Developmental growth and body weight loss of cattle. IV. Chemical components of the commercially dressed and jointed carcass

Abstract

This paper describes a study of chemical components of the carcasses from Angus steers. The left side of each carcass was jointed commercially and each joint was analysed for protein (N x 6.25), water, ash, and fat (ether extract). Two groups of steers were used, viz. 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 weight. Statistical analysis was by analyses of covariance of the weights of components converted to logarithms.

As carcass weight increased, the proportions in the carcass of protein, water, and ash decreased while the proportion of chemical fat increased. When carcass composition was calculated on a fat-free basis, there were significant changes in the proportions of protein, water, and ash as the weight of the fat-free carcass increased during the age range of 12 to 24 months. These are contrary indications to the theory of chemical maturity put forward by Moulton (1923). As carcass weight increased, the weight of each chemical component increased but changes occurred in the distribution throughout the carcass of protein, ash, and chemical fat.

The effect of the weight loss treatment on the proportion of each chemical component was independent of carcass weight. When group A and group B animals were compared at the same carcass weight, weight loss led to a significant increase in the proportion of ash and a significant decrease in that of protein. The weight of ash in group B carcasses was estimated to be slightly less than that expected in these animals at their peak of body weight, i.e. before weight loss commenced. There were significant differences between groups A and B in the distribution of the chemical components (particularly protein and fat); these treatment differences in distribution indicate a limitation to the use of chemical analyses of a single joint for predicting whole carcass composition.

When relationships between chemical and dissected components were studied, each single chemical component was well related to its corresponding dissected component. For each dissected component except muscle, however, there were significant differences between groups A and B in the equation of best fit, either in slope or in the intercept (difference between adjusted means). Differences of this type limit the use of chemical analysis for estimating dissected components where differences between groups are being studied.