Response of Anestrous Does and Ewes to Pregnant Mare's Serum during Two Consecutive Seasons

Abstract

Erratic results were obtained in two similar experiments conducted in 1942 and 1943 in which the action of pregnant mare serum (PMS) was studied in connection with the induction of estrus in does and estrus accompanied by ovulation in ewes during their anestrous seasons. During the 1942 season 19 out of 20 does (95 percent) came in estrus following one or more injections of PMS, whereas during the 1943 season 6 out of 56 (11 percent) exhibited estrus following comparable treatment. In 1942, 6 out of 14 ewes that were given PMS came in estrus and all had ovulated when examined by laparotomy. Following comparable dosages of PMS in 1943, only 2 out of 26 came in estrus and 9 out of 25 had ovulated when examined. Attention is called to the possibility that environmental or nutritional variables are involved in the divergent responses often exhibited by ewes and does to the administration of PMS. Copyright © . .