Developmental growth and body weight loss of cattle. III. Dissected components of the commercially dressed carcass, following anatomical boundaries

Abstract

This paper describes part of an investigation of the effects of developmental growth and body weight loss on the carcass composition of Angus steers. A method of anatomical dissection was used on one half (the right side) of each carcass to find the weights of each carcass component. The results are compared with those obtained from a method of dissecting butcher's joints used on the other (left) half of each carcass. Two groups of steers were used in this experiment: group A, which grew continuously, and group B, which grew like group A and were then subjected to a period of weight loss before slaughter. Corresponding animals in both groups were killed at the same body weights. Statistical analysis was by analyses of covariance of weights of components converted to logarithms. As carcass weight increased, the proportions of muscle, bone, and fascia and tendons decreased, while the proportions of the fat components increased. This result was similar to that obtained. previously by joint dissection, but the changes differed in degree. Distribution of muscle and bone changed significantly as the total weights of these components increased. Distribution of the other components was known only in so far as they came from either the hindquarter or the forequarter; no changes were found in their distribution as their total weights increased. Comparison of group A and group B animals at the same carcass weight showed that body weight loss led to a significant increase in the proportion of bone in the carcass but only a slight decrease in the proportion of muscle. Body weight loss had a differential effect on the proportion of kidney and channel fat in the carcass, the result depending on the weight at which animals were killed. The weight of subcutaneous and intermuscular fat in the group B carcasses did not vary significantly from that of group A carcasses of the same weight. These results were similar to those found by joint dissection but there were differences in magnitude. In particular, the differences in muscle weight between group A and group B carcasses was more pronounced in the joint dissection, where it was statistically significant. Also bone weight from the joint dissection was affected differentially by the weight loss treatment at the different killing weights; however, there was no evidence of a differential effect on bone weight in the anatomical dissection. These differences were ascribed to more accurate separation of tissues in the joint dissection. Distributions of muscle, bone, and fascia and tendon were affected by loss of body weight. Unlike joint dissection, anatomical dissection did not show significant effects on the distribution of subcutaneous fat and intermuscular fat due to the weight loss treatment; these differences between results are ascribed to differences between the units used for assessing these distributions.