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 ...

In this paper, the first of a series of three in which fat deposition is examined in 42 castrate male Hereford and Friesian cattle, details are given on the experimental material and procedures used in all papers. Whole body composition (anatomical and chemical) and the partitioning of fat within the body are also reported in this paper.Four, two and 15 animals were slaughtered at 6,13 and 20 months of age, respectively, after ad libitum feeding of a complete pelleted diet.TheFriesians were heavier than the Herefords, having 10%, 20% and 14% heavier empty bodies at 6, 13 and 20 months, respectively.At the same age, the Friesians had a greater percentage of empty-body weight as carcass muscle, carcass bone, total body water and total body ash than the Herefords but a lower percentage as dissectible fat and total body lipid. An analysis of linear body measurements showed no difference between breeds in the stage of development of external body dimensions at 20 months of age, and it was concluded that at the same age and stage of development of live weight or size, the Friesians were leaner than the Herefords.Relative growth coefficients of the fat depots showed late developmental growth in some intra-abdominal depots (omental and perirenal-retroperitoneal) but not in another (mesenteric). Relative growth coefficients of the omental, mesenterie and intermuscular depots were different between breeds. The Herefords deposited more dissectible fat subcutaneously than the Friesians whereas the Friesians deposited more in the intraabdominal depots. A multivariate index of fat partitioning, which was not influenced by age or stage of development of the fat depots, was not significantly correlated with fatness, suggesting no direct link between the pattern of fat partitioning and body-fat content.Breed differences in the distribution of fat within the subcutaneous and intermuscular depots were minor compared with the large difference in the partitioning of fat between depots. It was thus concluded that the factors controlling fat partitioning do not influence the distribution of fat within depots.

The insulin secretory response to tolbutamide was examined in cattle to determine: whether this agent is insulinogenic in this species, what effect age has on insulin secreting ability, and whether the insulin response is related to body fatness. Intravenous injection of sodium tolbutamide (27 mg kg-0.75) caused a three-to sevenfold rise in plasma insulin concentration, but the response was delayed and protracted in comparison with that seen in non-ruminants. The insulin response was higher at 20 than at 12 months of age. The insulin response was not related to the proportion of dissectible fat in the empty body, and it was lower in Hereford than Friesian steers despite the Herefords being slightly fatter. It was concluded that tolbutamide is insulinogenic in cattle and its effectiveness increases with age. Unlike the non-ruminant, there is no association between fatness and insulin response to tolbutamide in cattle compared at the same age.

The size and number of recognizable fat cells (diameters greater than 5 pen) were examined at several sites in 42 Hereford and Friesian steers. Four, two and 15 animals from each breed were slaughtered at 6, 13 and 20 months of age, respectively, after ad libitum feeding.For the 15 animals of each breed slaughtered at 20 months, biopsy samples of adipose tissue were removed at 10, 13 and 17 months from the 12th rib, midloin, rump and perirenal sites. Samples from these sites and from the brisket (subcutaneous), prescapular (intermuscular) and omental sites were also removed from the carcasses of slaughtered animals. Fat cell diameter (microscopic technique) and dry matter (from which lipid content was predicted) were measured on all samples. Measurement of fat depth (ultrasound) and surface area at the subcutaneous sites allowed changes in relative number of cells to be estimated during growth.From biopsied samples it was apparent that the perirenal depot grew almost exclusively through cell enlargement in both breeds. In contrast, the subcutaneous depot grew principally through cell enlargement to about 13 months of age and thereafter through both increase in number of cells and cell enlargement. The trigger for this increase in number of cells was possibly a critical average cell size, although this clearly did not operate in perirenal fat.Slaughter samples showed that cellularity changes with growth were similar in the perirenal and omental depots (intra-abdominal) whereas changes in the prescapular (intermuscular) site tended to parallel those in the subcutaneous depot.In relation to fat-free body weight (and therefore taking body size into account) both breeds had similar numbers of intra-abdominal and prescapular fat cells, but the Herefords had approximately double the number of subcutaneous fat cells compared with the Friesians. INTRODUCTIONRESULTS

AbastractMeasurements of live weight and of ultrasonic (Scanogram) fat depth and m. longissimus cross-sectional area at the 12th/13th rib were taken at 4— to 6-week intervals from 10 to 35 months of age (23 occasions) on 15 Hereford males (bulls), 15 castrate males (steers) and 15 females (heifers) managed under grazing conditions.Mean rates of live-weight change throughout the measurement period (0·51, 0·47 and 0·39 kg/day for bulls, steers and heifers, respectively) were significantly different. When compared at the same ages, fat depth was similar in the steers and heifers, beginning at about 3 mm and increasing to 11 mm. Fat depth changed little in the bulls, beginning at 1·7 mm and increasing to 3 mm. At the same age, bulls had larger m. longissimus cross-sectional areas than steers and steers had larger muscle cross-sectional areas than heifers.Absolute variation within sex groups increased throughout the experiment in live weight and fat depth, but not in m. longissimus crosssectional area. Simple correlation coefficients, pooled within sex groups, of relationships between the same measurements at various measuring occasions, indicated that measurements of fat depth and of muscle cross-sectional area at 10 to 12 months of age are poor indicators of these measurements at periods of 6 months or more later in life.When compared at the same live weights, heifers had the greatest and bulls had the smallest fat depth and, within animals, fat depth was closely related to live weight. At any live weight, m. longissimus cross-sectional area was less in heifers than in steers and bulls, which were not significantly different from each other in this trait. Equations relating fat depth and muscle area to live weight are presented and, under the conditions of this study, indicate that there is no basis for adjustment of fat depth for live weight in bulls subjected to contemporaneous selection.