Effect of zinc supplementation on the reproductive performance of grazing Merino ewes

Two experiments were carried out in Western Australia to investigate the effect of zinc supplementation, on the reproductive performance of grazing Merino ewes. We found that supplemental zinc, when provided prior to mating and throughout pregnancy, increased the number of lambs produced by 14% (P<0.05) in both experiments. An intermediate zinc treatment, when supplementation was begun later in pregnancy gave a 9% (P<0.01) increase in the number of lambs in one experiment and no increase in the second. Lamb birth weights were increased by zinc supplementation in Experiment 1 and in Experiment 2, 12–20-week-old lambs from zinc supplemented ewes were 2.1 kg heavier than those from nonsupplemented controls. Plasma zince levels decreased significantly during pregnancy and lactation, but were increased at some sampling dates by 20–25% by zinc supplementation.