Use of sire referencing schemes to select for improved carcass composition in sheep

Objective genetic improvement in specialized meat breeds of sheep in Britain is based largely on the performance recording and genetic evaluation service provided by Signet and the Meat and Livestock Commission. This includes the use of ultrasonic scanning and a selection index to identify animals with high genetic merit for lean growth. More than 20 sire referencing schemes (SRS) have been established in Britain during the last 12 yr. About half of the performance- recorded flocks in Britain now belong to SRS. Sire referencing schemes create genetic links between flocks and years through the shared use of elite rams (reference sires), often via AI. Multitrait animal model BLUP is then used to provide across-flock genetic evaluations. These in turn allow increased selection intensities and increased response to selection. High responses to index selection for lean growth (about 1.75% per annum in the specialized meat breeds) and other measures of performance are being achieved