OESTRUS, OVULATION AND FERTILITY FOLLOWING SUPPRESSION OF OVARIAN CYCLES IN MERINO EWES BY PROGESTERONE

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Abstract
Progesterone was administered to Merino ewes in February (early breeding season) and May (mid-breeding season) for 2 weeks. The period from the final progesterone injection to the onset of oestrus, the duration of oestrus, and fertility after hand mating were observed. The approximate time of ovulation was also determined in the February experiment. The duration of oestrus was 10 to 50 hr; ovulation took place near the end of oestrus. The period from the last injection to the onset of oestrus, and the fertility of the ewes were influenced by dose, interval between consecutive progesterone injections, the time of day that the injections were given, and the stage of the breeding season. Variability in onset of oestrus (indicating the degree of synchronization of oestrus) was least when the final injections were given in the morning. The results clearly show that normal levels of fertility may be achieved after synchronization of oestrus in Merino ewes with progesterone.