Seasonality of ovulation and estrus in Border Leicester ewes

Abstract

The number of Border Leicester ewes ovulating and their ovulation rate at 4 to 6 week intervals over 1 year and again after a further year were determined. The proportion of these ewes expressing estrus from autumn to spring and then in late summer/autumn was also determined. None of the ewes ovulated from October to early February, but for the remainder of the year, ovulation rate was always above 1.60, peaking in April to June at over 2.0. Eighty-four percent of the ewes had commenced ovulating by early March. The breeding season continued to September, when 10% of the ewes ovulated, with 25% expressing estrus in August and September. There was no significant effect of age, ewe liveweight or liveweight change on the proportion of ewes ovulating and their ovulation rate. The variability in the length of the breeding season gives scope for further selection.