Body length and ultrasonic fat thickness measurements were taken on 86 live pigs in order to find an optimal probing site for estimation of lean meat proportion. The next day pigs were slaughtered and measurements with the Hennessy Grading Probe (HGP) were made in order to estimate the lean meat proportion.

Fat thickness, 6 cm off the dorsal mid line, increased from a value of 9·5 mm at a site 4 cm cranial to the last rib, progressively through intermediate sites to a value of 12·4 mm, 22 cm cranial to the last rib. Fat thickness measurements at different sites (live pigs) were highly correlated with HGP fat thickness at the site between 3rd and 4th from last rib (3/4 LR) and estimated lean meat proportion (carcasses); correlations ranged from 0.80 to 0.89 and -071 to -0.85 respectively. The most accurate predictor of estimated lean meat proportion from the live pig measurements was the measurement at 18 cm cranial to the last rib. Measurement at the site half the distance between the occipital bone and the base of the tail (midpoint) was the second-best for estimated lean meat proportion.

Generally, this midpoint on live pigs was situated around the 3/4 LR on carcasses. However, the range was considerable. Half of the number of animals had a midpoint in the range of -2.5 to 2.5 cm from 3/4 LR. The site midpoint is easily located on the animal and the results of this study suggest that it can be used as an accurate predictor of estimated lean meat proportion. Therefore it can serve as the probing site for classification of live pigs.