Oestrus and ovulation following administration of placental gonadotrophins to Merino ewes

Abstract

Following progesterone suppression of ovarian cycles, Merino ewes were given a combination of pregnant mare serum gonadotrophin (PMS) and human chorionic gonadotrophin (HCG) 1 or 2 days after the final injection of progesterone. The incidence of oestrus was recorded and the ewes were mated with entire rams. Laparotomy was carried out 2–3 days after oestrus to observe the number of ovulations and the follicular changes. The ewes were killed 5–6 weeks after treatment and conceptions noted. In non-pregnant ewes the incidence of cystic hyperplasia of the endometrium was recorded. The results may be summarized as follows:(a) Oestrus was inhibited in a high proportion of ewes receiving doses of 540 or 1620 i.u. of HCG. This was independent of the dose of PMS. (b) The number of large follicles was greatest at high doses of HCG. (c) In ewes receiving high doses of HCG, oestrus, if it occurred, was associated with large follicles. (d) Less than 10% of ewes conceived. (e) Endometrial cysts were present in a high proportion of ewes. It is suggested that HCG has a dual effect on ovarian function, depending on dose and the time of injection in relation to stage of follicular growth.