In The Netherlands a system has been developed for classification of live pigs based on lean meat proportion. Ultrasonic backfat thickness measurements were taken on 377 live pigs to assess the ability of the developed system for estimation of the lean meat proportion. The measurements were made at the sites mid point (half the distance from the occipital bone to the base of the tail), mid point –2·5 cm and mid point +2·5 cm, 5 cm off the dorsal mid line.

On the same day, these pigs were slaughtered and the lean meat proportions of the carcasses were estimated using the Hennessy Grading Probe (HGP). HGP measurements were taken between the third and fourth from last rib, 6 cm off the dorsal mid line on carcasses (3/4 LR). The day after slaughter, 88 left carcass sides were randomly chosen to be dissected according to a simplified European Union (EU) reference method.

From the fat thicknesses measured, the one at the site mid point on live pigs was the most accurate predictor for the EU lean meat proportion. The use of multiple site measurements, compared with a single site measurement, significantly reduced the residual standard deviation for the estimation of lean meat proportion.

The site mid point on live pigs differed in longitudinal as well as in dorsal-ventral direction from 3/4 LR on carcasses.

The results of this study suggest that multiple backfat thickness measurements on live pigs can be used for prediction of lean meat proportion with sufficient precision for practical use. Therefore, the developed system can serve as a classification system for live pigs.

Fat (and muscle) thickness measurements were carried out in five slaughterhouses on 174 selected carcasses to compare the Hennessy Grading Probe (HGP) with the Renco Lean-Meater (Renco) and Pie Medical ultrasonic devices for their ability to predict the lean meat proportion of pig carcasses. The day after selection, all left carcass sides were dissected according to the simplified European Union (EU) reference method. In addition 44 of these sides were further dissected according to the full EU reference method.

In a further set of slaughterhouses it was found impossible to measure fat thickness with the Renco and Pie Medical ultrasonic device due to extreme singeing of the carcasses. From the five slaughterhouses, between third and fourth from last rib, 6 cm off the dorsal mid line, observations on fat thickness with HGP and Pie Medical were similar but observations with Renco were significantly lower (F < 0·001). Correlations between fat thickness measurements taken with HGP, Renco and Pie Medical all exceeded 0·95.

In terms of residual standard deviations of prediction formulae, the HGP performed highly better than Renco or Pie Medical (23·7, 25·1 and 24·9 g/kg respectively). These results, together with practical problems, make the use of ultrasonic measurements under practical conditions at present less feasible than using the HGP.

Ultrasonic probe data were available on 199 crossbred pigs (98 females, 101 barrows). These animals were probed at approximately 30, 50, 70, 100 and 120 kg live weight with two probing instruments (Krautkramer USM2, Combison 310) at three sites along the back. The measurements were examined as predictors of the proportion of valuable cuts (part dissection) and estimated lean concentration (at 100 and 120 kg live weight).

The standard deviations for proportion of valuable cuts (after correcting for sex effects) were 24·8, 26·7, 23·4, 27·1 and 29·4 g/kg at 30, 50, 70, 100 and 120 kg. Residual s.d. for predicting proportion of valuable cuts from live weight and ultrasonic probes (Combison, quotient fat to muscle area) were 190, 20·9, 19·3, 213 and 19·6. For the USM2, the residual s.d.s were 19·2, 26·3, 19·9, 25·1 and 24·6. Thus the Combison probe provided a better prediction of proportion of valuable cuts. The standard deviations of estimated lean concentration as determined by a Fat-O-Meater reflectance probe were 28·9 and 39·3 at 100 and 120 kg live weight. The residual s.d.s from live weight and ultrasonic measurements were 15·4 and 19·2 for the Combison probe and 21·5 and 20·5 for the USM2 probe. If the estimated lean concentration is accepted as a selection objective the value of ultrasonic probes as criteria in selection indices will increase.