Short-term changes in serum luteinizing hormone, ovarian response and reproductive performance following gonadotrophin releasing hormone treatment in postpartum dairy cows with retained placenta.

Thirty-six postpartum Holstein cows consisting of eighteen cows that shed the placenta soon after calving (NRP) and eighteen cows that retained placenta greater than 24 h (RP) were used. There were four treatment groups. Group I consisted of 9 NRP cows which received intramuscular injection of sterile saline on day 15 postpartum. The second group consisted of 9 NRPN cows which received 100 micrograms of gonadotrophin releasing hormone on day 15 postpartum (NRPT). The third group consisted of 9 RP cows which received saline on day 15 postpartum (RPN) and the fourth group consisted of 9 RP cows which received 100 micrograms of gonadotrophin releasing hormone on day 15 postpartum (RPT). Blood samples were collected once daily during the first month and once every other day during the second month postpartum. In addition fourteen cows (RPT, n = 7; NRPT, n = 7), were used to study short-term changes in serum luteinizing hormone concentrations following gonadotrophin releasing hormone treatment on day 15 postpartum. Blood samples were obtained from these cows every 15 min during 1 h before and 6 h after gonadotrophin releasing hormone administration. Sera from all samples were assayed for progesterone and luteinizing hormone concentrations. Starting from four days after calving rectal palpations and ultrasound examinations of the ovaries were carried out once every four days until day 28 postpartum in order to monitor ovarian changes. All cows were inseminated on the first estrus after day 60 postpartum and examined for pregnancy between 35 and 42 days after insemination.(ABSTRACT TRUNCATED AT 250 WORDS)