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The weights of eight muscles or muscle groups, excised from the left side of the carcasses of 43 mature Hereford cows, were used to derive an estimate of total carcass lean. The standard deviation for the individual muscles ranged from 0.41 to 1.64 lb. of lean as compared to 18.63 lb. for total carcass lean. Sixty-four to 92% of the variation in total separable carcass lean of mature cattle was associated with the weight of certain entire muscles. With slaughter weight held constant, the standard partial regression coefficients obtained between the weight of the total carcass lean and the weight of certain muscles or muscle groups were: Biceps femoris, 0.97; sirloin tip muscle group, 0.82; Longissimus dorsi, 0.79 and inside round group, 0.72. The regressions of total carcass lean on the weight of the Biceps jemoris, Longissimus dorsiand the major muscles in the sirloin tip or inside round were 12.36, 10.24, 16.27 and 14.31 lb. of lean, respectively. High interrelationships were found among the weights of all muscles studied. The results indicate the validity of using the weight of certain entire muscles to estimate the degree of muscling in a particular mature beef carcass.

Relationships among 12 production and carcass traits and regression equations to predict BSRM were computed from records on 231 calves sired by Hereford, Brahman, Santa Gertrudis, Charolais, Charbray and Brown Swiss bulls, and separately for 74 Hereford calves.All traits were positively correlated with carcass weight and BSRM. For all breeds combined, carcass weight held constant, partial correlation coefficients of l. dorsiarea, length of body, kidney fat, fat thickness and carcass grade with BSRM were 0.50, 0.35, −.58, −.54 and −.19, respectively.Carcass weight was the most accurate single predictor of BSRM (r=0.94), followed by length of body (R=0.88), final weight (R=0.85), length of leg (R=0.78), width of round (R=0.77) and l. dorsiarea (R=0.76). As much as 95% of the variation in weight of BSRM was accounted for when several of these traits were combined in the same model along with kidney fat or fat thickness at the 12th rib. Length of body, length of leg, width of round and carcass weight accounted for 92% of the variation in weight of BSRM. As much as 84% of the variation in weight of BSRM was accounted for by certain production traits.