Abstract:
ESTIMATION OF CARCASE COMPOSITION OF BEEF BULLS L. G. WILLIAMS*, R. M. BUTTERFIELD and E. BELINDA DETTMANN* Summary A study was made of carcase composition in 47 Angus bulls within one herd two years. The half carcases of five bulls were dissected to check the validity of using prediction formulae previously devised for use on steer carcases. It was shown that the formulae were satisfactory for predicting the muscle:bone ratio in these bulls. The regression of muscle:bone ratio on carcase weight was 0.0055 k 0.0017 kg. The mean muscle: bone ratio adjusted to a carcase weight of 213 kg was 3.99 * 0.20. There was little variation in muscle:bone ratio among individuals and the differences between sire progeny groups were not significant. However, the number of progeny within each group was small and a wider sampling is required to establish the extent of the within breed variation in muscle: bone ratio. I. INTRODUCTION Within the cattle industry, the apparent difference in the relative size of muscles has long been of particular interest to breeders. However, the studies of muscle-weight distribution by Dumont, Le Guelte and Amoux ( 196 1) and Butterfield ( 1965a) indicated that there is little important difference in the relative size of muscles despite a wide range of different shapes in cattle. The major interest in muscle development is now in the total amount of muscle in the carcase which is conveniently expressed as muscle:bone ratio. Breed differences in muscle: bone ratio have been cited by Hankins, Knapp and Phillips ( 1943)) Carroll, Clegg and Kroger (1964), Anon (1966) and by Berg and Butterfield (1966). However, information is needed on the within-breed variation in this ratio. A programme has been commenced to build up phenotypic and genetic parameters of muscle:bone ratio to assess whether this character can be improved by selection. This paper presents preliminary information on the phenotypic parameters of muscle: bone ratio. This ratio was based on muscle and bone weights estimated from formulae developed by Butterfield (1965b). As these formulae were derived from steer carcases, their applicability to bull carcases was examined. II. MATERIALS AND METHODS Forty-seven Angus bulls, raised under uniform conditions at Trangie Agricultural Research Station, NSW, were used in this study. In 1966, there were 32 bulls, the progeny of nine sires, and in 1967 there were 15 bulls, the progeny of six sires. Three sires from outside studs were represented by progeny in both years. *N.S.W. Department of Agriculture, Sydney. TDepartment of Veterinary Anatomy, University of Sydney. 318 The bulls were reared on their dams at pasture to an average age of 180 days and then individually fed a standard concentrate ration & libitum for a further -180 days. They were slaughtered at an average age of approximately 420 days (range 356-461) on June 28, 1966 and July 4, 1967. Carcase weight of each animal was measured 30 h after slaughter. Carcases were quartered between the eleventh and twelfth ribs and fat thickness was measured over the longissimus dorsi muscle at points 6 and 12 cm from the mid-line. One shin from each of the 47 carcases was dissected into muscle and bone. Five half carcases from one sire group were totally dissected as described by Butterfield (19614). The shins and the five sides were carried by refrigerated transport from Sydney to jBrisbane. Calculations and analyses An estimate of the weight of fat, muscle and bone in the half carcase from each bull was made using formulae 2a, 3a and 5a in Table IX of Butterfield ( 1965b). These formulae were based on carcase weight, fat thickness and weight of the shin bone (radius and ulna) and associated muscle. The connective tissue weight and dissection loss were each estimated as 2% of half carcase weight. These values were added to the estimated weight of fat, muscle and bone to give the estimated total weight of the half carcase. To determine whether differences in muscle:bone ratio existed between sire progeny groups, the estimated muscle:bone ratios, adjusted for carcase weight as . covarrate, was analysed for variation between years, between sire groups within years, and within sire groups. The regression coefficient of muscle:bone ratio on carcase weight, after the effects of years and sire groups were removed, was calculated, and was used in adjusting muscle:bone ratio for each progeny group to a common carcase weight. III. RESULTS Table 1 shows the weights of various carcase components and the muscle: bone ratio of the five totally dissected half carcases, together with the differences between these