Seasonal variation in the ovarian activity of Merino ewes

Abstract

Ovulation was studied in a flock of medium Peppin Merino ewes known to show little seasonal variation in the incidence of twin births. In the absence of rams, ovarian activity was lowest in the spring and highest in the autumn, but the proportion of twin ovulations did not vary significantly from a constant level throughout the year. The incidence of twin ovulations, following an advanced onset of the breeding season, initiated by the sudden introduction of rams in the early summer, did not differ from that occurring during the 'natural' breeding season.