Effect of zinc bacitracin and salinomycin on intestinal microflora and performance of broilers

A feeding experiment was carried out over 42 d with four groups of broiler chickens fed experimental diets formulated to provide no supplementation, 2 0 mg zinc bacitracin, 60 mg salinomycin, or both feed additives in combinat ion. During the fifth week of the experiment, four chickens from each pen w ere killed, and the contents of gizzard, duodenum, jejunum, ileum, ceca, an d rectum were separately collected and pooled. In all intestinal segments, the pH and the concentration of lactic acid were measured, and the numbers of anaerobic bacteria, coliforms, lactic acid bacteria, lactobacilli, enter ococci, and Clostridium perfringens were counted. In homogenates of pancrea s obtained from four animals, the activities of amylase, lipase, trypsin, a nd chymotrypsin were measured. A significant growth-promoting effect was observed in the group receiving z inc bacitracin in combination with salinomycin. Zinc bacitracin significant ly reduced the number of coliform bacteria in the ileum and increased the a ctivities of amylase and lipase in pancreas homogenates. Supplementation with salinomycin and zinc bacitracin, alone or in combinati on, resulted in significantly lower counts of C. perfringens as well as Lac tobacillus salivarius, which was a dominant lactic acid bacterium found in broiler intestinal contents. High numbers of these lactobacilli may play a role in broiler growth depression related to competition in nutrient uptake or impaired fat absorption due to bile acid deconjugation.