EFFECT OF PREMATING NUTRITION ON REPRODUCTIVE-PERFORMANCE OF BOOROOLA MERINO X SOUTH AUSTRALIAN MERINO EWES

To investigate the effect of pre-mating nutritional status on the reproductive performance of ewes carrying the Booroola (Fec(B)) gene, Booroola Merino x South Australian Merino ewes heterozygous for the high fecundity gene (Fec(B) Fec+), were exposed to varying levels of nutrition 11 weeks before and 6 weeks during mating, and the reproductive performance and productivity were assessed. Liveweight varied from 44.0 to 55.2 kg for five nutritional treatments and mean ovulation rates varied from 2.62 to 3.01. The positive response of ovulation rate to improved nutrition was reflected in increases in litter size at days 40 and 80 of pregnancy, and at birth (P < 0.05). There were no statistically significant differences between nutritional treatments for either the proportion of pregnant ewes of ewes mated or lamb survival. Differences between nutritional treatments for ovulation rate and litter size were not reflected in net reproductive efficiency (lambs weaned per ewe exposed). Lamb growth was not affected by varying the level of pre-mating nutrition of the ewe, although ewe fleece weight and wool quality (tenderness) were compromised.