Effect of dietary antibiotics on chickens infected with Eimeria tenella

Two experiments were performed to study the effect of dietary antibiotics on percent daily weight change, mortality and gross cecal pathology in chickens during the critical phase of Eimeria tenella infection. In the first experiment, chickens were continuously fed ration containing thiopeptin, 2 mg/kg.; bacitracin, 20 mg./kg.; penicillin, 12 mg./kg.; or chlortetracycline, 22 mg./kg. One day after antibiotic fed was given, each bird received an oral inoculation of 30,000 sporulated oocyts. In the second experiment, chickens were consecutively fed ration containing amprolium plus ethopabate, 125 plus 8 mg./kg., and a combination of the coccidiostat and one of 4 antibiotics; thiopeptin, bacitracin, penicillin, or chloretracycline. One day after medicated feed was given, birds were each given an oral inoculation of 30,000 amprolium plus ethopabate-resistant E. tenella oocysts. The experiments were terminated 7 days after coccidia exposure. In both experiments, E. tenella infection resulted in depression in all birds of infected groups. Average percent weight change of infected birds was significantly lower than that of uninfected unmedicated control between 4 and 5 days after infection. Significantly greater number of birds died of cecal coccidiosis in group fed dietary bacitracin than that of other infected groups. Dietary antibiotics did not reduce gross cecal lesions.