Assessment of reproductive wastage in sheep. 3. An investigation of a commercial sheep flock

Abstract

Infertility in a sheep flock in the Moree district of New South Wales was investigated during 1973. Detailed observations were made in two sub flocks and data were obtained in both maiden and adult ewes for proportion of ewes mating, ovulation rate, fertilization rate, and number of foetuses at 60 days of pregnancy. These estimates were used to apportion prenatal wastage to mating failure, fertilization failure or early embryonic mortality. Ovulation rate in the flock was high (1.27 maiden ewes, 1.73 adult ewes) and fertility low with 83 per cent of maiden ewes and 27 per cent of adult ewes not pregnant when examined by laparotomy 60 days after mating. In the adult ewes this infertility was accounted for by failure to mate (30 per cent of dry ewes) and early embryonic mortality (70 per cent of dry ewes). In the maiden ewes, failure to mate accounted for 34 per cent, embryonic mortality 52 per cent and failure of fertilization 14 per cent of the dry ewes. The problems of estimation and interpretation involved in this type of investigation are discussed.