The effect of season on the ovulation rates of Merino and crossbreed ewes in Western Australia

Abstract

Five experiments involving Merino and Border Leicester X Merino crossbred ewes were carried out to investigate the effect of season on ovulation and ovulation rate in the Western Australian agricultural areas. In one experiment, involving Murray Merinos only, effects of body weight and of introduction of teaser rams were also investigated. In 1966 the breeding season began in January for Murray Merinos, but in 1966-67 some ewes had already ovulated in December. Introduction of teaser rams in early December made teased ewes ovulate sooner than unteased ewes. The number of ovulations per ewe ovulating increased during the breeding season, reaching peaks of 1.8 eggs per ewe ovulating in April and early May 1966, and 1.6 eggs per ewe ovulating in February 1967. Supplementary feeding hastened the onset of the breeding season and tended to increase ovulation rate. Peppin Merinos showed a low incidence of ovulation, which was ascribed to their very poor body condition. The Border Leicester X Merino crossbred ewes began their breeding season in March in one experiment, but more than half the ewes had already ovulated in December in the other experiment, perhaps because they were much heavier. Both group's showed marked increases in ovulation rate as their breeding seasons progressed.