GENETIC-RELATIONSHIPS BETWEEN PREDICTED AND DISSECTED CARCASS COMPOSITION IN SCOTTISH BLACKFACE SHEEP

Carcass composition was measured on 133 Blackface ram lambs from a flock divergently selected for predicted carcass lean proportion. Prediction equations for different carcass components were developed using combinations of live weight and ultrasonic backfat and muscle depth. Both carcass lean and carcass fat proportion were best predicted using only live weight and fat depth, and a genetic transformation of the equation predicting carcass lean proportion was highly correlated (genetic correlation = 0.97) with the index on which the sheep were selected. Weights of carcass tissue were more accurately predicted than proportions. Lean weight was best predicted using live weight and mu scale depth, and the weights of different fat components were best estimated using live weight, muscle depth anf fat depth.

The equations predicting carcass lean proportion, carcass fat proportion, lean mass and fat mass had heritabilities of 0.29, 0.27 0.20 and 0.23, respectively. Heritabilities for carcass lean and carcass fat proportions, and the subcutaneous and intermuscular fat components were 0.43, 0.48, 0.24 and 0.49, respectively. Genetic correlations of the equation predicting carcass lean proportion with lean and fat proportions were 0.52 (s.e. 0.21) and -0.45 (s.e. 0.22), respectively. The same correlations for the equation predicting carcass fat proportion were -0.47 (s.e. 0.22) and 0.57 (s.e. 0.21). The equations predicting carcass lean and fat proportions were strongly correlated with subcutaneous fat proportion but weakly genetically correlated with intermuscular fat proportion.