Shape assessment and muscle score in beef cattle
Series: Agnote DAI-256 Edition: First edition Last updated: 21 Aug 2001
The shape of an animal or carcase can be evaluated in a number of ways. HOW shape is evaluated is the biggest determinant of the usefulness of the evaluation.
This Agnote defines the differences in types of shape evaluations and explains WHY one shape evaluation, ‘Muscle Score’, is a useful description of animal value.
One of the most common methods is to evaluate the shape of an animal or carcase, allowing fatness to play its full part in determining that shape. This method is commonly referred to as ‘conformation’. When this method of shape assessment is evaluated, results show that as ‘conformation’ score increases, fatness increases. Meat yield in the boning room consequently decreases. The conclusion drawn from these studies is that increasing conformation score is at best of little use (when fatness doesn’t vary greatly) and at worst detrimental to improved beef production (boning room yield).
It has been clearly shown in experiments that a score can be given independent of fatness. In Australia, this score is known as ‘muscle score’. Muscle score, unlike conformation, is a measure of shape without the influence of fatness. This is the important difference between conformation and muscle score. As with conformation, muscle score is an evaluation of the thickness (quantity), a three dimensional view of the whole body (see the Primefact on Muscle scoring beef cattle). As ‘muscle score’ increases, so too does meat yield. It has been shown that when carcases from animals of the same measured subcutaneous fat depth but different muscle scores are boned out to meat, fat and bone, the higher muscled-scored animal not only has more total meat but also has less total fat than the lower muscle-scored animal.
It has even been shown that selection for muscle score in bulls resulted in their progeny being not only higher in muscle score but also lower in both subcutaneous and total carcase fatness.
‘Butt Profile’ is a shape index developed by Ausmeat in Australia to describe the shape of a carcase butt. It is a two dimensional view of the carcase as seen from the side. As with conformation score it is significantly affected by carcase fatness. It is included in the Ausmeat Carcase Language.
Confusion of Terms
Unfortunately, all three of these ‘scores’ (conformation, butt profile and muscle score) have used the same scoring terminology, ‘A’ for a high score and ‘E’ for a low score. The inference is that they are all the same, but they are not the same.
Fat influences both conformation and butt profile, resulting in neither being of much use in determining animal or carcase value, over and above a measurement or assessment of fatness. Whereas muscle score, because it is evaluated independent of fatness, adds to the prediction of animal or carcase value over and above an assessment of fatness alone.
The difference between butt profile and muscle score
Butt profile is based on a two dimensional view of the carcase as seen from the side.
This shape is not adjusted for fatness and hence the fatter the carcase the more the convexity, and the higher the score.
Transposing the butt profile view onto a live animal, it is:
Live muscle score is the thickness and convexity of the animal, relative to its size, discounting for sub-cutaneous fat.
It is mainly based on a view of the hindquarter.
As seen on a carcase, muscle score is appraised as:
Discounting for subcutaneous fat:
- Butt shape is a two-dimensional evaluation.
- Carcase muscle score is a three-dimensional evaluation (it evaluates volume).
Butt profile and muscle score are totally different views of the animal.
- Butt profile is side view only and relies on convexity seen from the side (two-dimensional evaluation).
- Muscle score is back view and relies primarily on thickness (and hence volume) as seen from behind (three-dimensional evaluation).
- Muscle score discounts for fatness, butt profile does not.
It is important that the two shape evaluations not be confused, even though both use scores from A to E.
Live muscle scorers should not use Ausmeat Butt Profile to test their ability as muscle scorers because they are completely different evaluations of shape.
Butt profile is of little use in evaluating carcase worth.
Research results on live muscle score
Two major research projects were funded by NSW Agriculture and the Meat Research Council in 1988 and 1990 (Perry et al, 1993 (a)&(b)).
Both projects concluded that live muscle score in combination with an assessment of subcutaneous fat improved the prediction of saleable meat yield. The second project also showed that live muscle score was not being influenced by subcutaneous fat or inter-muscular fat (fat between the muscles).
For each increase in muscle score at the same live weight and fat depth, dressing percentage increased by 1.7%. Saleable meat yield percentage increased by 1.5 to 1.7 % and lean meat yield (denuded of fatness) increased by over 2%. In lightweight steers, this equated to 10–15% increase in value.
Tables 3 and 4 show how Fat score’ (link to fat score Agfact) and Muscle score influence the economically productive characteristics of dressing percentage and retail meat yield.
