NEW Z E A L A N D LAMB A N D MUTTON RESEARCH

Transcription

1 159. NEW Z E A L A N D LAMB A N D MUTTON RESEARCH R. A. BARTON a n d A. H. KRTON* MASSEY AGRCULTURAL COLLEGE. MEW Z E A L A N D n this review, recent work only will be considered and most emphasis will be placed on the development of techniques and the assessment of their efficiency. The research work has been directed chiefly towards obtaining a clearer understanding of factors affecting the fatness of meat animals, and as sheep in our country are relatively cheap and often overfat, they have been used as the animal on which various procedures have been tried. t is also believed that much of the information obtained on the sheep will provide a valuable background to planning work on other species. t is becoming more evident that in many animal nutrition and meat production studies an accurate assessment of the body and/or carcass composition of the experimental animals is essential. Most of the procedures used in the past to obtain information on composition have suffered from the serious disadvantage of being costly in terms of manpower, time and materials. For example, the Cambridge school of workers in their use of the technique of complete dissection of the carcass have estimated (Palsson 1939) that it requires 72 to 84 man hours to separate the primary tissues of the whole sheep carcass. The physical separation used by American workers has likewise been considered expensive and time consuming. Similarly, chemical analysis of the whole body or carcass of meat animals has hitherto been regarded as a task beyondthe financial and labor resources of many laboratories. Determining the Chemical Composition of Carcasses The personnel of the meat laboratory of the Sheep Husbandry Department, bbssey Agricultural College, have been using a method for quickly and accurately determining the chemical composition of sheep carcasses and bodies (Barton and Kirton 1956; Kirton and Barton 1958a; Kirton, Ulyatt and Barton 1959; Kirton, Barton and Rae 1960). The methodinvolves a meat bandsaw to cut completely the frozen carcasees into slices each about 1/8 to 1/4 inch thick. The slices, while still frozen, are ground in a commercial grinder of 1 h.p. capacity with a cutting plate having 1.2 cm holes. The tkiceground material consisting of muscle, fat, and bone, is sampled for subsequent chemical analyses. For a determination of the composition of a side, six samples each of 50 g. of' ground material have been taken in the past and these are weighed into aluminum butter moisture cups. The samples a r e dried in an oven at 1O511O0C. for approximately 18 hours and then weighed to give water loss by difference. Following this weighing, liquid fat is poured off, petroleum ether i s added and the residue *. Present address: C/o Animal Husbandry Department, Michigan State University, East Lansing, Michigan..

2 160. crushed with a metal rod. After settling, the ether, containing the extra fat, is decanted off. T h i s process is repeated twice m r e and then the residue is returned to the oven to drive off the remainirq ether. The residue is then weighed to give the dried residue weight directly and the uncorrected fat weight by difference. To enable correction factors for total chemical fat and ash to be applied to th? previously crudely estimated constituents, subsamples of each residue are taken and usually bulked on a side basis. These subsamples are ground to a powder in a hammer mill. Two samples of the powdered material are dried at 105OC. and then Soxhlet extracted in petroleum ether for six hours. Further samples of the powdered material are placed in a muffle furnace to give ash contents. Fromthe fat and ash percentages in the crude residue, together with the weight of each residue, it is possible to calculate the weights of fat and ash in each crude residue. This fat correction figure is then added to the uncorrected fat weight to give the total weight of chemical fat in the original 50 g. samples. The weight of crude residue minus the fat correction weight and minus ash weight gives an.estimate of the weight of protein in the 50 g. sample. These procedures are also carried out for each joint. Usually all the dried residues of one classification of joint (such as loin) in a treatment group would be bulked and one fat correction and one ash determination are made for the group. t is of some pertinence to mention that there is a very high correlation between protein as determined by the previously mentioned method and protein as detemined by the Kjeldahl method (Ulyatt 1960). The correlation coefficient for 39 pairs of observations = The regression equation is: Y= X 0.07, SY.X method and X = = 0.14 lb protein, where Y = protein by Qeldahl protein (dried fatfree, ash free residue). Epficiency of Chemical Determination Recently a series of 20 lamb carcasses was used to asaess the efficiency of these procedures in determining the chemical composition of carcasses (Kirton, Barton and Rae 1960). L e f t and right sides were separately analysed as sides and as four parts, viz. leg, loin, 91011rib cut, and fore. t was found that the weights and the mean percentage composition of the two sides over the 20 carcasses were similar, Each of the four parts were also closely similar between sides except for the residue per cent. and protein per cent. of the loin in which the left side was significantly higher than the right side. n all the uncorrected chemical components a significant side X carcass interaction was found. An analysis of the sampling errors showed that the variance of a treatment mean was decreased only slightly by sampling both sides of the carcass instead of one. However, if the experimental requirement is for very precise determination of the composition of an individual carcass, then analysis of both sides would be necessary whenever it was desired to reduce

