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The GR (total tissue thickness at the twelfth rib, 110 mm from the midline) was measured with the AUS-MEAT sheep probe (ASP) on lamb carcasses at chain speed by an abattoir operator in two experiments, both at the same abattoir. In both experiments, GR was also measured on the carcass by an independent operator using a GR knife. For experiment 1, a total of 779 lamb carcasses were measured over four occasions and for experiment 2 data on 607 lamb carcasses were obtained on two occasions, twelve months after experiment 1. In both experiments, one operator measured the manual GR and a different operator used the ASP. A new version of the ASP was used in the second experiment. In only 30% of cases in experiment 1 did the operator probe at the correct rib, and in the majority of cases the thirteenth rib was used as the probing site. In only a small percentage of cases (2%) was the operator more than one rib away from the twelfth rib. In 67% of the cases for experiment 1, the operator probed at the correct site with respect to distance from the midline. Models were developed to describe the relationship between the manual and ASP GR measurements. In experiment 2, the amount of variation in manual GR explained by ASP measurements was greater than that in experiment 1 ( R 2 = 0·80 compared with 0·72), and the accuracy of the estimates was significantly increased (± 1·54 mm compared with 2·31 mm). The better over-all performance of the ASP in the second experiments was indicated by the fact that for 90% of the sample the ASP measurements were within ±2 mm of the manual GR measurements whereas, for experiment 1, the level was less than 70%. Measurement time (day), which could be described as an operator ‘effect’, was identified as an important factor influencing the accuracy of GR estimates but location of the probed site with respect to the GR site was not found important. The significance of operator training and monitoring is discussed on the basis of the results, as are the implications of the findings for objective purchasing systems. |
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