Three broiler trials were conducted to age of 7-days, 21-days and 42-days, for trials I, 2, and 3, respectively. In trial 1, two treatments were used: 1) the control (c) in which chicks received no preventive medication in the form of chlortetracycline (tetracycline HCL); 2) preventive medication (m-7) in which one day old chicks were given a preventive course (for seven days) of chlortetracycline at 0.5 g/L drinking water. In trial 2, three treatments were used: treatments 1 (c) and 2 (m-7) where similar to those in trial 1; however, chicks in treatment 3 (m-10) were given the preventive course for 10 days. In the third trial, four treatments were used, 1) common broiler house clean-out and chicks were given no medication (c-nm); 2)

common broiler house clean-out and one day-old chicks were given a preventive