3 161 the standard error of a carcass mean below 0.54 for water per cent., 0.69 for fat per cent. (ur'corrected) and 0.42 for residue per cent. The variance due to differences between samples within a side was also shown to be satisfactorily small and therefore only a negligible improvement in precision would be obtained by increasing the number of samples per side. Thus two, instead of six, samples each of 50 g. of ground material would be suf'f'icient to adequately estimate the composition of the carcass under most experimental conditions. Relationships between Chemical and Dissectible Components of the Carcass A question often considered by various groups of workers is whether chemical procedures are preferable to dissection. t is well realized that dissection nto the three primary tissues of the carcass, viz. bone, muscle, and fat does give information of value to the animal husbandman and the butcher, but it may lack precision and also repeatability within and between laboratories. However, dissection may give informtion which cannot be obtained by chemical methods. Accordingly, work has been directed towards relating data obtained from dissecting one side of a mature ewe carcass with those obtained from chemical analyses on the other side of the same carcass. These relationships have been calculated for 39 carcasses (Ulyatt 1960) and the results are set out in Table 1. Table 1. RelationshiEbetwcen Chemical and Dissecsble Components of Mutton Carcasses (39 pairs of observations). Dependent Variate ndependent Variate (dissectible component) (chenical componen l r S Regression Equation y. X = 3*29X X = Fat w t (lb) Fat w t (lb) Y Muscle w t (lb) Protein w t (lb) Y Muscle wt (lb) Water w t (lb) Y Total Bone w t (lb) Ash w t (lb) Y = 1.04X 1.11X All the relationships except that between bone weight and ash weight are very high and therefore chemical determination of fat, protein, and water can replace dissection in order to obtain weights of fat and muscle in the carcass. t is clear, however, that a better prediction of bone weight is required than is possible from ash weight alone, The weight of the cleaned left metacarpal bone (cannon bone) can be used as an index of total bone in the carcass. The correlation between cannon bone weight and total bone in the carcass is and the regression equation is: Y = 0.15X X = , S = 0.44 lb., where Y.X cannon bone weight in g. Y total bone weight in lb. and

4 This relationship is a little better than bone weight and ash weight but still not satisfactory enough for accurate predictive purposes. t is suggested (Ulyatt 1960) that bone weizht and tendon plus "waste" weight be obtained as a residual after fatty tissue and muscle weights have been predicted from chemical fat and protein (or water) weights. ndices of Carcass Composition n many experiments it is not possible to determine the composition of the whole carcass because of the costs involved and also because of the number and size of animals used. These limitations have forced many workers to search for satisfactory indices of the composition of the whole carcass. Work in New Zealand has been active in this direction and the following indices have been examined. 1. Carcass weight n many meat production experiments, carcass weight is the sole objective criterion used to assess treatment effects. t occurred to the present authors that there may well be strong relationships between carcass weight and the components of the carcass. To this end data which had accumulated n the laboratory were analyaed to determine the relationships between the dissectible components of the carcass and its weight; similar relationships were determined f o r chemical components. 40 /. 0 a L a 30 C LA. d) c.p Y 0 w 2.ca 20 Y.t 0l O YO Carcass Weight b Fig. 1. Relationship between weight of carcass dissectible fat and carcass weight of ewe mutton (25 observations). 90

