- Conformation as predictor of total yield and proportion of lean meat in sheep carcasses
|Last update: March 27, 2012 11:49:04 AM|
CONFORMATION AS PREDICTOR OF TOTAL YIELD AND PROPORTION OF LEAN MEAT IN SHEEP CARCASSES
P.G. Marais & E.M. van Tonder,
Grootfontein Agricultural College Middelburg CP 5900
Controversy about the value of conformation as a predictor of carcass composition has continued for many years. Reported results indicate that in many instances conformation is related to carcass composition. However, the degree of correlation is of such a low order that predictions based on conformation are subject to a considerable degree of error. Research workers have therefore tended to view conformation as an unimportant characteristic. On the other hand the South African meat industry, and especially the farmer, have traditionally accepted conformation as an indicator of commercial value and consequently paid more for animals considered to be superior according to this criterion.
There are a number of reasons why one type of conformation is preferred to another. The most important of these is the presumption that carcasses with an apparent better conformation have advantages in terms of lean meat content and proportions of higher priced cuts. Furthermore carcasses displaying the preferred conformational features may aesthetically be more desirable to traders or consumers. In view of these alleged advantages it is important to determine the significance of conformation as a predictor of carcass composition. The object of this paper is to review the information that has become available on the subject over the past five years.
Conformation is exclusively determined by visual appraisal. The different categories provided for in scales for judging conformation vary in number between countries as well as breed societies. Scales providing for five to 10 point intervals are most commonly being used.
IMPORTANCE OF CONFORMATION
Queries on the importance of conformation as an indicator of carcass composition have not triggered the dispute or generated the research effort in sheep as in beef cattle, probably because in sheep there is not such a wide variation in conformation types. Nevertheless, there is still uncertainty as to the emphasis that should be placed on conformation in sheep breeding programmes. The traditional belief in the importance of conformation, held by many people in the industry, is not supported by the poor correlations found between conformation and lean meat content in carcass evaluation experiments.
Measurements on the live animal such as length, height and circumference have shown very little relation to carcass composition. Linear measurements are, however, correlated with mass and therefore would be correlated to some extent with characteristics for which mass is a predictor. Many studies have shown that the present-day beef/mutton animal is generally smaller and more compact than formerly, but that this trend has not increased the proportion of lean in the carcass or changed its distribution. A reversal of the trend to taller and longer may also not result in any change in carcass composition or distribution of tissues.
Attempts to alter the shape or conformation of meat animals and to increase the muscle mass in those portions of the carcass that have greater economic value is a subject of controversy that has intrigued animal scientists. This is particularly so, because research has proved that the mass of a given muscle remains a constant proportion of the total muscle mass even though differences in apparent conformation may exist among animals.
Most sheep conformation studies have been carried out within the specific breeds without adjustment for equal levels of fatness. In general, the conclusion was arrived at, that Iambs which display good conformation tend to become fatter than those with poorer conformation but that little difference in muscle thickness or proportion of higher priced cuts occurs.
The accuracy with which adjustment for equal fatness is made is crucial in determining the value of conformation as a predictor of carcass lean content. This is because conformation and fatness are usually positively associated with one another while in turn these features are conversely related to leanness. The effect of fatness on the carcass fat: lean ratio is often pronounced when compared to the effect of lean on the lean: bone ratio with the result that imprecise adjustment to equal levels of fatness can easily obscure the relationship between leanness and conformation. For the very same reason, therefore, is it important to determine the value of conformation as a criterion of carcass composition, if it is to be used in practice where degree of fatness cannot be adequately controlled.
Carcass mass which may also influence the relationship between conformation and carcass composition can easily be accounted for in carcass evaluation studies and commercial situations as mass is nearly always assessed. Marked discrepancies are likely to occur when tissue mass and dimensions are taken into account but these would be limited when tissues are expressed as percentages of carcass mass.
The marginal advantage of conformation as a predictor of the amount of lean in a carcass appears to lie in the identification of differences in lean to bone ratio. An evaluation of breed differences, however indicates that breeds with better conformation do not necessarily have higher lean to bone ratios. From the information presented in Table 1 it is clear that Suffolk crosses, for example, despite their relatively low lean to bone ratios exposed good conformation while the Texel crosses which showed the highest lean to bone ratio did not have sufficiently high conformation scores to expose their advantage. Relationships of this nature are also evident in the work of Kempster & Cuthbertson (1977), involving commercial Iambs of different types. The Suffolk crossbred group had the second highest conformation score but the lowest lean to bone ratio. The poor relationship between conformation and lean to bone ratio between breeds of sheep may reflect differences in bone structure, as appears to be the case in cattle.
The minor differences between British sheep breeds in carcass lean content at equal fatness, despite selection over a long period of time for different conformation types, together with poor relationships within a breed, indicate that selection based on conformation is unlikely to be economically rewarding. It may be argued that relationships established in breeds, of any particular country should not necessarily be applicable to those of other countries. The fact remains however, that the results of these investigations cannot simply be ignored.
Although the conclusions derived from these research data have often been verified and supported by various other workers, this aspect will undoubtedly remain a topic of discussion for livestock and carcass show judges and participants.
KEMPSTER, A.J. & CUTHBERTSON, A. 1977. Anim. Prod. 25, 165.
KEMPSTER, A.J., CROSTON, D. & JONES, D.W. 1981 Anim Prod. 33, 39.
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