Recent trends in carcase evaluation.

Abstract

RECENT TRENDS IN CARCASE EVALUATION (Invited Paper) G. C. EVERITT* The current change of emphasis from purely subjective commercial grading of meat carcases to more objective systems of appraisal is discussed. Modern methods of meat processing and marketing, together with rejection of animal shape as a factor of great productive importance, are considered dominating features of this change. The yield of boneless, fat-trimmed meat is rapidly becoming the criterion of commercial merit. Adoption of this criterion at carcase shows, in place of score cards based on linear measurements and visual appraisals, is urged. A need for standardisation of procedures is recognised. Universal acceptance of either a fat-free or 'fat-corrected' carcase is advocated in research work, with greater attention being paid to fundamental aspects of growth and the design of experiments. I. INTRODUCTION Meat is the end point of an intensely complex industry. It is also the commencement of another industry, equally intricate, involving processing, handling, storing, transporting and marketing the final product (Cockrill 1963). Lawrie (1962) emphasises the paradox that our direct enjoyment of the commodity lasts for only a few minutes although it may have taken years to produce. Unlike milk which is consumed in the natural state and which is a welldefined easily homogenised product, meat is distressingly heterogeneous in composition (Dumont 1965; Pomeroy 1965a) and in other 'quality' attributes. The evaluation of these organoleptic qualities of meat, which are affected by regional, national, and even local culinary habits, frequently defies biological interpretation (Doty 1960). These factors of meat quality have been reviewed recently (Renou 1962; Scheper 1962; Dumont and Renou 1965). This present contribution attempts to place in perspective the importance of cwcase evaluation to the producer, the processor and the consumer. It deals, in particular, with commercial carcase grades; their use and the reasons for change; and how these changes, in turn, relate to standards set in research investigations. II. CARCASE EVALUATION AND THE CONSUMER Recognition of differences in meat cuts and fatness extends back in antiquity-the loin, for example, being prized by heirarchical members of the Courtbut the real emphasis on improvement is a comparatively recent development. The quest for improvement is encouraged by the demand for meat which is influenced in large part by the accumulation of wealth. In the United States of America (U.S.A.), for example, beef imports largely from Australia and New *Ruakura Agricultural Research Centre, Private Bag, Hamilton, New Zealand. 268 Zealand (N.Z.) have increased by 100% in the last decade, accounting for about 10% of domestic consumption in 1964 (C.E.C. 1965). This dynamic demand for beef reflects a growing population and affluence that has increased consumption from 50-90 lb/head/year in 15 years. Selectivity of the consumer increases, however, as the demand and price rises and today there is a general appreciation of the close interrelations between efficiency of animal production on the one hand, and processing, marketing and consumption on the other. Rapid expansion of world transport and trade, coupled with demands for animal protein, has substantially increased the movement of meat and meat products at all levels of trade organisation. This trend will undoubtedly continue and the resulting diversity of consumer demand supports Friedlander' (1964) view that, 'The first important factor (in meat producs tion and research) is the necessity of breaking down the barriers previousl y existing between primary production, processing and marketing so that one can have a direct line of communication. . . . ' Study of isolated components of this integrated system is probably one further reason for our lack of progress for, 'Accuracy of appraisal decreases at each processing point along the chain from dinner plate to the live animal ' (Butler 1960). The spasmodic progress in meat production efficiency during the two centuries since Robert Bakewell (1725-1795) is also due to a lack of rational objectives, especially at the consumer level (Pomeroy 1965b). Dumont ( 1961) and Donald (1963) emphasise the difficult task facing the meat production geneticist. Numerous complex characteristics must be considered to cater for immediate needs. The technical and economic definition of the chosen characters poses serious problems. A forecast of the requirements 20-30 years hence must be made; and the great diversity of production methods and different environments should also be included in the appraisal. III. COMMERCIAL CARCASE EVALUATION Wardrop (1964) defines grading as, ' . . . a process which attempts to divide a heterogeneous group of material into sub-groups, within each of which the material has similar characteristics.' A recent report on meat grading in New Zealand comments, 'Efficient grading results in the producer being rewarded for the production of the grade of meat in greatest demand at particular times and in particular markets, and allows of the product being bought on its grade mark without inspection ' (M.E.G.I.C. 1965). Many of the basic