5 163. t w a s found (Barton and Kirton 1958b) t h a t there were highly significant correlations of the order of 0.9 bgtween dissectible f a t t y t i s sue and carcass weight (see Fig. 1) and between dissectible muscular t i s s u e and carcass weight f o r laub and ewe and wether mutton carcasses. The correlations of f a t t y t i s s u e o r chemical f a t with carcass weight a r e higher than t h e correlations of dissectible muscle, water o r protein with carcass weight. The standard errors of estimate of the regression equation range from 1.0 lb. t o 2.9 lb. and t h i s cannot be regarded as capable of giving highly accurate prediction. t should sfso be mentioned t h a t correlations between f a t, e i t h e r chemical o r dissectible, arid carcass weight have been calculated f o r c a t t l e, hogs and guineapigs (Barton and Kirton 1958b) and i n a l l cases t h e relationships a r e high. t would seem reasonable t o suggest however, t h a t other indices of carcass composition must give m r e accurate prediction than carcass weight if they are t o be of any r e a l use. 2. Samp l e j o i n t s The physical and/or chemical analyses of sample j o i n t s of carcasses are well established techniques f o r evaluating treatment e f f e c t s on the various components of the carcass. n sheep studies, the l e g and the l o i n singlycr i n combination have been most frequently examined and the dissectible components (fat, muscle, and bone) from these j o i n t s have been r e l a t e d t o the same components i n the whole carcass. The dissection data pertaining t o 50 ewe and wether mutton carcasses and 70 lamb carcasses f o r which weights of bone, muscle, and f a t on an anatomical j o i n t basis were available f o r the study of the accuracy of sample j o i n t o r j o i n t s as indices of t h e physical composition of the whole carcass. t was shown (Barton and Kirton 19582) t h a t t h e components o f the l e g o r t h e l o i n j o i n t s singly o r i n combination were very highly correlated w i t h the same components i n t h e whole carcass. The two j o i n t s i n combination gave b e t t e r predictions of the composition of the whole carcass than d i d either j o i n t considered separately. n t h z sheep, the l e g and t h e l o i n a r e both r e l a t i v e l y easy j o i n t s t o dissect and as they represent t h e highpriced p a r t s of the carcass t h e investigator studying them i s accordingly paying g r e a t attention t o an important region of t h e carcaes. Admittedly t h e destruction of t h i s region o f the carcass may represent a serious financial loss i n some experiments. t must be emphasized, however, t h a t i n s p i t e of the reported high degree of relationship between t h e various d i s s e c t i b l e components of any sample j o i n t and the same components i n the carcass, caution must be taken i n using such j o i n t s i n a l l experiments. For instance, Preston and Gee (1957) and Kirton and Barton (1958a) have shown t h a t i n sheep i m planted w i t h hexoestrol and thyroxine respectively there was a d i f f e r e n t i a l response evoked i n the l e g and i n t h e l o i n by hormone treatment. f e i t h e r j o i n t had been used individually as a sample of the whole, then a different picture would have been presented f o r the e f f e c t s of the

