Effects of Antibiotics on Growth Performance, Immune Response, and Intestinal Microflora of Broilers

Abstract

This study was conducted to evaluate the effects of flavomycin, lincomycin, and zinc bacitracin on body growth, morphometery of immune organs, Newcastle disease virus (NDV) and avian influenza virus (AIV) antibody response, intestinal microflora, and feed efficiency of broilers. Forty-five day-old broiler chickens were randomly divided into five treatments and housed under identical husbandry conditions. Antibiotic-free poultry feed was procured from a commercial feed mill. The antibiotics were mixed in the feed as per the manufacturer's instructions and offered ad libitum to the chickens for the entire study period. The chickens were vaccinated for NDV and AIV. None of the antibiotics adversely affected the development of NDV or AIV hemagglutination inhibition geometric mean titers. Flavomycin and zinc bacitracin did not adversely affect the mean splenic (1.27+0.20 g and 1.21+0.15 g, respectively), thymic (3.42+0.26 g and 3.78+0.48 g, respectively), hepatic (21.78+0.83 g and 23.15+0.37 g, respectively), or bursal (1.55+0.79 g and 1.63+0.21 g, respectively) body weight ratios. However, lincomycin did adversely affect bursal (0.91+0.12 g), but not splenic (1.21+0.23 g), thymic (3.52+0.36 g), or hepatic (23.72+1.78 g) body weight ratios. The total viable bacterial counts per gram of feces before and 120 h after medication were significantly different (p<0.05). Interestingly, the feed efficiency of non-medicated, non-vaccinated chickens was equal to the flavomycin-medicated chickens but better than zinc bacitracin and lincomycinmedicated chickens. Additionally, the non-medicated, non-vaccinated chickens were the most economical to raise. Overall growth-promoting antibiotics did not interfere with the broiler's immunity, altered total intestinal microflora counts, or improved feed efficiency.