QUANTITATIVE STUDIES OF THE INTERACTION BETWEEN PROGESTERONE AND PREGNANT MARE SERUM ON OVARIAN FUNCTION IN THE EWE

Injections of progesterone were given to ewes to suppress ovarian cycles; pregnant mare serum gonadotrophin (pms) was administered within 2 days of the final injection of progesterone. Oestrus, numbers of ovulations and follicle growth were observed during the week following treatment. In some experiments, ewes were mated to fertile rams and fertility and fecundity were recorded. Experiments were carried out at different stages of the breeding season. Relationships between methods of suppression of ovarian cycles (dose and frequency of injections of progesterone) and methods of ovarian stimulation (dose and time of administration of pms in relation to the final progesterone injection) for each of the responses were examined. The most important finding was that for comparable dosage levels of pms, the numbers of ovulations were greater after progesterone injections on alternate days than after daily injections. Stage of the breeding season and introduction of rams influenced the results.