A Study of Ultrasonic Probing Techniques for Swine Ii. Prediction of Carcass Yield From the Live Pig

In order to examine the effect of probe site and pig weight at probing on ultrasonic machine and operator accuracy, 227 pigs were probed for subcutaneous backfat thickness at 80, 90, 100 or 110 kg. Ultasonic probe sites were 5 cm off the midline on the midback at a point aligned with the root (B1) or the apex (B2) of the curve of the last rib. Loin sites were defined as 15 cm posterior to B1 (L1) or directly above the stifle joint of the hind leg (L2) of a pig standing normally. A third midback measurement was defined as for B1 but 6 cm off the midline (B3). The value of layer 2 or total backfat depth measurements at these five sites in predicting carcass dissectible fat and lean tissue content were examined. The best combinations of probe sites included L1 and either B1, with R2 of 0.41, 0.70, 0.72 and 0.78 or B2 with R2 of 0.38, 0.70, 0.71 and 0.76 for 80-, 90-, 100-, and 110-kg pigs, respectively, when total backfat was used to predict percent dissectible fat of carcass. These results indicate that carcass yield cannot be predicted adequately at 80 kg and that the optimum probe weight was between 90 and 100 kg. However, the additional expense associated with performance testing pigs at weights greater than 90 kg cannot presently be justified. The R2 for either B1 + L1 or B2 + L1 when fat depth of layer 2 was measured at 90 kg was 0.66. The greatest consistency between operators was observed when fat depth of layer 2 was measured.