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 we re sired by a selection of Texel (T), Poll Dorset (PD), Border Leicest er (BL) and Merino (M) rams, crossed with Border Leicester x Merino (B LM) and Merino (M) ewes giving 6 genotypes (Tx BLM, PD x BLM, T x M, P D x M, BL x M, M x M). M x M carcasses were significantly (p<0.05) lea ner than all other genotypes as measured by GR at a common weight, exc ept for ewe carcasses where they were not significantly leaner than T x M carcasses. There was no difference in GR between Texel and Poll Do rset sired carcasses. The BL x M and PD x BLM carcasses were the fatte st at the 5th rib. M x M lambs produced the lightest carcasses in each sex. Genotype differences were found for conformation using the EUROP scoring system. M x M lambs had a greater proportion (p<0.001) of poo rer scores particularly compared to PD x BLM and Tx BLM carcasses. Ana lysis of Texel and Poll Dorset sired carcasses showed that the Texel c ross had a better conformation than Poll Dorset cross amongst both sex es. BLM dams produced carcasses with a superior conformation compared to Merino dams (p < 0.001) in both sexes. BL x M carcasses had a signi ficantly (p < 0.05) smaller M. longissimus thoracis et lumborum area ( LL area) than other genotypes, except for M x M ewe carcasses. Texel s ired 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 x M carcasses O f both sexes was significantly less (p < 0.001) than all other genotyp es. M x M carcasses of both sexes produced similar amounts of saleable product to second cross carcasses with the T x M carcasses being supe rior, resulting in a significant sire breed effect. Texel sired carcas ses produced more product than Poll Dorset carcasses. Year had a signi ficant (p < 0.005) effect on all carcass measures and saleable meat yi eld. Genotype had a significant (p <0.05) effect on the proportion of each cut except for the neck from cryptorchids and neck fillet from ew es. Texel sired genotypes had significantly ( p < 0.05) heavier weight s for the hindleg and forequarter cuts than those sired by Poll Dorset s. For the BL x M and M x M genotypes, some of the hindleg cuts, such as the topside and silverside weighed less than other genotypes. The b oneless loins from the Poll Dorset genotypes were the heaviest, result ing in a significant (p < 0.05) sire breed effect, with all other geno types being similar. Models were developed to estimate the yield of cu ts 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 significa ntly (p < 0.05) improved the prediction of yield, with year contributi ng the most. The addition of sex had no effect on the prediction of yi eld. (C) 1998 Elsevier Science Ltd. All rights reserved.