Diverse lamb genotypes-1. Yield of saleable cuts and meat in the carcass and the prediction of yield.

Carcass measurements and composition data were obtained for 591 lambs representing two sexes (307 cryptorchid males, 284 ewes). The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams, crossed with Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (T × ELM, PD × BLM, T × M, PD × M, BL × M, M × M). m × M carcasses were significantly (p < 0.05) leaner than all other genotypes as measured by GR at a common weight, except for ewe carcasses where they were not significantly leaner than T × M carcasses. There was no difference in GR between Texel and Poll Dorset sired carcasses. The BL × M and PD × BLM carcasses were the fattest at the 5th rib. M × M lambs produced the lightest carcasses in each sex. Genotype differences were found for conformation using the EUROP scoring system. M×M lambs had a greater proportion (p < 0.001) of poorer scores particularly compared to PD × BLM and T × BLM carcasses. Analysis of Texel and Poll Dorset sired carcasses showed that the Texel cross had a better conformation than Poll Dorset cross amongst both sexes. BLM dams produced carcasses with a superior conformation compared to Merino dams (p < 0.001) in both sexes. BL × M carcasses had a significantly (p < 0.05) smaller M. longissimus thoracis et lumborum area (LL area) than other genotypes, except for M × M ewe carcasses. Texel sired ewe carcasses had a larger LL area (p < 0.05) than those sired by Poll Dorsets, but there was no significant difference for the heavier cryptorchid carcasses. Saleable meat yield for the BL × M carcasses of both sexes was significantly less (p < 0.001) than all other genotypes. M × M carcasses of both sexes produced similar amounts of saleable product to second cross carcasses with the T × M carcasses being superior, resulting in a significant sire breed effect. Texel sired carcasses produced more product than Poll Dorset carcasses. Year had a significant (p < 0.05) effect on all carcass measures and saleable meat yield. Genotype had a significant (p < 0.05) effect on the proportion of each cut except for the neck from cryptorchids and neck fillet from ewes. Texel sired genotypes had significantly (p < 0.05) heavier weights for the hindleg and forequarter cuts than those sired by Poll Dorsets. For the BL × M and m × M genotypes, some of the hindleg cuts, such as the topside and silverside weighed less than other genotypes. The boneless loins from the Poll Dorset genotypes were the heaviest, resulting in a significant (p < 0.05) sire breed effect, with all other genotypes being similar. Models were developed to estimate the yield of cuts and saleable meat using hot carcass weight, GR and other variables. The amount of variation in yield explained by hot carcass weight and GR ranged from r(2) = 0.06 to 0.23. Inclusion of LL area increased the r(2) values up to 0.39. Inclusion of both genotype and year significantly (p < 0.05) improved the prediction of yield, with year contributing the most. The addition of sex had no effect on the prediction of yield.