weeks). Body weights, body weight gains, food intake and food efficiency were weekly evaluated and the carcass parameters (hot carcass weight and yield) and the caecal microflora composition were determined at the end of the experiment. The probiotic supplementation has significantly increased the final weight gain (P < 0.05) and the hot carcass weight (P < 0.01), reduced the food intake calculated for 6 weeks (P < 0.001) and improved the food conversion ratios since the 4th week with supplementation (p < 0.001). In parallel, in the treated birds, the caecal population of bacilli was markedly enhanced (P < 0.01) whereas those of enterococci (P < 0.001) and coliforms (P < 0.05) were significantly lowered. The Enterobacteriaceae counts were also weakly depressed but not significantly and the numeration of lactobacilli has also tended to slightly increase. These results show that the dietary inclusion of B. subtilis spores improve the weight growth and the food efficiency in broilers probably through the selection of beneficial bacteria to the detriment of pathogen germs in the caecal microflora.