principles of beef grading (Kiehl and 1960) are equally applicable to the grading of sheep and pig tion or shape, 'finish' or fatness, and 'quality' are three mining grade in all species. Each of these visually appraised close scrutiny. (a) Visual Appraisal Rhodes 1960; Pierce carcases. Conformamajor factors deterfactors is now under When reviewing carcase appraisal and meat grading, Hammond (1963) approved of subjectively applied grades although he recognised that, 'In all systems of grading, the details require to be aimed at a special market . . . and need to be revised from time to time to meet changes in public demand.' Australia 269 and New Zealand both export meat to many countries (Aust. Meat Bd. 1965; N.Z. Meat Prod. Bd. 1965). As each importing country has specific demands, graders are faced with a host of diverse requirements. Dumont (1965) notes that 'nationalism' is one of the limiting factors to advancement of knowledge in meat production and grading, for it leads to partial solutions which are not translatable to other countries. Bray (1963) suggests that although visual grade is one of the simplest and perhaps most used research tools, it is one of the most meaningless. Grading authorities in the U.S.A. (Fed. Reg. 1965) state that, 'The inability under the present Federal (visual) beef grade system to more precisely identify the yield of meat has forced many retailers to develop individual purchase specifications. Since each specification is slightly different the full force of competition cannot be directed against the total beef supply.' Visual appraisal of quality characters in pig carcases (Harrington 1958; Harrington and Pomeroy 1961; Gatherum, Harrington and Pomeroy 1958, 1961; Pomeroy 19658) although receiving some support (Bostock 1964) is rejected by others (Downey 1961; Fagan 1965). Buck (1963), for example, states, 'Visual scores . . . made on the shoulder, ham and streak and on the carcase conformation, bear no relationship to the proportionate weights or to the leanness of the respective parts of the carcase. They reflect only the requirements of the trade which are based on shape and are not substantiated by dissection.' Tayler and Rudman (1963) reached a similar conclusion for beef carcase grading in the United Kingdom (U.K.) where, according to Vial and Kelly ( 1963), there is a tendency to give a premium to fatter carcases which are associated with reduced lean portions and heavier bone. The last authors conclude, 'There is little sense in a grading system which penalises the farmer producing lean carcases, and at the same time forces butchers to charge higher prices than are necessary to allow for trimming of superfluous fat.' More recently, in the U.K., results on some 5,000 graded beef carcases have been examined (Anon. 1965); the weights of wholesale joints and the actual prices realised were related and it was found that, ' . . . the current grading system did not reflect the relative value and profitability to the producer or wholesaler.' This statement tallies with the fact that one wholesale organisation in the U.S.A. opposed the introduction of new grade standards on the basis that the high yielding, high quality beef carcases they were buying would cost them 5 U.S. dollars more if they were identified and sold on the basis of their value (Fed. Reg. 1965). Edwards (1965), reviewing dairy beef production, states, 'Grading standards of the past have become outmoded and where they remain in spite of change of taste they are increasingly ignored and by-passed by meat buyers.' The reasons are clear. In the U.S.A., beef carcases of the same weight and visual quality grade showed differences of up to 179% in yields of trimmed, boneless retail cuts, with a correspondingly -wide difference in value. Differences in the Choice grade, for example, of more than 15 U.S. dollars existed (Fed. Reg. 1965). Pierce (1960) quotes examples of differences in value between individual beef carcases of over 10 U.S. dollars per 100 lb carcase weight or over 601 U.S. dollars per carcase. In N.Z., Barton (1965a) has found variation of comparable magnitude in Aber270 deen Angus steers of the same age and carcase grade with price differences amounting to nearly 25 N.Z. shillings per 100 lb carcase weight. Lamb carcase visual grading is likewise inefficient (Barton 1965a; Timon 1965), although the process has received less attention and criticism than beef. This may be partly because the magnitude of any financial discrepancy will be so much less for an individual lamb than beef carcase; and partly because lamb is most commonly retailed bone-in. The variation within visual grades of lambs may, in fact, be greater than for beef, for the grader has a far greater number of carcases to appraise within a given time. Seebeck (1965) concluded that there was a definite bias in the grading of Australian lambs within sex, breed of sire and age at slaughter discriminating against lighter leaner lambs. Other Australian (Robinson, Binet and Doig 1965) and N.Z. (Kirton 1964a; Ann. Rep. 19641965) work with sheep supports this contention. Timon (1965) comments, 'Usefulness of subjective grading (of lamb carcases) is questioned as all of the carcase scores were biased towards, and almost completely