Investigation of Intestinal Microflora of Young Broilers and Their Growth Response to Feed Supplemented with Roxarsone, Avilamycin and Formycin Gold

‏ This experiment was conducted to determine the performance and intestinal microflora population of broiler chicks in diets supplemented with Roxarsone, Avilamycin and Formycin gold during starter period. A basal diet was formulated according to NRC (1994) recommendation for starter (0-21 d) period and also supplemented with appropriate amounts of the mentioned growth promoters. Each of the treatment was fed to 5 replicates of 18 Ross 308 male broilers. The birds were raised on pen floor for 21 days. The microflora population in crop and ileum parts was measured on appropriate bacteriological media. Results of experiment indicated that supplementation of Roxarsone and Avilamycin, especially their combination to broiler diets, significantly improved body weigh gain of birds (P<0.05). Feed consumption and feed conversion ratios were not affected by any of the mentioned growth promoters. Adding all the growth promoters to the basal diet, except for the treatment of 0.05 percent Formycin gold, decreased total bacterial numbers in crop and ileum parts. Broilers fed diets containing Roxarsone plus Avilamycin had the lowest total bacterial population and were significantly different from those fed the basal diet (P<0.05). Supplementing broiler diets with all the growth promoters increased lactic acid bacteria population in crop, and decreased coliforms population in ileum parts. Lactic acid bacteria population was the highest in broilers fed Roxarsone plus Avilamycin and coliforms population was the lowest in birds fed 0.2 percent Formycin gold, being significantly different from basal diet (P<0.05).