Abstract

Five Poll Dorset breeders have co-operated since 1982 in a progeny-testing programme to improve lean meat production in their respective flocks. Ram lambs were selected from each flock on their BV's for weaning weight (in 4 of the 5 flocks) and were then assessed for fatness (visually and tactually initially, and finally by ultrasonic probe), structural soundness, and muscling. The ram lambs selected for the progeny test were mated at random to Coopworth mixed-aged ewes on a commercial prime lamb property. The progeny were identified to sire and dam and their birthrank indicated by ear-tag. Only progeny born during a 6- to 7-day period were identified in this way. At slaughter in November, information on export grade, carcass weight, and GR measurement was obtained. Heritabilities of carcass weight (CWT) and GR measurement adjusted for carcass weight (AGR) were respectively 0.20 and 0.29 and the genetic correlation between them was -0.09 (based on 29 sires and 490 progeny). To rank the sires, data were analysed on 3 criteria: AGR: carcass lean index (CLI); and a selection index (SI) which included estimates of the relative economic values of carcass weight and GR measurement. Use of CLI was expected to produce the greatest gain in CWT, but least reduction in GR while AGR gave the largest reduction in GR but little gain in CWT. Use of SI would result in intermediate gains in both traits and would achieve the highest increase in financial return carcass.

GC, Waghorn

Proceedings of the New Zealand Society of Animal Production, Volume 46, , 31-36, 1986