THE PRODUCTION OF COINCIDENT OESTRUS AND OVULATION IN THE ANOESTROUS EWE WITH PROGESTERONE AND PREGNANT MARE SERUM

Abstract

SUMMARY 1. Sixty crossbred maiden ewes, twelve of which were hysterectomized, and eighteen mature ewes were used during the non-breeding season in two experiments involving injection with 75 mg of progesterone intramuscularly and 1000 i.u. of pregnant mare serum (PMS) subcutaneously, either alone or in combination. 2. Progesterone given as two daily injections of 12·5 mg each for 3 days, followed 2 days later by 1000 i.u. of PMS resulted in oestrus with ovulation in sixteen out of eighteen ewes treated. The two remaining ewes failed to ovulate owing to the presence of active corpora lutea. 3. Three injections of 25 mg progesterone/day, or a single injection of 75 mg progesterone followed by PMS, were decreasingly less effective in inducing oestrus. 4. Progesterone alone in the form of two daily injections of 12·5 mg for 3 days without subsequent PMS, was followed by ovulation in five out of six mature ewes, three of them exhibiting oestrus and producing lambs subsequently. 5. Time relationships were physiologically normal, oestrus commencing 24 to 36 hr after PMS and preceding ovulation by 10–20 hr. The ovaries showed no histological abnormalities. 6. Hysterectomized and intact ewes responded alike, suggesting that the conditioning effect of progesterone is a central phenomenon.