Effects of progesterone and Pregnant Mare Serum (PMS) adminsitration in the anoestrous ewe. I. Oestrus, ovarian changes, and gonadotrophic potency of the pituitary gland

Abstract

Observations were made on the effect of progesterone and pregnant mare serum (PMS) on the incidence of oestrus, the macroscopic changes in the ovaries, and the total content of gonadotrophins in each anterior pituitary gland of 105 anoestrous Romney ewes. When progesterone alone was administered for 4 days neither oestrus nor ovulation resulted. In the group receiving PMS alone, ovulation occurred in 6 of 10 ewes but none exhibited oestrus. All 10 ewes injected with both hormones ovulated; only 6 came on heat. No effect of progesterone or PMS on pituitary activity was apparent when the animals were killed 4-7 days after the last injection of hormone. Some evidence for an increase in numbers of small follicles over an 8-day period in January suggested perhaps a natural increase in ovarian activity with the approach of the normal breeding season, or a stimulatory effect of the introduction of the rams a t that time of year. Over the same period the gonadotrophic potency of the control sheep showed a slight increase. These observations are discussed in the light of current views of pituitary control of the breeding season in sheep.