An evaluation of the Hennessy and Chong Fat Depth Indicator, and the Ulster Probe, for use in pig carcass classification and grading

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Abstract
The Hennessy and Chong Fat Depth Indicator and the Ulster Probe automatic recording instruments developed for measuring fat thickness were tested against the optical probe for use in pig carcass classification and grading.Fat thickness measurements were taken using each probe 60 mm from the dorsal mid-line over the m. longissimus at the positions of the 3rd/4th lumbar vertebrae, 3rd/4th last ribs and last rib on a total of 110 hot carcasses covering the range of market weights in Great Britain. The standard deviation of carcass lean proportion at equal carcass weight was 35·4 g/kg.The instruments differed little in the precision of carcass lean proportion prediction: residual standard deviation (g/kg) for the multiple regression with carcass weight and the best individual fat measurement for each probe were: last rib optical probe, 22·1; last rib Ulster Probe, 22·7; and 3rd/4th last rib Fat Depth Indicator, 21/6. Residual standard deviation (g/kg) for carcass lean proportion prediction from carcass weight and all three fat measurements in multiple regression were 21·3 optical probe, 21·3 Ulster Probe and 201 Fat Depth Indicator.Similar mean fat measurements were obtained from the optical probe and Fat Depth Indicator, and for these instruments, but to a lesser extent for the Ulster Probe, the regression relationships with each other and with fat thickness measurements taken on the cut surface of the cold carcass were also similar.The differences recorded in precision are unlikely to be sufficiently important to influence the choice of one probe rather than another.