Effect of Breeding Heavier Romney Ewe Lambs at Seven Months of Age on Lamb Production and Efficiency over Their First Three Breeding Seasons

SIMPLE SUMMARY: This experiment examined the impact of breeding heavier ewe lambs on lamb production and the ability of a ewe to produce a high number and heavier lambs (i.e., efficiency) over the first three breeding seasons. Two groups of ewe lambs were bred at seven months of age at an average live weight of either 47.9 ± 0.36 kg (n = 135) or 44.9 ± 0.49 kg (n = 135). Ewe live weight, number of lambs born and weaned, and lamb live weights were recorded, and ewe efficiency was calculated for each ewe. The weight and number of lambs at weaning over the three-year period did not differ between treatments, however, when data were pooled, heavier ewe lambs at breeding had a greater number and lamb weaning weight over the three-year period. Breeding heavier ewe lambs had no effect on ewe efficiency. There was a positive relationship between ewe lamb breeding live weight and their mature weight. These results suggest that breeding heavier ewe lambs increased the total lamb production over the three-year period, however, it had no effect on ewe efficiency. Before final recommendations can be made, ewe lifetime performance and longevity of heavier ewe lambs at breeding are required. ABSTRACT: This experiment examined the effect of breeding heavier ewe lambs on lamb production and their efficiency over their first three breeding seasons. Two groups of ewe lambs were bred at seven months of age at an average pre-breeding live weight of either 47.9 ± 0.36 kg (heavy; n = 135) or 44.9 ± 0.49 kg (control; n = 135). Ewe live weight, number of lambs born and weaned, and lamb live weight were recorded until 39 months of age, and efficiency was calculated for each ewe. Although the number and lamb weaning weight did not differ between treatments over three years, when data were pooled, heavier ewe lambs at breeding weaned a greater number of lambs over the three-year period. The total lamb weaning weight over the three-year period increased by 2% for each additional kilogram at ewe lamb breeding. Breeding heavier ewe lambs had no effect on efficiency. These results suggest that although breeding heavier ewe lambs had a positive effect on lamb production over the three-year period, it had no effect on efficiency. Before final recommendations can be made, lifetime performance and longevity to five years of age of heavier ewe lambs at breeding are required.