Effects of variation in liveweight at birth and weaning on subsequent reproductive rate in sheep

Observations were carried out on one Polwarth, three Corriedale, and four Merino flocks in Western Victoria to investigate the influence of a ewe's own live weight at birth and weaning on her subsequent reproductive performance, when lambing for the first time. Weaning weights were adjusted to 140 days of age. The mean adjusted weaning weights were 26-35 lb (Merino), 27-48 lb (Corriedale), and 37 lb (Polwarth). Variation in the live weight of ewes at birth had little or no effect on either the number of lambs born per ewe joined (LBJ) or the number of lambs weaned per ewe joined (LW]), when the ewes lambed for the first time at either two or three years old. Variation in the live weight of ewes at weaning generally had only a small effect on both LBJ and LWJ at first lambing. On three properties, there was, however, an increase of about 3 per cent in LBJ and about 2 per cent in LWJ for each 10 lb increase in the ewe's own live weight at weaning.