actual figures and those estimated from Butterfield's formulae. The estimates for muscle were extremely accurate while bone was slightly overestimated. The overestimate of bone resulted in an underestimate of muscie:bone ratio. None of these differences was significant. The regression coefficient of muscle:bone ratio on carcase weight after the effects of sire groups and years were removed was 0.0055 -+ 0.0017 per kg (P<O.O5). Table 2 shows the mean figures for each sire progeny group for carcase weight, unadjusted muscle:bone ratio and adjusted muscle:bone ratio for both years. These are listed in descending order of adjusted muscle:bone ratio. There were no significant differences between years or between sires within years, for any of these characters, and the coefficients of variation were 9.5, 5.6 and 4.9% respectively. IV. DISCUSSION In general, the formulae provided satisfactory estimates of the carcase components in the five carcases dissected. However fat weight was consistently under319 TABLE 1 Weights of various carcase components and the ratio of muscle to bone weights of five half carcases, together with the difference between these weights and those estimated using Butterfield's (1965b) formulae estimated. This may be partly due to fat thickness measurement in the present study having been taken at the 1 l/ 12 rib site instead of at the lO/ 11 rib site used in Butterfield's formulae. In this connection Hedrick et aZ (1965) showed that fat thickness decreased from the eleventh to thirteenth vertebrae. Also, during dissection the impression was gained that the distribution of fat on * these bull carcases was different to steer carcases, in that a smaller proportion of the total subcutaneous fat lay on the dorsum of the carcase where the fat measurement was taken. Both the site of measurement and the possible difference of fat distribution probably contributed to the underestimate of fat. 320 TABLE 2 Mean carcase weights and mean muscle:bone ratios of bulls within sire progeny groups and years Carcase weight was significantly underestimated. This is partly explained by the underestimate in fat. Also the dissection loss, which from previous experience had been estimated at 2%, was higher in the present instance, probably due to transport of the carcases. The differences between estimated and actual half carcase weights for the five carcases dissected were very similar to those from the other 42 carcases. The differences were -5.2 1 + 1 .23 kg for the five carcases totally dissected, -5.22 & 2.15 kg for the remaining 27 carcases in 1966, and 4.94 t- 2.72 kg for the 15 carcases in 1967. Therefore estimates of carcase components derived from the formulae probably apply equally well to all 47 carcases. The difference between the estimated and actual muscle:bone ratio (3.4% of mean) is slightly less than the standard error involved in comparing sire progeny groups (4.9% of mean) and both these errors are small. Therefore, using these formulae we have estimated muscle:bone ratio with sufficient accuracy to enable useful comparisons to be made of sire groups. 321 The data presented here are limited, but it seems likely that there are only small differences between the muscle:bone ratios in the herd studied. This is in agreement with the findings of Vial (1966) who showed that muscle:bone ratio within breeds and crosses was relatively constant, indicating that there may not be sufficient variation within breeds to allow scope for selection. However, a much wider sample of many breeds is necessary before this generalisation should be accepted. The appearance of double-muscling in many breeds (Mason 1963)) with its much higher muscle:bone ratio (Neuvy, Vissac and Roustan 1962; Butterfield 1966)) indicates that the samples of breeds in which muscle:bone ratio has so far been studied may not adequately represent those breeds. V. ACKNOWLEDGMENTS Thanks are due to Mr. W. L. Mason for assistance in collection of records on the bulls and to Messrs. E. R. Johnson and D. A. Baker of the University of Queensland for assistance in dissection. The study was financed in part by the Australian Meat Research Committee. VI. REFERENCES (1966). Report of Major Beef Research Project. The Royal Smithfield Club, London. Underhill (Plymouth) Ltd. 53 pp. B ERG, R. T., and B UTTERFIELD , R. M. ( 1966). Anim. Prod. 8: 1. B UTTERFIELD , R. M. ( 1964). In 'Carcase composition and appraisal of meat animals.' (Ed. D. E. Tribe.) Tech. Conf. Melbourne. (C.S.I.R.O.: Melbourne.) B UTTERFIELD , R. M. ( 1965a). Proc. N.Z. Soc. Anim. Prod. 25: 152. 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