Effect of Feed Intake Level and Influence of Breed and Sex on the Relationships between the Physical Composition of the Bovine Carcass and Specific Gravity

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Abstract
Relationships between the physical composition of the carcass and specific gravity were established for two breeds of cattle fed ad libitum or 65 to 70% ad libitum. Holstein and Angus bulls, steers and heifers were slaughtered at body weights ranging from 120.7 to 706.7 kilograms. Specific gravity and physical composition of the right side of the carcass were determined. Level of feed intake did not influence relationships between physical composition and specific gravity, whereas sex (P<.01) and breed (P<.01) influenced the relationship between percentage muscle and specific gravity. The relationship between percentage fat and specific gravity was different (P<.01) for each sex. Although breed did not statistically alter the latter relationship, a higher degree of accuracy for predicting the percentage carcass fat was observed for Angus than for Holsteins. Breed also influenced (P<.01) the relationship between percentage bone plus tendon and specific gravity. The same relationships between physical composition and specific gravity were computed using animals containing a minimum of 12% separable carcass fat. The removal of lean carcasses resulted in an improvement in the accuracy of prediction of percentage fat. Chilled carcass weight combined with specific gravity as a second independent variable resulted in an improvement in the prediction of carcass composition, expecially in Holsteins. In bulls of both breeds, bone proportionality altered (P<.01) the relationship between the percentage fat and specific gravity. The relationships between the percentages muscle, fat and bone plus tendon in the carcass and specific gravity were linear. Carcass components expressed as percentages of the carcass side were not more highly correlated with the reciprocal or square of specific gravity than with specific gravity. Because of large standard errors of estimate, it is suggested that specific gravity should be used to predict the composition of groups of carcasses rather than that of individual carcasses.