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Analysis of results from the recent 2013 Royal Adelaide Show led steer on hoof and on hook competition provided evidence that Limousin has maintained its dressing percentage advantage over all other breeds, but also identified inconsistencies between ultra sound scan and abattoir carcase measurements, especially for eye muscle area.
Of the 180 entries, key breeds represented were Angus/Red Angus (40), Hereford/Poll Hereford (22), Murray Grey (22), Limousin (18), Shorthorn (17), Red Poll (13), Simmental (12), South Devon (10), Santa Gertrudis (9), Charolais (5), and Braunvieh (5). Other breeds were represented by less than 5 entries each.
Average dressing percentages (carcase weight measured at the abattoir divided by liveweight measured at the show) are listed below. Dressing percentages based on empty liveweight should be increased by about 3% (assuming 5% gut fill):
Interestingly, two Murray Grey entries were reported to have the highest and lowest dressing percentages of 66.5% and 52.5% respectively!
Ultra sound scan and direct measurements of rib and P8 fat, and of eye muscle area, are shown in the scatter plots to the right.
Each point on the graphs represents the combined scan/abattoir measurements for each animal. Ideally scan and abattoir measurements for each animal should be equal and appear on the diagonal line. Errors or inconsistencies in either or both measurements will cause a point to deviate from the line, with points above the line representing over-reading by ultra sound, under-reading at the abattoir, or a combination of both.
Rib fat measurements are distributed within about +/- 3mm of the line. Although P8 fat has a similar distribution, there is a slight bias to below the line (ie under-reading ultra sound scan, over-reading abattoir measurement, or a combination of both).
In two cases, P8 and Rib Fat scan measurements exceeded abattoir measurements by 200% (3mm scanned compared with 1mm measured in the abattoir). Where fat depths were greater, scan measurements deviated from abattoir measurements by typically less than 50%.
Eye muscle area measurements showed a significant bias to average about 8.5cm2 above the line, suggesting that either ultra sound scanning exaggerated eye muscle areas, abattoir measurements under-estimated the areas, or a combination of both. In general, scan measurements were confined to the range +18cm2 and -5cm2 of the abattoir measurements.
Generally most eye muscle area inconsistencies advantaged Angus on the hoof, although Santa Gertrudis with a smaller number of entries (9 compared with 40 Angus/Red Angus) had the largest average inconsistency. Angus/Red Angus scan areas exceeded abattoir measurements by an average of just over 11%; the greatest inconsistency was close to 36% (scanned 80cm2 but 59cm2 measured in the abattoir).
Santa Gertrudis scanned on average 12.9% greater than measured in the abattoir (greatest inconsistency was 28.8%), Charolais was on average 9.9% greater, Murray Grey 9.3% greater, Simmental 7.8% greater, Braunvieh 7.4% greater, Hereford 7% greater, Shorthorn 6.7% greater, Red Poll and South Devon 5.8% greater, and Limousin 5% greater.
Comments are welcome.
The review was initiated by a show committee member who argues that judging on the hoof should not be influenced by scan results because of the observed inconsistencies.
James (see below) suggests that inconsistencies should be expected because the measurement methods are different and also that shrinkage caused by loss of condition will occur between the show ring and abattoir. The results indicate that shrinkage in eye muscle area, if this is the principal cause of the inconsistencies, appears to be greatest in Santa Gertrudis and Angus and smallest in Limousin.
An alternative or additional explanation provided for the inconsistencies is that scan and abattoir measurements were made at slightly different positions on the carcase.
Finally, according to a NSW DPI article titled Objective measurement in beef cattle showring judging:
"Eye muscle area (EMA) can also be measured by ultrasound although not as accurately as subcutaneous fat, hence measurements on individuals need to be interpreted with caution if being used by judges. The EMA scan should be related to the fat-corrected liveweight."