Lamb survival traits in Coopworth sheep selected for high or low
backfat depth
N.B. Jopson, G.J. Greer, W.E. Bain, J.A. Findlay and J.C. McEwan
AgResearch, Invermay Agricultural Centre, Private Bag 50034,
Mosgiel, Dunedin
Proceedings of the New Zealand Society of Animal Production.
2000 60: 61-64
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.
Keywords: NZSAPAB;
Sheep; selection; leanness; survival
Last Updated 12-07-2000
