Abstract: This study was conducted for comparison the effect of some feed growth promoter additives on performance and gut microflora population of 21 days old broiler chickens. Based on randomized completely design, 300 days old Ross 308 broilers were distributed into 30 floor pens and reared for 21 days. The basal diet was also supplemented with Flavomycin, Primalac, Biolex-MB and mixture of Primalac plus Biolex-MB, resulting 5 dietary treatments were prepared including control group. Each dietary treatment was fed ad-libitum to 6 replicate group of 10 bird at the bigining of rearing period. The result of experiment indicate that diets containing growth promoters improved broilers performance. This improvement was only significant (p<0.05) between control group and both Biolex-MB and synbiotic treatment groups, for body weight gain and between control group and 3 bird groups fed Flavomycin, Biolex-MB and synbiotic dietary treatments for feed conversion raito. Compared with control birds group, all other treatment groups fed growth promoter diets had relatively lower total bacterial population in crop except for Primalac treatment, but this differences was significant (p<0.05) only between Flavomycin and control group treatments. Birds fed diets containing growth promoter had greater lactic acid bacteria populations in crop compared with control group, but this priority was significant (p<0.05) only for synbiotic group. A reversed trend were found for coliforms population in ileum, where all growth promoter groups, except Flavomycin, had significantly (p<0.05) lower population compared with control group. Additionally, such feed additives altered the pH content of crop and ileum.
N. Dabiri, A. Ashayerizadeh, O. Ashayerizadeh, K.H. Mirzadeh, H. Roshanfekr, M. Bojarpour and M.R. Ghorbani, 2009. Comparison Effects of Several Growth Stimulating Additives on Performance Responses and Microbial Population in Crop and Ileum of Broiler Chickens on Their 21st Day of Life. Journal of Animal and Veterinary Advances, 8: 1509-1515.