Dressing % = (Carcase weight ÷ live weight) x 100
Table 3. Dressing % changes due to muscle score and fat score
Table 3 shows that as fat score increases, dressing % increases as much of the extra fat remains on the carcase. This helps to explain why many livestock buyers, long after lean animals were preferred, continued to buy fatter animals as they were often judged on their aptitude as buyers, by dividing the price they paid for a live animal by the carcase weight.
Retail meat yield = (weight of saleable meat ÷ carcase weight) x 100
Table 4. Retail meat yield % changes due to muscle score and fat score
|Live Muscle Score|
Table 4 illustrates the problem with increasing fatness and decreasing yield. As well, muscle score’s influence on both dressing % (Table 3) and retail meat yield % (Table 4) is clearly evident.
Repeatability of muscle scores
One of the most often asked questions of a subjective appraisal system such as muscle score is ‘how repeatable is it between assessors, within assessors scoring the same animal twice, and the same animal over time as it matures and fattens?’.
Research studies in Australia on muscle score repeatability have shown that within and between experienced assessors, muscle scoring is quite repeatable.
More recent research work in NSW and South Australia indicates that muscle score can be a useful tool for describing store animals for their future performance as finished carcases.
Implications of increased muscling for the breeding herd
There is little sound scientific information on the correlated response to selection for muscling on other productive characteristics of beef production.
Research work in 1995 indicated no adverse relationship between growth rate and increased muscle when muscle selection was carried out in combination with weight selection. This research also showed no adverse reaction from using high-muscled bulls, of the same breed, on heifers for their first calf. The indications are that weight of calf is the culprit for increasing dystocia and not muscle shape.
In fact, there is some circumstantial evidence that moderate increases in muscularity in the female, which can often be accompanied by improved pelvic area dimensions, could in fact reduce dystocia levels.
The perception that more-muscular females are less productive in terms of milk production and fertility has yet to be proven. However, it does highlight the fact that singular selection for one trait is not advisable. It could be expected that extremes of muscularity will have an adverse impact on function.
Current level of muscling in the NSW beef herd
The graph below is an estimate of the distribution of muscling in the cattle herd of NSW. It was derived from a survey conducted by NSW Agriculture in 1989 (roughly 2,000 slaughter steers in the northern half of the State).
Female muscle scores would be, on average, about 2/3 of a muscle score lower than the steers.
This means that the present level of muscularity in the beef cattle herd averages D to C-, which is quite low. Obviously there is plenty of room to increase muscularity within the general cattle herd before extremes or even heavy muscularity (B+ to A) become common.
McKiernan, W.A. (1990) ‘New developments in live animal appraisal of meat quantity in beef cattle’. Proc. 8th. Conf. Aust. Assoc. Anim. Breed. and Genet. pp 447-50. Hamilton, New Zealand.
McKiernan, W.A. (1995) ‘Growth, Carcase Value and Body Measurements from High and Low Muscled Bulls’. M.Sc. Thesis, University of New South Wales.
McKiernan, W.A. and Robards, G.E. (1996) ‘The Repeatability of Muscle Score in Beef Animals Between Birth and Twenty Months of Age’. Proc. Aust. Soc. Anim. Prod. 21 : 151-54.
McKiernan, W.A. and Robards, G.E. (1997) ‘Growth Performance of Steers Sired By High and Low Muscle Scored Bulls’. Proc. Assoc. Advmt. Anim. Breed. Genet. Vol 12.
McKiernan, W.A., Hoffman, W., Barwick, S.A. and Johnston, D.J. (1998) ‘Feeder Steer Assessments that are Guides to Feedlot and Carcase Performance’. Proc. NSW Beef Products Conference, Armidale.
Perry, D. and McKiernan, W. A. (1994) ‘Growth and dressing percentage of well and average muscled Angus steers’. Proc. Aust. Soc. Anim. Prod. 20 : 349-50.
Perry, D., McKiernan, W.A. and Yeates, A.P. (1993a) ‘Muscle score: its usefulness in describing the potential yield of saleable meat from live steers and their carcases. Aust. J. Exp. Agr. 33 : 275-81.
Perry, D., Yeates, A.P. and McKiernan, W.A. (1993b) ‘Meat yield and subjective muscle scores in medium weight steers’. Aust. J. Exp. Agr. 33 : 825-31.
Author: Bill McKiernan