The occurrence of oestrus in ewes and the duration and detection of pregnancy in artificially inseminated ewes

Abstract

In a flock of 256 Corriedale ewes at Mittagong, New South Wales, the mean length of the oestrous cycle in two successive years was 16.9 ± 1.14 days, and the length of gestation was 150.7 ± 2.28 days (mean ± S.D.). The proportion of ewes observed in oestrus during two periods of the day is also reported. In these trials and in subsequent insemination trials (two with Corriedale ewes at Mittagong and one with Merino ewes at Mudgee) more ewes commenced oestrus per hour between 7.30 a.m. and 6.00 p.m. than during the remainder of the 24 hours. Returns to oestrus within 24 days of insemination, or scores of udder development 160 days after the last day of insemination, provided as good an index of the pregnancy rate as mothering lambs at birth.