Item 1, Topic 1
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4.6.1 Current industry methods

At present both the beef and lamb industries rely on rudimentary tissue depth measurements to reflect the composition of a carcass. This is based upon the assumption that the depth of fat measured at one location will correlate with the amount of fat in the entire carcass. In the beef industry this fat depth is measured at the P8 site (on the rump). For MSA graded cattle, rib fat depth is also measured over the loin-eye muscle at the quartering point.

Figure 4.14 Measurement sites for P8 fat depth and rib fat depth in beef carcasses.

In the lamb industry tissue depth is measured at the GR site which is located 110mm from the mid-line over the 12th rib. This can be measured in millimetres using a GR knife, or it can be estimated by palpating the spinal processes in the lumbar region of the carcass which is then related to GR tissue depth as fat scores which are reported in GR increments of 5mm.

​ Figure 4.15 Measurement sites for GR tissue depth in lamb carcasses.

These measurements do have an association with whole carcass composition. Williams et al. (2018a, 2018b) demonstrated the capacity for either GR tissue depth combined with lamb hot carcass weight (figure 4.6.1a) or rib fat depth combined with beef hot carcass weight (figure 4.6.1b) to predict the percentage of fat in the carcass. In both cases there were strong associations, but there was also significant error.

Figure 4.16 Predicting carcass fat percentage measured by computed tomography from GR tissue depth and lamb carcass weight (on the left) and rib fat depth and beef carcass weight (on the right).