Evaluation of the efficacy of chlortetracycline for the control of chronic respiratory disease caused by Escherichia coli and Mycoplasma gallisepticum.

Using different variations of challenge, three trials were conducted to evaluate the efficacy of chlortetracycline in the control of chronic respiratory disease (CRD) caused by Escherichia coli and Mycoplasma gallisepticum. Experimentally infected birds were offered either food containing chlortetracycline at 300 ppm or water containing the drug at 120 mg litre-1. In each trial, medicated food and water were effective in the control of CRD as assessed by reduction in clinical signs, lower mortality and reduced severity of air sacculitis and other post mortem lesions. Weight gain was also improved by both forms of medication. M gallisepticum antibodies were demonstrated in surviving birds.