determined by, level of fatness in the carcase.' Breeders of pedigree stock still valiantly defend the value of shape in their animals (Jones 1964), but there is a mass of scientific evidence refuting conformation as a factor of productive importance. The distribution of muscular tissue is very similar in animals of widely different conformation (Butterfield 1964). Shape appears closely related to the amount and distribution of fatt y tissue in beef cattle (reviewed Everitt 1964; Riggs 1963; Butterfield 1965a; Dumont, Guelte and Arnoux 1961; Guelte, Dumont and Arnoux 1964), sheep (Boccard et ctl. 1961; Timon 1965) and pigs (reviewed Harrington 1958). Kirton (1964a), at Ruakura, paired 28 lamb carcases on the basis of conformation and carcase weight. Each pair contained one carcase of 'very poor' and one carcase of 'very good' conformation. He found that, ' . . . these figures do not support the commonly held belief that carcases of better conformation contain more muscular tissue. In fact the results suggest that the carcases classified as having good conformation contained more fat.' In view of this wealth of evidence, it is surprising to find recently a report (Arbuckle and Alexander 1965) advocating a points system for judging live cattle at Australian shows. The authors state, 'Since judging is usually done largely on the basis of trade suitability, (shows) serve as a means of telling the producer what type of carcase is currently required by meat processors.' Butler (1960), in contrast, believes, 'Fat slaughter cattle that look very similar alive are likely to show marked variation in carcase muscling. This is of major concern to the beef industry.' Judging meat animals on their ultimate yield of edible meat (Everitt 1961; Barton 1965~) would appear a more progressive procedure. Work with the pig carcase is not at variance with this general theme (Carroll 1964). Fredeen, Bowman and Stothart (1955) concluded, ' . . . relationships obtained in this study strongly suggest that the tapered ham is leaner, a more desirable type, and that the present ideal of a plump ham, well-filled in the upper portion, actually favours the fatter ham.' This latter suggestion is surely of substantial importance to the Australian and N.Z. lamb industries. The shape of the hind leg constitutes one of the principal criteria for subjective carcase evaluation; 271 it is believed that, at the same carcase weight, short legs have a more developed musculature than long legs. Scientific evidence now refutes this view (Boccard et al. 1961; Kirton 1964a). It is interesting to note, too, that the shape of the hind limb and, in consequence, that of the carcase, the two being closely linked, has no influence on the principal organoleptic characteristics (Boccard and Radomska 1963). The question can therefore be raised, 'Is the plump hind leg so avidl y sought by the N.Z. producer of cross bred lambs more, or less, acceptable today than the tapered leg seen to advantage in the Merino-type lambs of Australia?' The answer may lie in the method of presentation to the consumer. Where the commodity is marketed bone-in, a shapely leg is of some interest, as those who have experienced carving joints will know. But, on a boneless fat-trimmed basis, interest in shape rapidly fades. Here it must be recognised that there is a growing trade in boneless lamb cuts (N.Z. Meat Prod. Bd. 1965) resembling the early stages in development of marketing boneless fat-trimmed beef (Ever& 1961). It is noteworthy that about 90% of Australian mutton exports inI 1962-63 were in boneless form (McKay 1964), while Colebrook (1965) predicts a great increase in the consumption of manufacturing meats in the U.K., resembling the trend in the U.S.A. Grade standards, then, have not developed in response to expressed consumer interests but have been largely supported by meat producers and processors. Producers expected to benefit by using grades to tap a larger share of the consumer budget. It has rarely been questioned whether the grading standards taken from wholesale market practices have provided guides for maximising either efficiency of production or consumer expenditure and satisfaction. In the post-war struggle for markets between meat production areas, and between animal species, basic principles of the grading procedures have been challenged. Large scale studies have been undertaken. An illustration is the development (Ramsey, Cole and Hobbs 1962) of Yield Grading now operating for beef in the U.S.A. (Fed. Reg. 1965), with variants of the scheme under active consideration in the U.K. (H.M.S.O. 1964) and N.Z. (M.E.G.I.C. 1965). This attempt at uniformity of grading standards, with the virtual exclusion of visual appraisals, and the general recognition of a basic code of requirements will do much to foster international trade and render its expansion. Application of economic incentives for producers would hasten the process of acceptance. As the recent report on grading in N.Z. (M.E.G.I.C. 1965) states, 'Emphasis on cutability as the main criterion in beef grading should secure the most rapid improvement in the quality of beef. It will bring home to farmers and drafters the need to avoid excessive finish thus eliminating costly trimming and therefore producing cattle most likely to show a greater return.' It is, however, difficult to reconcile this tacit acceptance of yield grading in beef with continued support for visual grading of lamb (M.E.G.I.C. 1965). (b ) Objective Appraisal Assessment of the yield of boneless, fat-trimmed cuts in beef-or 'cutability' - i s estimated in the U.S.A. by consideration of four characteristics: (i) amount of external subcutaneous fat; (ii) amount of kidney, pelvic and heart fat; (iii) area of the longissimus dorsi muscle cross-section; and (iv) carcase weight. 