The influence of injected progesterone and oestradiol on ovarian and uterine response to injected pms was studied in seventy-nine mature white-faced ewes.The percentage of ewes ovulating (by treatment groups) were: control (no treatment), 100; 8 mg progesterone daily, 20; 16 mg progesterone daily, 0; 1200 i.u. pms on Day 14, 78; 8 mg progesterone daily + pms, 80; 16 mg progesterone daily + pms, 10; 16 mg progesterone + 10 mg oestradiol, 10; 16 mg progesterone + pms + oestradiol, 80. Average follicular fluid weights were statistically higher in the groups receiving 8 and 16 mg progesterone + pms and tended to be lower in groups receiving either 16 mg progesterone alone or 16 mg progesterone + oestradiol. The incidence of cystic and/or luteinized follicles was low.
Average uterine weight was significantly higher in the groups receiving pms alone (91 ·3 g) and significantly lower in the groups receiving 8 or 16 mg progesterone alone (53·4 and 44·1 g) than the uninjected controls (74·3 g). The remaining groups were very similar to the uninjected controls but showed greater weight response when compared to appropriate progesterone controls than the group receiving pms alone. The incidence of oestrus was closely associated with the incidence of ovulation except it was less frequent in groups receiving progesterone. The low incidence of ovulation in progesterone modified ewes treated with oestradiol alone, and pms alone, compared to the high incidence when these two hormones were given together indicates a gonadalgonadotrophic hormone interaction, probably at the level of the ovaries.