The ovarian response to pregnant mare serum (PMS) administered after intravaginal progestagen treatment of cyclic and anoestrous ewes

PMS was administered at several dose levels (250, 500, 750, 1000, and 1250 nominal i.u.) to progestagen-treated cyclic and anoestrous ewes. Times of PMS administration were 24 hr prior to and at the time of removal of the intravaginal pessary. The time of administration of PMS significantly affected oestrous response and the time of onset of oestrus. The stage of the breeding season also affected the time of onset of oestrus. The number of ovulations, as measured by the number of corpora lutea, was affected by the stage of the breeding season and dose of PMS. The anoestrous ewes had a greater number of ovulations than the cyclic ewes, particularly al the higher dose levels of PMS.