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A study was made of the effect on body composition of growing Angus steers from 300 to 440 kg at three different rates. The rates were: High (H) 0-8 kg/day, Low (L) 0-4 kg/day and High-Maintenance (HM) 0-8 kg/day followed by a period during which body weight was maintained constant.The animals were individually penned and the different growth rates were achieved by controlling intakes of a pelleted feed. Two animals (part of H treatment) were killed at 300 kg and the remaining 27 animals (nine in each treatment), were killed at common body weights of 330, 363, 400 and 440 kg.Analyses of covariance were used to compare linear regression equations representing results from each treatment. In order to do this, the logarithmic transformation of the allometric equation, y = ax?, was used. As a proportion of empty body weight (EBW), hot carcass weight (HCW) was greater in both the HM and L groups than in the H group, indicating a greater offal component of EBW in the H animals. The loss in weight of the dressed carcass during storage at 2 °C for 24 h was similar in all three groups and was 0-98% of HCW. The proportions of HCW in the fore-and hind-quarters were similar in each group.At the same dissected side weight (DSW), the weight of bone was significantly greater in both the HM and L groups than in the H group indicating that bone development was related to both age and carcass weight. There were no significant differences between the groups in the proportions of either muscle or total fat. However, the proportion of kidney and channel fat in the H group was greater than in the HM and L groups and the proportion of subcutaneous fat was also greater in the H than in the L group. The amount of connective tissue in the three groups followed, in general, group differences in bone. Analyses of the dissected components of the separate fore-and hind-quarters showed that the difference between the H and L groups in the proportion of subcutaneous fat in the DSW was due to a relatively greater development of this fat in the fore-quarter of the H animals.No differences were found between treatments in the proportion of 'expensive muscles' relative to total side muscle (TSM). However, there were treatment effects on the proportions of TSM formed by certain groups of muscles; two examples are: the proportion of group 4 muscles (abdominal muscles) was higher and the proportion of group 6 muscles (distal muscles of the fore-leg) was lower in the H than in the L treatments. Bone weight distribution was similar in all treatments.There were differences between the H and HM groups in the relative growth ratios for all fat tissues (subcutaneous, intermuscular and kidney and channel fat) compared with total side fat. However, in the H and L groups, the relative growth ratios for corresponding fat categories were similar. The weight of kidney and channel fat in the left side of the carcass was significantly greater than in the right side of the carcass in all treatments.• Present address:

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.

This paper describes the effect of three different growth rates on some offal components of Angus cattle. The growth rates were: high (H, 0-8 kg/day), low (L, 0-4 kg/ day) and high-maintenance (HM, 0-8 kg/day followed by a period during which body weight was held constant).Equations are presented which enable the weights of the offal components to be calculated within the body weight range 300-440 kg.For most tissues, weights in the H group were greater than in the L and HM groups and included: liver, rumen-reticulum, small intestine and the total alimentary tract. Weight of fat trimmed from the rumen-reticulum, omasum, large intestine and total alimentary tract was also greater in the H than in the L and HM groups. The reverse situation held for head, feet and tail and the spleen.

Fourteen Friesian and 13 Angus steers, grown at pasture, were selected so that their carcass weights fell evenly throughout the range 200-300 kg. The right half of each carcass was dissected into muscle, fat, bone and fascia and tendon, and the left half boned-out and fat trimmed into retail cuts. A step-wise multiple regression procedure, including a pseudovariable for breeds, was used to compare compositional components on a common weight basis.Angus, at the lower end of the live-weight range, had heavier empty bodies than Friesians; at the heavier end of the live-weight range, this was reversed. This relationship between live weight and empty body weight was due to variation between breeds in the weight of contents in the fore stomachs but not the intestines.When compared at either the same live weight or the same empty body weight, Angus had more hot carcass than the Friesians (8-0 and 8-4 kg, respectively). There was no difference between breeds in loss of carcass weight in the 24 h post-slaughter.There was no breed difference in weight of blood, head, kidney and channel fat, kidneys, liver, diaphragm, heart, lungs, tail or fore-stomachs, when compared at the same offal weight. The feet and intestines were, respectively, 0-55 and 2-43 kg heavier for Friesians than for Angus at the same offal weight, but the pizzle was 0-11 kg lighter. Hide weight was greater in the Angus at all offal weights, with the difference between breeds being 0-016% of (offal weight) 2 .There was no difference between breeds in the weight of muscle or the weight of fascia and tendon when compared at the same dissected side weight; however, the Angus had 4-8 kg more fat and 3-0 kg less bone than the Friesians at the same dissected side weight.When compared at the same muscle weight the Friesians had 1-04 kg more proximal hind-limb muscles, 0-30 kg more proximal fore limb muscles, but 0-74 kg less abdominal muscles than the Angus. At all dissected muscle weights the Angus had a greater weight of muscles of the neck and thorax, and this difference increased with increasing weight of dissected muscle. The Friesians also had 1-52% more of their muscle as 'expensive muscle'. There were no breed differences in the distribution of any other muscle groups.There was no breed difference in the distribution of dissected fat between subcutaneous and intermuscular depots when these were the only fat depots considered. However, when kidney and channel fat was included in the total dissectable fat of the carcass, Friesians had 22-4 % more kidney and channel fat, the same weight of intermuscular fat and less subcutaneous fat than the Angus at the same total dissected fat weight.Friesians tended to have more of their bone weight in their legs (humerus, femur, tibiar-tarsus, radius-ulnar-carpus) and Angus more in their thoracic region (thoracic vertebra© and ribs, scapular and sternum-costal cartilages).At the same retail side weights there was no difference between breeds in the weight of fat-trimmed, boned-out, retail cuts; however, the Friesians had ...