REPRODUCTIVE-PERFORMANCE IN HIGH PRODUCING DAIRY-COWS TREATED WITH RECOMBINANT BOVINE SOMATOTROPIN

The reproductive performance of 156 cows treated with recombinant bST for two consecutive lactations was assessed as part of a target animal safety study conducted in the San Joaquin Valley of central Californi a. Daily intramuscular administration of 17.2, 51.6, and 86 mg of bST per cow started at d 70 postpartum and ended at dry-off or 305 d postp artum. The Al did not begin until d 70 postpartum. During the first la ctation study, multiparous cows treated with bST had significantly dec reased pregnancy rates, increased behavioral anestrus, and increased a nestrus confirmed by palpation. Treated primiparous cows in first lact ation had shorter mean days to first standing estrus. In the second la ctation study, cows treated with bST had an increased rate of delayed uterine involution, cystic ovarian condition, behavioral anestrus, and anestrus confirmed by palpation. Progeny from the first lactation cow s were evaluated for rates of growth, morbidity, mortality, and for re productive performance; no difference was detected between the progeny from different groups.