Ovulatory activity in mature romney ewes in Otago

Abstract

Ovulatory activity in 5–7 yr Romney ewes in Otago followed identical patterns in 1957 and 1958. First seasonal ovulations had occurred in less than 10% of ewes by the end of February, in 50% of ewes by 19 March, and in all normal ewes by mid April. Cyclic ovulation continued between mid April and late August but throughout September an increasing proportion of ewes ceased to ovulate. Fifty per cent had ceased seasonal activity by 11 September. In October and November, sporadic non-cyclic ovulations occurred in 2–8% of the ewes examined. The mean number of ovulations per ewe varied significantly depending on the stage of the season at which ewes were examined, and reached a peak value of 1.83 ovulations per ewe in April. These observations are discussed in relation to ewe fertility.