LIVE ANIMAL ULTRASONIC MEASUREMENTS OF SUBCUTANEOUS FAT THICKNESS AS PREDICTORS OF BEEF CARCASS COMPOSITION

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Abstract
Data on the total dissectible muscle and fat tissue from primal cuts of the left hindquarters of 356 crossbred steers and heifers, and from the entire left side of 98 Shorthorn steer carcasses were used to evaluate the usefulness of subcutaneous fat depth measurements between the 11th and 12th ribs for predicting carcass composition. Analyses revealed that the use of multiple fat depth measurements from different sites on one or both sides conferred no advantage over the use of the best single measurement. The major sources of variation in total weight of muscle and fat tissue from the crossbreds were breeding group, sex and weight. The residual variances remaining after adjustment for these sources of variation were significantly reduced (P < 0.05) by inclusion of a single fat measurement with reductions of 12.5% (muscle) and 22.0% (fat) provided by the carcass fat measurement and 7.1% (muscle) and 13.1% (fat) for the Krautkramer measurement. For the Shorthorn steers, line and weight were the major sources of variation and larger reductions in the residual variances (16.3% for muscle and 24.6% for fat) were obtained by inclusion of carcass fat in the model. The ultrasonic fat measurements were less effective than carcass fat and the Scanogram gave larger reductions in residual variance than the Krautkramer (e.g., 8.1 vs. 3.9% for weight of muscle tissue). The results of this study suggest that live animal ultrasonic measurements of subcutaneous rib fat depth can be used to achieve modest improvement in predictors of beef carcass composition.