Abstract LIMITED information is available on the effects of tetracycline antibiotics on the performance of turkey breeder hens. Several reports related to the use of antibiotics in the feeds of commercial laying hens and heavy chicken breeders have been published during the past few years (Carlson, 1959; Heywang, 1959; O’Neal and Savage, 1959; Ryan et al., 1961; Eoff et al., 1962). In general, these reports have shown improvements in egg production and feed efficiency due to the feeding of antibiotics. White-Stevens et al. (1955) reported that the continuous feeding of 100 to 200 grams of chlortetracycline per ton of feed to Beltsville Small White turkey breeders significantly increased eggs per hen housed and poults hatched per hen housed. With turkey breeder hens exhibiting a fertility problem, Green et al. (1963) observed in two experiments that tetracycline antibiotics administered through the feed or by injection prevented the precipitous drop in fertility observed …