The productivity of breeding ewes grazing on lucerne or grass and clover pastures on the tablelands of Southern Australia. 1. Reproduction

Abstract

The reproductive performance of Merino and Border Leicester x Merino ewes was measured over 3 years near Canberra. Ewes were stocked at six rates, from 9 to 18 ha-1, and lambed at two times (starting in mid-August or in early September) on pastures sown to subterranean clover and in which the main perennial species was either lucerne or phalaris. The effect of stocking rate on the proportion of ewes having multiple births was significant (P < O.05), and closely correlated to its effect on weight. The effect of stocking rate on the proportion of fertile ewes (i.e. ewes which were pregnant) was slight. Ewes grazing on lucerne were heavier at joining and gained more weight in the weeks before joining than did ewes on phalaris pastures. Although the proportion of fertile ewes was similar on both pastures, ewes grazing lucerne had fewer multiple births; this resulted in 8% fewer lambs per ewe joined in crossbreds and 9 % fewer in Merinos. The time of joining did not affect reproductive performance. Reproductive performance of both genotypes increased with the age of the ewes. There appeared to be year effects which were not related to weight or to weight gain at joining, although increases in reproductive performance with higher weight at joining were consistent from year to year.