Use of cold carcass weight and fat depth measurements to predict carcass composition of Rasa Aragonesa lambs

Abstract

A total of 22 measurements of fat depth, taken along the 13th rib, 5–6th lumbar vertebra, 3–4th sacrum vertebra, and the 2nd, 2–3rd, 3rd, 3–4th, 4th, 4–5th sternebra of the breast bone, were taken on intact carcasses with a sharpened steel rule, and related to the carcass composition of 18 Rasa Aragonesa lambs. The objective was to study the accuracy of these different measurements for predicting carcass composition and possible value, in the process of carcass grading or classification of ‘Ternasco’ Aragón lambs. Cold carcass weight (CCW) accounted for 74% and 40% of the total variation of muscle weight and total carcass fat weight, respectively. The addition of 4 cm fat depth over the 13th rib from the left side accounted for a further 13% of muscle weight, and the addition of 4 cm fat depth over the 5–6th lumbar vertebra from the right side accounted for a further 29% of the variation of total carcass fat weight. Regarding different fat depots, CCW accounted for 49% and 31% of the total variation of the intermuscular fat and kidney and pelvic fat, respectively. However, CCW alone only accounted for 21% (NS) of the total variation of subcutaneous fat weight, but the addition of 4 cm fat depth over the 13th rib from the right side or the addition of 4 cm fat depth over the 5–6th lumbar vertebra from the right side accounted for a further 47% of the subcutaneous fat variation. A comparison of the residual standard deviations (RSD) of the two measurements indicated that the fat depth over the 5–6th lumbar vertebra was more accurate for predicting subcutaneous fat. The highest precision, after CCW, for predicting intermuscular fat, was fat depth over the 13th rib from the left side, which accounted for a further 18% of total variation of this fat depot. Prediction of carcass composition was improved by the addition of fat depth measurements, assisting in the commercial classification of ‘Ternasco’ Aragón lambs.