Survey observation on the mating performance of sheep in New Zealand Romney stud flocks

Abstract

The mating performance of 2075 New Zealand Romney rams joined singly with 127,683 ewes for three 16-day periods during the breeding season is given. These observations were conducted between 1962 and 1969 in stud flocks situated in four geographical localities based on latitude, throughout New Zealand. Area differences were observed in mean dates of first joining, in the number of ewes in oestrus, and in conception and return rates. Rams were joined with the ewes later in southern areas. When compared with flocks in the North Island, southern flocks showed a higher proportion of ewes detected in oestrus during the first 16 days of mating, higher conception rates, and lower return rates. Wide differences were observed between rams as regards the conception rate of ewes. Significant correlations between numbers of ewes joined and proportions of ewes detected in oestrus showed a quadratic rather than a linear fit, with marked differences from north to south. There were no significant correlations between the number of ewes joined and percentage conception rate.