6 164 treatments on the main t i s s u e s of t h e whole carcass. t i s conceivable t h a t a chosen sample j o i n t m y not show a treatment e f f e c t whereas another sample j o i n t o r indeed the whole carcass may show very marked treatment effects. n another experfment involving 20 lamb carcasses, t h e use of s a p l e j o i n t s on a chemical r a t h e r than on a dissection basis was studied using the s l i c i n g and grinding technique and analysing samples of the ground meat including bone. Sanrples from the leg, t h e loin, t h e r i b cut and t h e reminder of the carcass were analysed f o r fat, protein, water, and ash. n t h i s case it was shown (Kirton and Barton 1960) that t h e l o i n and t h e r i b cut were the most suitable regions t o use as indices of the composit i o n of t h e whole carcass. t i s of i n t e r e s t t o record t h a t the slicing, grinding, scuppling and chemical work involved i n any of these four j o i n t s would not exceed one t o oneandahalf hours i n t o t a l. 3. spe c i f i c gravity The specific gravity of carcasses and of t h e i r j o i n t s has been considered by many workers as giving a useful indication of t o t a l f a t. Several experiments have provided opportunities f o r determining t h e specific g r a v i t i e s of both lamb and mature ewe carcasses and i n each experiment total f a t has been determined using the normal procedures of t h e laboratory involving s l i c i n g and grinding of t h e material. n most cases t h e correlations between specific gravity and t o t a l fat of the carcass have been high, that is, 0.8 o r b e t t e r Bee Fig. 2 (Barton and Kirton 1956; Kirton and Barton 1958b; Kirton and Barton 1960; Ulyatt 1960). The relationships between spscific gravity of t h e j o i n t s and t h e i r fat content, were, i n general, lower i n these studies than were t h e relationships f o r the whole carcass. There a r e limitations t o t h e r e l i a b i l i t y of specific gravity as an indicator of f a t content and these have been discussed by Kirton and Barton (1958b). These workers have shown that t h e method i s not suffici e n t l y accurete f o r individual carcass determinations p a r t i c u l a r l y a t the lower levels of fatness. The standard e r r o r s of estimate of fat were over 3 per cent., f o r water over 2.5 per cent. and f o r protein over 0.6 per cent. which a r e a l l disappointingly high f rom t h e standpoint of accurate prediction. 4. Leameter The efficiency of the l e a m e t e r instrument as devised by Purdue University workers, has been assessed using t h e sheep (Ulyatt 1960). Readings of f a t depth on the l i v e sheep using t h i s instrument when stat i s t i c a l l y analysed have demonstrated highly significant differences between sheep and significant differences between probe sites and nonsignificant differences between observers. When t h e mean of three leanmeter readings taken a t the shoulder, loin, and r q has been correlated with the depth of subcutaneous fat a t t h e t h r e e s i t e s on t h e dressed carcass it was found t h a t r : f o r 35 pairs of observations.!the mean of t h e three leanmeter readings has been correlated with weight of diss e c t i b l e f a t (r ), with weight of chemical fat i n the carcass (r = ), with d i s s e c t i b l e fat per cent. ( r = ), with chemical

7 165, a. 98 Fig O s. E. ru*y5$ YO Percent F a t Y Relationship between per cent. chemical fat i n ewe carcasses and carcass specific gravity (57 observations). f a t per cent. (r = ), with muscle weight (r ) and with muscle per cent. ( r ). Although a l l correlations are high the standard e r r o r s of estimate of t h e corresponding regression equations are large. Thus present r e s u l t s suggest t h a t the leanmeter w i l l give an indication of t h e f a t content of a group of sheep rather than an accurate estimate of t h e f a t content of an individual sheep. Outline of Some Recent Shheg_nvestigations A t the outset of t h i s paper it was stated t h a t much of the research effort has been directed towards obtaining a clearer understanding of f a c t o r s affecting the fatness of meat animals. The magnitude of the problem has been outlined by SmithPilling and Barton (1954); Barton (1957) and Barton and Kirton (1958a). Attempts have been made (Kirton and Earton 19582) t o reduce the l e v e l zf fatness of ewes before slaughter by implanting p e l l e t s of Lthyroxine and by imposing a low plane of n u t r i t i o n throughout a 28day period p r i o r t o slaughter. Neither treatment produced a significant reduction i n t h e fat content o f t h e carcass although l i v e weight losses of up t o 2 3 lb. over the period were achieved. Further investigations of the influence of l i v e weight 106s on t h e major t i s s u e s of

