Hormonal and reproductive profiles of early postpartum beef heifers after prolactin suppression or steroid-induced luteal function.

Two trials were conducted with 24 primiparous suckled beef heifers to determine independent and combined effects of a prolactin-suppressing agent and exogenous steroids on serum hormones and reproductive activity. Heifers were assigned in groups of six to one of four treatments: 1. (C)subcutaneous control injections administered once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpartum or until first naturally occurring estrus; 2. (CB)subcutaneous injections of 80 mg CB-154 (2-bromo-~-ergokryptine) (Sandoz) in ethanol once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpar tum or unti l first naturally occurring estrus; 3. (PE)intramuscular (IM) injection of 25 mg progesterone in sesame oil on day 15 postpartum, followed by IM injection of 4 mg estradiol-17 in sesame oil 48 hr later, or 4. (CBPE)-treatments 2 (CB) plus 3 (PE). A marked reduction in serum prolactin was observed after a single injection CB-154 in all CB and CBPE treated heifers, reaching minimum concentrations by day 7