PREDICTING THE WEIGHT OF LEAN MEAT IN LAMB CARCASSES AND THE SUITABILITY OF THIS CHARACTERISTIC AS A BASIS FOR VALUING CARCASSES

The carcasses of 138 lambs were dissected into fat, muscle and bone as the basis for developing a model to estimate the weight of lean meat (muscle and intramuscular fat). The lambs represented two sexes (70 we thers, 68 ewes) and three sire genotypes (67 Poll Dorset, 39 Suffolk, 32 Wiltshire Horn) all from Border Leicester X Polwarth X Booroola typ e ewes. Hot carcass weight (HWT) was found to explain the majority of the variation in the weight of lean meat. When measures of subcutaneou s fat depth at different sites were used as predictors in addition to HWT, the accuracy with which lean meat yield could be estimated was fo und to increase by a small amount. There was, however, little differen ce in their individual value as predictors. The area of the M. longiss imus thoracis et lumborum at the twelfth-thirteenth rib was found to a ccount for the significant breed type difference between Poll Dorset a nd Suffolk sired lambs when included in a multiple regression with HWT and the GR measurement (tissue thickness at the twelfth rib 110 mm fr om the midline). The final model produced an R2 = 0.92 and an RSD = 0. 45 kg for the 106 lambs. Using the model for the 106 lambs, the estima ted (from the model) and actual values of lean meat for the Wiltshire Horn sired lambs were compared. The correlation coefficient between th e values was r = 0.97 and the RSD was 0-31 kg. This shows that for sec ond cross lambs as used in this study the fitted model exhibits a degr ee of general validity and stability. An overall model for the 138 lam bs produced an R2 = 0.92 an RSD 0.43 kg. The potential for pricing mea t on the basis of lean meat yield is discussed, with particular emphas is on the current developments in assessment of lamb carcasses in Aust ralia.