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An investigation was conducted on beef carcasses, aimed at identifying the growth patterns of wholesale cuts and their tissues in steer during fattening phase. This study involved 69 grass-fed steers with a liveweight range of 300 to 600 kg. They had entered, or were progressing along, their fat deposition phase. An allometric model (Huxley, 1932) was used to study the growth patterns of carcass tissues within wholesale cuts. In general, The growths of muscle and fat within wholesale cuts followed similar patterns. Some differences in growth patterns between muscle and fat were identified on the dorsal region. The growth impetus for fat moved from the thoracic backwards to the lumbar region which was the reverse of the growth impetus for muscle. Differential growth patterns occurred between intermuscular (IM) fat and subcutaneous (SC) fat. With IM fat, its growth movement was similar to that of total fat where there was a concentration of growth in the lumbar area and thin flank as side weight increased. With SC fat, there were growth movements from the ventral region to the dorsal region of the carcass. Bone growth within wholesale cuts showed a less clear pattern.

The accuracy of a single fat thickness measurement at each of five carcass sites and at the 10th and 12th ribs in estimating side fat weight and side fat percentage was determined in 36 steer carcasses. Three sites were associated with the fat layers of the split brisket, one was located at the caudodorsal angle of M. biceps femoris and one was situated 3 .O cm lateral to the highest point of the sacral crest. All three brisket sites were poor predictors of side fat weight and side fat percentage. The other four sites were of approximately equal accuracy in predicting side fat percentage, with residual standard deviations of: M. biceps femoris, 2.81 %; sacral crest, 3.07%; 10th rib, 3.12%; and 12th rib, 2.81 %. Side fat weight was predicted less accurately by M. biceps femoris (5.42 kg) than by sacral crest (4.50 kg), 10th rib (4.98 kg) or 12th rib (4.94 kg). Chilled side weight was a valuable addition in multiple regression analyses, significantly improving the residual standard deviations of all four sites, especially M, biceps femoris, in predicting side fat weight (M. biceps femoris, 1.56 kg; sacral crest, 3.54 kg; 10th rib, 3.31 kg; 12th rib, 2.84 kg). Only in the case of M. biceps femoris did the addition of chilled side weight improve the accuracy of prediction of side fat percentage (residual standard devation = 1.75 %). The reliability of the seven sites in accurately measuring fat thickness was determined in 3215 dressed carcasses in six abattoirs. Sacral crest was clearly the most useful site. In addition to being an accurate predictor of carcass fat, it could be measured accurately in 98.3 % of carcasses (or 94.3 % of sides), compared with 10th rib (83.9 % and 71.6% respectively) and 12th rib (82.9% and 68.5 % respectively). If the measurement of fat thickness at the 12th rib is used in the Australian Beef Carcase Classification Scheme, up to 21 % of carcasses (or up to 44% of sides) in some abattoirs will require alternative procedures to describe their fat status. Sacral crest fat thickness accurately estimated side fat weight and side fat percentage, and it provided reliable measurement in all but 1.7 % of carcasses; it is conveniently located if an alternative site to the 12th rib is required.

Ninety-five steers were used to develop a method of estimating the weights or percentages of the four carcass tissues—muscle, bone, fat and connective tissue—while the carcasses were still on the slaughter floor. From an investigation of a number of non-carcass parts it was found that three measurements could be used to estimate all four carcass components. The measurements were (a) short-cut tongue weight; (b) foreshanks weight; (c) hot side weight. Simple and multiple regression equations were developed to estimate the weights of muscle, bone and connective tissue in the chilled side, and the accuracy of the estimates was compared with that of recorded prediction methods. The most useful equations employed short-cut tongue weight and hot side weight to estimate total side muscle weight, and foreshanks weight to estimate both total side bone weight and total side connective tissue weight. Fat weight was estimated from hot side weight and the estimates of the weights of the other three carcass components. This technique was more accurate than the Australian Beef Carcase Appraisal System and Butterfield's equation, both of which use fat thickness measurement at the 10th rib. When fat thickness measurement was included in regression equations, the estimates of muscle weight and fat weight were slightly improved. Advantages of using the 'non-carcass parts' technique are as follows. All four major carcass components are predicted; the carcass components can be recorded as absolute weights or percentages of chilled side weight; chilled side components are predicted whilst the hot side is still on the slaughter floor; no commercial loss occurs in carcass, offals or by-products; all measurements used in prediction are weights; and fat thickness measurements may be included in the prediction. The additional information enables producers to make a more critical assessment of the nutritive performance and genetic progress of their herds.