Studies in ovine fertility in agricultural regions of Western Australia : ovulation rate, fertility and lambing performance

Abstract

A total of 29,500 ewes, of which 2049 were laparotomized, in 53 flocks were used to determine the extent by which variations in body weight and age of the ewes and the temperature and day length about the time of mating were associated with the number of ovulations per 100 ewes (ovulation rate) and reproductive performance of sheep in south Western Australia. Overall there were only 113.7?2.2 ovulations per 100 ewes in the flocks studied. Less than 3% of the ewes failed to ovulate, so that in general differences between flocks were due to differences in the rate of multiple ovulation. Flocks with high ovulation rates produced more lambs per 100 ewes. There were about six extra lambs per 100 ewes for every 10% increase in the ovulation rate. About 40% of these extra lambs were due to extra twins; the remainder were due to more ewes lambing. Both age and body weight of the ewes were significantly correlated with ovulation rate (r = 0.41, P < 0.01 and r = 0.42, P < 0.01, respectively) and all the parameters of reproduction studied. Each 5 kg difference in body weight was associated with 5.9 extra ovulations per 100 ewes (P < 0.01).