272 The cutability group, or yield grade, of carcases, quarters or cuts is determined from appropriate regression equations (Fed. Reg. 1965). Butterfield (196%) has developed and used (Clark et crl. 1964) regression equations for estimating carcase composition based on carcase weight, fat thickness over the Longissimus d~rsi muscle and the weight of the dissected radius/ ulna bone and associated muscles. Callow (1962) also found that foreshin dissection allowed estimation of carcase composition. Subcutaneous fat measurements were associated with two to three times as much variation in retail yield as were measurements of the longissimus dorsi muscle cross-section in the recent study of Hedrick et 02. (1965). The combination of yield grading with classification by specifications (Charles 1964; Charles, Butterfield and Francis 1965) has much to commend it. A system of classifying and marketing beef by specification of sex, age, weight and approximate carcase composition, .as indicated by fat cover, is proposed. As Charles (1964) comments, ' . . . this system would encourage the production of better quality beef no matter what the definition of quality in a particular trade. Demand for certain specifications must eventually result in higher prices being paid for the most suitable meat for current markets.' Application of specification buying to lamb warrants attention. IV. CARCASE EVALUATION IN RESEARCH The objectives of many meat production investigations are similar to those of commercial grading; namely, the identification of animals producing edible meat most efficiently. Many of the principles underlying current revision of grading schemes originate from research programmes as, for example, in yield grading of beef. Confusion, however, has resulted from not knowing precisely what is required and this has, in turn, affected considerations of productive efficiency. The objectives of carcase evaluation in research are defined by Pomero y (1965a) as the measurement of the amount and distribution of various tissues (bone, muscle and fat) in the carcase. Dumont (1961) emphasises that optimum meat production in a technical sense is an inadequate definition and an economic component is also needed. He proposed the following parameter: Q (C-R) T where, Q C1 R= TC suggesting However, . . . (1) weight of carcase in kg sale price of carcase in kg cost price of carcase in kg time (years) taken for production it was sufficiently schematic for interpreting meat production efficiency. as Dumont points out, the expression suffers from parochialism. This scheme of appraisal can moreover be criticised on the grounds that carcase weight is of variable composition. Such a formula breaks down if a large proportion of the carcase is the most expensive product but of least demand273 fat. Berg and Butterfield (1965) propose that the percentage of fat in the carcase could be used as an index of marketing acceptability; this is an indirect measure of the proportion of muscular tissue in the carcase. A second parameter, again forwarded by Dumont (1961), is thus superior: Weight of Muscle Given Age . . . (2) and this can be reasonably extended to include the food intake required for production: Weight of Muscle per unit of food intake . . . (3) Given Age for 1 kg of muscle requires 1000 kcal compared with 8600 kcal for the production of 1 kg of fat (Witt 1961) with no evidence of genetic differences in the productive requirement (Nehring, Schiemann and Hoff man 196 1). Model (3) satisfies two objectives. It approaches the requirement for lean meat; and it clarifies the objectives of experimental work. The last objective is important for the carcase weight as a sole parameter of performance can be 1963). expressed consumer nutritional and genetic use of live weight or misleading (Luitingh One disadvantage of using rate of live-weight gain is that it makes no distinction between gain associated with skeletal growth and gain associated with muscular development (Gibson and Watson 1963). Another more serious disadvantage is variable fatness. Hargrove (1963) compared the performance of Brahman, Shorthorn and their first crosses adjusting the carcases to a fat-constant basis of 1297 kcal/lb using the method of Meyer (1960). A striking change in ranking order of the breeds was recorded depending upon the inclusion or exclusion of fat in the comparison. Hargrove comments, 'The point is that animals must be produced with the genetic potential of storing the proper amount of fat or economy of production will be lowered.' Martin and Torreele (1965) found that the variation within breeds of dual-purpose cattle was greater than between breeds in most of the carcase characters