Control of time of ovulation in heifers treated with progesterone and gonadotrophin releasing hormone

Abstract

The time of ovulation was determined in 29 heifers by laparoscopy following treatment with progesterone. In addition, 25 of the animals received 100 μg Gn RH 30 hr after the end of the progesterone treatment. Only 8 of the heifers treated with Gn RH ovulated. This contrasted with results obtained following examination of ovaries after slaughter in similar animals treated in identical fashion. Heifers which were treated with progesterone for 12 days and then slaughtered had not begun to ovulate 65 hr after the end of treatment, but 5 of 11 animals had ovulated 4 hr later. When Gn RH was given, ovulation had started 60 hr after the end of progesterone treatment, 60% of heifers had ovulated at 65 hr and 90% at 69 hr. Treatment with Gn RH can synchronize and hasten the time of ovulation in heifers given progesterone. Possible reasons for the discrepancy between the results obtained following laparoscopy and slaughter are discussed.