Prediction of the lean content of lamb carcasses of different breed types

Abstract

Carcass data for 424 castrated male lambs, comprising seven breed-type groups, were used toevaluate a series of linear measurements, subjective scores and the lean content of sample joints as predictors of percentage lean in carcass. The groups represented the main types of British lamb and mean carcass weights ranged from 12·8 kg (Welsh Mountain) to 20·8 kg (Lowland Longwool). Lambswere selected from commercial abattoirs to cover the ranges of fatness and conformation normally found in practice within each group. The pooled within-group S.D. for percentage lean was 3·70 and theoverall S.D. (ignoring groups) was 3·96.Predictors were compared in terms of precision and the stability of their prediction equations. Of the characteristics measured on the intact carcass, subjective scoring of external fatness gave the most precise prediction both within groups and overall (R.S.D._within = 2·82, B.S.D._overall = 3·17). Fat thickness over the eye muscle (0) was the best predictor among those taken on the quartered carcass (R.S.D._within = 2·76, R.S.D._overall =3·00). The most precise individual predictors were percentage lean in the best end neck and shoulder joints (R.S.D._within = 1·51 and 1·59 respectively). Among pairs of predictors not involving dissection, the combination of C and percentage kidney knob and channel fat in the side gave the most precise prediction (R.S.D._within = 2.51, R.S.D._overall = 2·68). The stability of the prediction equations between groups tended to increase with the precision of the predictors. Among the more precise predictors, the equation for percentage lean in the leg was a notable exception, being particularly variable from one group to another.