studied. At a given weight or age, animals of larger mature size will gain more rapidly on less feed than animals of smaller mature size, and, further, carcases of the larger animals will contain a higher proportion of bone and muscle and a lower Froportion of fat (Kidwell and McCormick 1956; Mason 1963, 1962, 1964; Langlet 1965). These facts underlie the current marked interest in such breeds as the Friesian and Charolais for beef production. Recent investigations reveal that breeders of British-type breeds of cattle have succeeded in developing animals that will store a large amount of fat at a young age. Bond et ul. (1965), for ` example, compared several breeds and crosses under different planes of nutrition and reached the startling conclusion that, 'The Angus was the most efficient breed in fat production'; a conclusion supported by the studies of Witt (1965). There is little reason to suppose that breeders of British-type meat-producing sheep have performed differently. 274 Cole et ul. (1964) examined the effect of type and breed of British, Zebu and dairy cattle on beef production and concluded, 'These results depict the role that fat plays in depressing % separable muscle, separable bone and protein and the yield of major untrimmed wholesale joints among breeds', a conclusion in line with other studies (reviewed Everitt 1964; Holme 1963; Guelte, Dumont and Arnoux 1964; Hedrick et al. 1965). Current research in the U.K. on the use of Charolais sires on dairy cows suggests that, ' . . . the apparently much greater efficiency of food conversion of the Charolais crosses from British breeds can be largely though not entirely explained by the difference in the degree of finish of the c;-asses compared (Boyd, D. A.; personal communication). Luitingh (1963) and Luza? (1964) agree that the whole problem of efficiency of growth and fattenin2 is complicated by lack of knowledge of the nature, and therefore the energy value, cf the gains during specific periods. A solution to this problem must be found before any absolute energetic efficiency values can be calculated. The solution will need to be sought in techniques of assessing body and carcase composition of animals, with special reference to the proportion of fat. It is not intended to deal here with the battery of techniques now in use; these have been reviewed elsewhere (Bray 1963; Hedrick et al. 1963; Morris and Moir 1964; Panaretto 1964; Kirton 1964b; Timon and Bichard 1965; Joblin 1965). The search for correlations will continue. Greater attention does need to be given to fundamental aspects of growth and development, especially where these can be integrated with practical aspects of carcase evaluation. The studies undertaken by Pomeroy (1965a) and others (Butterfield 1965a; Butterfield and Berg 1965b) are good examples in this connexion. The recent challenge of traditional concepts of growth (Elsley, McDonald and Fowler 1964; Tulloh 1964a), with revived interest in allometric principles (Boccard, Dumont and Lefebvre 1962; Tulloh 1964&b; Butterfield and Berg 1965a,b; Everitt and Jury 1965), provides a sound basis for a renewed approach. The current belief that excess nutrients at any stage of growth are converted into fat (reviewed Lucas 1964) and that rapid rates of gain in the early stages of fattening may be detrimental to carcase quality. (Boccard and Duplan 1961; Henrickson, Pope and Hendrickson 1965; Duckworth 1965; Fowler 1965) illustrates the need for further nutritional studies involving carcase evaluation. Investigations of 'abnormal ' conditions may indicate profitable methods of improvement in normal meat-producing animals. Muscular hypertrophy (reviewed Lauvergne, Vissac and Perramon (1963), or hyperplasia, as suggested recently (Butterfield 1965c), is a good example. Basic features of this condition are a high proportion of tender muscle; a large muscle:bone ratio, with a low proportion of fat- all highly desirable features. The condition shows variable expressivity but it is interesting that it is most clearly recognised in those breeds of cattle at present in great demand for beef production (e.g., Charolais, Limousin). Can the anatomical and physiological components of this condition be recognised in other species and breeds of meat-producing animals and, if so, what is the extent of their heritability? The design of experiments involving a measure of carcase composition and eval uation also needs reviewing. Several of the classical meat-production experi275 Fig. 1. -Relative growth of chemical components in lamb carcases. (From Everitt and Jury 1965; reproduced by kind permission of the Editor of the Journal of Agricultural Science.) $8 = Entire male. 8 = Castrated male. QQ = Entire female. Q = Spayed female. ments have recently been criticised on grounds of design and analysis (Buck, Harrington and Johnson 1962; Elsley, McDonald and Fowler 1964; Tulloh 1964.a). An experiment examining the effects of sex and gonadectomy on the growth and development of lambs (Everitt and Jury 1965) was of comparative slaughter design with sequential sacrifice of small numbers of individuals in 276 Fat-Free Carcase Weight (kg) Fig. 2.