Estimation of the carcass composition of yearling bulls of "Asturiana de los Valles" breed from the dissection of a rib joint.

To evaluate different methods of estimating bovine carcass composition, seventy yearling bulls of the "Asturiana de los Valles" beef breed were slaughtered and their carcass composition estimated by a commercial dissection of the right half-carcass and by tissular dissection of the 6th and 10th rib of the left half-carcass. Correlation and regression analyses were used to identify the most accurate predictors of carcass composition. In simple regression, the percentage of lean in the 10th rib was the most accurate predictor (r=0.88; P<0.001) of the lean proportion in the carcass and the percentage of fat in the 6th rib was the best predictor (r=0.90; P<0.001) of the carcass fat content. The correlation coefficients for estimating the bone percentage in the carcass from the bone proportion in the ribs (6th and 10th) were low (r=0.63 and 0.51 respectively), although significant (P<0.001) and the coefficient improved when the proportion of lean in the ribs was used as predictor (r=0.78 and 0.70 for the 6th and the 10th rib respectively). In multiple regression, the addition of more regressors of the rib composition and carcass traits, such as carcass hot weight, the carcass fatness score and the weight of the kidney knob and channel fat, led to an improvement (P<0.05) in accuracy for some predictions. The results in general show that the accuracy of the predictions for the carcass composition obtained from dissection of both the 6th and 10th ribs was similar, although the dissection of the 10th rib tended to overestimate the proportion of fat in the carcass. Therefore, considering the carcass quartering method for the extraction of the ribs, it is proposed that dissection of the 6th rib is more appropriate than dissection of the 10th rib so as not to reduce the carcass value and obtain a good estimate of the carcass composition.