Use of ultrasound in prediction of carcass characteristics in lambs

Abstract

Longissimus muscle area, maximum depth and maximum width and subcutaneous fat thickness were measured ultrasonically at the first lumbar vertebra on 1162 lambs. Lambs were rams, ewes and wethers, ranging in age from 3 to 15 mo, with liveweights ranging from 32.5 to 70.2 kg. Subjective conformation scores of the leg, loin and shoulder and body-wall thickness at the GR site (11 cm from the carcass midline between the 12th and 13th ribs) were measured on warm carcasses and were used to determine lean-meat yield. Saleable-meat yield and percentage of saleable-meat yield in each of the primal cuts were also determined by carcass dissection of 57 of the lambs. Stepwise regression equations predicting GR and lean-meat yield from ultrasound measurements, age, (age)2, liveweight and (liveweight)2 had an R2 of 0.49 and 0.47, respectively (P < 0.15). Stepwise regression predicting saleable-meat yield by carcass dissection from ultrasound measurements, age, (age)2, liveweight and (liveweight)2 had an R2 of 0.64, with subcutaneous fat as the only significant regressor (P < 0.001). Stepwise discriminant analysis used to predict leg, loin and shoulder conformation scores from ultrasound measures, liveweight, (liveweight)2, (age)2 and age had R2 values of 0.27, 0.18 and 0.24, respectively (P < 0.15). From these data, ultrasound measurements of subcutaneous fat and longissimus depth in combination with liveweight and age appear to be valuable predictors of saleable-meat yield as determined by carcass dissection, GR and lean-meat yield but appear to be less useful in prediction of subjective muscling scores, except in the case of small-frame lambs. Key words: Ultrasound, lamb, carcass, meat yield