Lamb carcass characteristics. 2. Estimation of the percentage of saleable cuts for carcasses prepared as 'trim' and traditional cuts using carcass weight, fat depth, eye muscle area, sex, and conformation score

Abstract

Carcass data were obtained for 172 lambs (86 ewes, 86 cryptorchids) of hot carcass weight (HCW) 16.2-28.7 kg and fat depth at the GR site (12th rib) 5-21 mm. Of these, 85 carcasses (42 ewe, 43 cryptorchid) were prepared into the full range of boneless, heavily trimmed cuts ('trim' lamb) and the remaining 87 (44 ewe, 43 cryptorchid) into traditional, trimmed bone-in cuts. Two methods of determining M. longissimus thoracis et lumborum area (EMA) produced strongly correlated results (r = 0.94; P<0.001). Conformation score using the EUROP system (1 is best, 5 is worst) was negatively correlated (r = -0.31 to -0.53; P<0.05) with measures of EMA and HCW, which were positively correlated (r = 0.64-0.71; P<0.001). Leg length was positively correlated (r = 0.36-0.76; P<0.001) with measures of EMA and HCW. Models were developed to predict the percentage yield of saleable cuts for carcasses prepared into a range of trim and traditional cuts. These identified GR as the most significant variable, so models based on GR were developed for each yield type. HCW and EMA significantly (P<0.05) improved the accuracy of estimated yield in addition to GR. By contrast, when HCW and measurements of subcutaneous fat depth over the eye muscle (FDC) were combined, EMA was not significant (P>0.05). For estimation of the percentage yield of traditional cuts, conformation score as given by an assessor significantly (P<0.05) improved the accuracy of estimation when combined with HCW and FDC. This model indicates that as conformation score increases, yield increases. Overall in terms of predicting yield, conformation score was of little value when combined with currently used carcass measures. There was a significant (P<0.05) effect of sex on the prediction of yield for 2 combinations of trim cuts that included the eye of loin. Sex also influenced (P<0.05) the prediction of yield based on traditional cuts. Where sex was significant, ewe lamb carcasses had less saleable meat by <0.5-1.0%, depending on yield type. For 4 of the trim cuts (boneless loin, eye of loin, fillet, shoulder blade), EMA added significantly (P<0.05) to the estimation of the proportions of the cuts; at constant carcass weight and fatness as indicated by GR, increases in EMA are predicted to lead to an increase in the proportion of loin cuts and a decrease in shoulder blade. For carcasses prepared into traditional cuts, EMA added significantly (P<0.05) to the estimation of leg, midloin, forequarter, and shank cuts. In all cases the coefficient was positive, indicating that increases in EMA would lead, at constant carcass weight and fatness (GR), to an increase in the proportion of these cuts in the carcass. The amount of variation (R2) explained for the individual trim cuts ranged from 0.08 to 0.72 using models that included independent variables HCW, GR, and EMA, and which accounted for the effect of sex. For traditional cuts the values ranged from 0.28 to 0.79.