SELECTION FOR PREDICTED CARCASS LEAN CONTENT IN SCOTTISH BLACKFACE SHEEP

Scottish Blackface sheep have been selected for either increased or decreased predicted carcass lean content at 20 weeks of age, using an index combining ultrasonic backfat depth and body weight. The index was designed to alter carcass lean content without changing body weight. After 4 years there have been large responses in the index and fat depth, the proportional difference between the divergent lines in fat depth is 0.28, but body weight and ultrasonic muscle depth have not changed between the lines. The realized heritability for the index is 0.45. Heritabilities for the index, ultrasonic fat depth, body weight and ultrasonic muscle depth, calculated using multivariate restricted maximum likelihood, are 0.47 (s.e. = 0.14), 0.39 (s.e. 0.13), 0.23 (s.e. 0.12) and 0.36 (s.e. 0.14), respectively. The selected lines will be used to investigate relationships between carcass lean content, viability and maternal performance under the harsh environmental conditions encountered in the Scottish hill environment.