-Relative growth of chemical components in fat-free lamb carcases. $8 = Entire male. 8 = Castrated male. QQ = Entire female. Q = Spayed female. (From Everitt and Jury 1965: reproduced by kind permission of the Edltor of the Journal of Agricultural Science.) 277 place of the slaughter of a large number at one time or weight. Figure 1 shows that this design yielded useful information on carcase compositional changes, while Figure 2 indicates the small variation in chemical composition of the lamb carcases on a fat-free basis. Moreover, such a design permits evaluation of the time taken to achieve a specified level of carcase fatness. Pomeroy (1965a) proposes such a sequential slaughter pattern so that by statistical methods animal performance may be compared at a constant level of carcase fatness. Since the level of fatness affects considerations of feed conversion efficiency (Meyer 1960; Witt 1961, 1965), carcase composition and conformation (Tayler and Rudman 1963; Tayler 1964; Everitt 1964) and meat quality (Renou 1962), it is vital that this should be standardised in any given experiment. The difficulties of interpreting trials terminated on either weight constant, time constant or equal 'finish' bases have been discussed by Pomeroy (196%) and Dinkel et al. (1965). The last workers also deprecate the use of ratios and percentages involving weight as a denominator-a conclusion in line with Tulloh's (1964cr,b) proposals. Use of a 'fat-corrected' carcase where weight gains are adjusted (by covariance analysis) to equal energy content (reviewed Meyer 1960) appears desirable. Lofgreen (1965) finds this a superior procedure to using weight gain, or weight gain in association with dressing-out percentage and grade. The ultimate objective should be to base all comparisons on either a fatcorrected or a fat-free carcase basis. Either procedure approaches the requirements of model (3) proposed earlier. V. CONCLUSIONS The fact that shape is quite largely determined by the amount and distribution of fat, leading to the rejection of conformation as a factor of great productive importance by scientists, if not pedigree breeders, represents a notable recent trend in carcase evaluation. Fat is in least demand by consumers; it affects the yield and distribution of lean meat; and at the same time it is energetically most expensive to produce. There seems little point, therefore, in the continuation of traditional breeding policies. Rapid growth rate, coupled with high feed conversion efficiency, leading to maximum muscle production represent parameters of greatest importance. Meat animals need to be appraised on their yield of muscular tissue, or at least edible meat, and the use of score cards based on linear measurements and visual appraisals seems unprofitable. Standardisation of procedures is urgently needed in commercial and research spheres of evaluation. Greater attention needs to be paid to the composition of weight change. Acceptance of a fat-corrected or fat-free carcase would lead to considerable progress. Techniques for evaluation of body and carcase composition continue to warrant the substantial support l of research authorities. As Mason (1964) aptly comments, 'There are no short cuts to the desired end. . . . ' 278 IV. DISCUSSION Variation in the timing of birth in relation to the drying off of pastures and in the age at weaning, has been accompanied by differences in growth and wool production which have persisted for at least two to three years. Furthermore, the different early treatment appears to have resulted in differences in reproductive performance at two years of age. Differences in wool production and Iiveweight at the first post-weaning shearings were probably associated with differences in age between groups, but at later shearings, age differences were of minor importance. Although the number of ewes per group was small, differences in reproductive performance were likely to occur because of differences in liveweight at mating (Coop 1962). It is not possible to decide from these observations whether the differences in results were a consequence of the timing of birth in relation to seasonal nutritional stress or of differences in age at weaning, but it seems likely that the former factor was the more important. Certainly Watson and Elder ( 1960) did not find that early` weaning of lambs pasture had any adverse effect on growth and Briggs ( 1964) showed that crossbred and fed a high protein diet grew as fast diet. 249 and McLaughlin (unpublished data) (at lo-12 weeks of age) on to mature relative to unweaned lambs. McInnes lambs weaned at seven weeks of age as unweaned lambs offered a similar B UTTERFIELD , R. M. , and B ER G, R. T. (19653 Relative growth pat terns of corn tnercially important muscle groupsl of cattle. R esearch in Veterinary Science (in press). CALLOW, C E. H. (1962). The relationship bet ween th e weight of a tissue in a single joint and the total weight of the tissue in a side of beef. Animal Production 4: 37. , M. A. ( 1964). Commercial cut-out and carcase composition of pigs killed at 200 lb. and 260 lb. live weight. Proceedings IOth European Conference on Meat Research, ARROLL Copenhagen. C.E.C. ( 1965). Meat-a review. Commonwealth Economic Committee, page 1. (London: H.M.S.O.). C HARLES , D. D. (1964). Classifying trade beef by specifications. Australian Veteri