The Influence of Time of Lambing on the Performance of Fine Wool Merino Ewes

Observations were carried out at Lismore in western Victoria on the performance of two groups of 250 fine wool Merino ewes mated in spring (November) and autumn (May) respectively. A greater proportion of ewes lambing in spring lambed within 150-170 days after the introduction of the rams than ewes lambing in autumn. The duration of lambing was shorter in spring. There were no significant differences in the proportion of ewes lambing, in the proportion of twins born or in the proportion of lambs marked between the two groups. Ewes lambing in spring weaned more lambs than ewes lambing in autumn because of a higher lamb survival rate in the spring (spring = 90%, autumn = 81%). The lambs born in spring were heavier at birth (P < 0.001) and grew faster than the lambs born in autumn. Body weights at 18 months of both groups were variable; at 30 months of age, both groups had body weights of approximately 36 kg (80 lb).