Estimations of Lamb Carcass Cutability within Narrow Ranges of Weight and Fat Thickness

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Abstract
CUTABILITY data from 577 lamb carcasses were subdivided into 13 groups based on ranges in carcass weight or into 14 groups based on ranges in subcutaneous fat thickness. Regression equations were computed to identify optimal subsets of three or four independent variables for predicting percent bone-in, closely trimmed primal cuts within each of the 27 strata of carcasses. Optimal subsets of carcass measurements predicted cutability with 3.9 to 16.2% and 1.5 to 7.8% greater accuracy than regression analyses using U.S.D.A. yield grade factors within specific fat thickness strata and specific weight strata, respectively. Correlation data revealed that among strata of carcasses based on narrow ranges in weight and even among carcasses which were similar in fat thickness, differences in fatness have the most profound influence on cutability. Among carcass weight strata, leg conformation score was a more reliable indication of muscling in lighter weight carcasses, while longissimus muscle area was a more important predictor of cutability among heavier carcasses. Increased fatness associated with heavier lamb carcasses undoubtedly affected leg conformation scores and compromised their reliability in relating the effect of differences in muscling on cutability. Optimal subsets of independent variables for predicting cutability within all of the fat thickness strata included both longissimus muscle area and total fat measure. Eleven of the 13 optimal subsets of independent variables for predicting cutability within carcass weight strata included longissimus muscle area and total fat measure per se while the other two subsets included these same two variables expressed as a function of carcass weight. The U.S.D.A. yield grade equation is sufficiently accurate for estimating cutability within narrow carcass weight ranges if the carcasses vary in fatness. However, among groups of carcasses varying little in subcutaneous fat thickness, factors other than those included in the U.S.D.A. yield grade equation (e.g. longissimus muscle area, carcass weight, kidney and pelvic fat weight) enhance the accuracy with which cutability can be estimated.

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