8 166 the body a r e being currently carried out by Hight who i s also determining the composition of the gain i n l i v e weight. A prelimiilary comparison between two breeds of sheep Cheviots and Romneys has been made (Kirton, Barton and Cresswell 1959). This work showed t h a t the carcasses of mature Cheviot ewes contained significantly more protein and water and t h i s was related t o t h e i r heavier, though stat i s t i c a l l y nonsignificant weight of dissectible muscular t i s s u e, The chemical and physical composition of 39 mature ewes which had been grazing two d i f f e r e n t perennial ryegrasses, each with and without white clover, have been studied ( U l y a t t 1960). Large differences i n c o q o s i t i o n between groups of animals grazing the different pasture types have been demonstrated. This material also allowed a study of the e f f e c t s of b i r t h rank (single and twin lambs born, l o s t lambs, and barrenness) on the ehemic a l and physical make up of the ewe carcass. There have been other projects of a minor nature i n recent years but s u f f i c i e n t has been discussed t o indicate t h e type of problems being investigated. The approach i s t o obtain, wherever possible, data t h a t w i l l have application not only i n t h e f i e l d of meat but also i n the f i e l d of body composition. This a t t i t u d e is adopted because it is believed t h a t knowledge of body composition i s of the utmost importance i n nearly a l l domestic animal experimentation and as yet t h i s area is s t i l l r e l a t i v e l y unexplored. LT CTED Barton, R.A. (1957). The problem of overfat meat. 1957, Massey Agricultural College, Sheepfarming Ann. Barton, R.A., and Kirton, A.H. (1956). Determination of f a t i n mutton carcasses by measurement of specific gravity. Nature (Lond.), 178 : 920 Barton, R.A., and Kirton, A.H. (1958a). Assessment of f a t i n mutton and lamb. Proc. N.Z. Soc. AnimT Prod., 18 : Barton, R. A., and Kirton, A.H. (1958b). Carcass weight a s an index of carcass components with p a r t i c z a r reference t o fat. J.Agric. Sci., 50 : Barton, R. A., and Kirton, A.H. (l958c).. The l e g and the l o i n as indices of t h e composition of New Zealazd lamb and mutton carcasses. N.Z. J. Agr i c. Res., 1 : Kirton, A. H., and a r t o n, R.A. (1958a). Live weight l o s s and i t s components i n Romney ewes subjectez t o Lthyroxine therapy and a low plane of nutrition. P a r t. Effects on l i v e weight, carcass weight and carcass composition, J. Agric. Sci., 3 : Part 11. Effects on some noncarcass components of l i v e weight. J. Agric. J. SCi 51 :

9 167 Kirton, A.H., and Barton, R.A. (1958k). Specific gravity as an index of *the f a t content of mutton carcasses and various j o i n t s. N.Z. J. Agr i c Res., 1 : Kirton, A.H., Barton, R.A., and Cresswell, E. (1959). A note on a comparison between the carcass composition of Romney and Cheviot mature ewes. N. Z. J. Agric. Res., : Kirton, A.H., U l y a t t, M.J., and Barton, R.A. (1959). The composition of some fatfyee carcasses and bodies of New Zealand sheep. Nature (L0nd.h 184 : Kirton, A.H., Barton, R. A., and Rae, A.L. (1960). The chemical composition of lamb carcasses: t h e efficiency of determination. (n preparation)., Kirton, A.H. and Barton, R.A. (1960). A study of some indices of the chemical composition of lamb carcasses. (n preparation) Palsson, H. (1939). Meat q u a l i t i e s i n the sheep with special reference t o the Scottish breeds and crosse8. J. Agric. Sci. 29 : Preston, T.R., and Gee,. (1957). Effect of hexoestrol on c a r c a s ~compos i t i o n and efficiency of foot u t i l i z a t i o n i n fattening lambs. Nature (bnd.), 179 : 247. M t h P i l l i n g, S. H., and Barton, R.A. (1954). Overfat ewe mutton is a s e r i ous problem. N.Z. J. Agr i C. 88 : U l y a t t, M.J. (1960). Body cosqposition studies of t h e New Zealand Romney ewe. Unpublished M.Agr.Sc. thesis, Massey Agricultural College Library. CHARMAN KEMP: Tbank ;you very much, Mr. Kirton Now, t o lead t h e discussion on these two papers we have Bo* Ramsey now of the University of Tennessee. Boyd. MR. RAMSEY: F i r s t, would l i k e t o express our thanks t o our Hew Zealand neighbors. would l i k e t o thank these people from a l l other countries who have been giving thought t o research on W e have heard them explain t h e grading of carcasses instead of grading after c h i l l i n g as we do. And the producers are paid fixed prices. t h i s subject. W e are sorry t o hear they, too, have a f a t problem. W e hoped maybe they might give us a solution t o similar problems that we have i n t h i s country. W e a l s o heard an explanation of the method of estimating composition.