Estrogen — Induced release of luteinizing hormone in prepubertal and postpubertal heifers

This experiment was designed to determine the age at which estradiol-17β (E 2) first induces a preovulatory-like surge of luteinizing hormone (LH) in prepubertal heifers. Responses of prepubertal animals 3 to 4 and 5 to 6 months of age were compared with those of postpubertal heifers that received 25 mg prostaglandin F 2α at 0800 hr on day 15 of the estrous cycle. E 2 (500μg) induced surges of LH in 1 5 heifers 3 to 4 months of age, 3 3 heifers 5 to 6 months of age and 5 5 postpubertal heifers. Duration of response and interval between E 2 injection and peak of the response were longer in postpubertal heifers than in those 5 to 6 months old (P