Expected selection responses in lamb carcass composition and weight

G.L. Bennett, J.N. Clarke

Ruakura Animal Research Station, Ministry of Agriculture and Fisheries, Hamilton

Proceedings of the New Zealand Society of Animal Production. 1984, 44: 243-248

Expected rates of genetic change in lamb growth and composition were calculated for 2 different selection goals; increase in lean growth rate (LRG) and decrease in weight-adjusted % fat (APF). Carcass fatness was measured in a number of ways on an animal's own or its relatives' performance. Under either selection goal, all selection programmes resulted in reduced % fat adjusted for age. All selection programmes for either selection goal improved lean weight but there was little improvement over selection for live weight alone. Alternatively, use of fat measurements did not decrease lean weight improvement and resulted in leaner carcasses. Changing carcasses from 13.5 kg and 25% fat to at least 15 kg and no more than 24% fat was most quickly achieved by selecting against APF.

Keywords: NZSAPAB; Sheep; carcass; genetic change; selection; fat; growth; ultrasound; specific gravity; clones

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