Consumer preferences for lean healthy meat have driven genetic selection for leanness in the terminal sire and dual purpose sheep industries over the last 20 years. The Invermay Coopworth lean and fat selection lines were established in 1980 to study the effects of selection for live weight adjusted leanness on carcass traits, and the correlated responses in other traits. This paper reports the findings of two year’s data on lamb survival and performance in the lean and fat selection lines. Records were collected from 817 lambs comprising 325, 337 and 155 from the fat, lean, and a random-bred control line, respectively. Neo-natal mortality was not significantly different between the three lines, with approximately 93% of lambs born surviving until tagging. Lamb survival from tagging until weaning differed significantly between the selection lines (P<0.05), with fat line animals having 10.9% better lamb survival than lean line animals (95.5 verses 84.6%), after adjusting for differences in year, birth weight, birth rank, skin thickness, wool length, age of dam, mothering ability and ewe udder volume. Fat line lambs were 0.9 ± 0.1kg (mean ± SEM) lighter than lean line animals, with control line animals intermediate. Udder volume (as measured by water displacement) did not differ between the three lines. Mothering ability (as measured by distance from ewe to the new born lamb during handling in the field) did not differ significantly between the lean and fat lines. Fat line lambs had thicker skins than lean line lambs at the same birth weight (P<0.01), but had no difference in wool length. The differences in lamb mortality between the lean and fat lines cannot be fully explained by differences in birth weight, indicating some physiological difference between the lines affecting survival.
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 61-64, 2000
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