The evaluation of ultrasonic instruments used to measure the depth of back fat at P2 in live pigs, Feb 2004

The grading system for pork carcasses in Northern Ireland is reliant on the weight of the hot carcass and the depth of backfat 65 mm from the edge of the dorsal mid-line (P2). With consumers continually seeking leaner meat, pig producers are encouraged to breed leaner breeds and leaner animals within breeds. As the heritability value of backfat depth is high, this is achievable through genetic selection of breeding stock. Ultrasonic instruments therefore play a key role in the prediction of backfat depth on live pigs mainly for the purpose of selecting leaner animals for leaner pork production. They can also be used to predict the depth of backfat at the P2 position on live pigs and therefore can be used to estimate when pigs are ready for slaughter. In order to achieve efficient and optimal pig production the accuracy of ultrasonic instruments in the prediction of backfat depth on live pigs and the correlations with values attained in the factory is critical.

Two commonly used hand-held ultrasonic devices, the SFK Pig Scan-A-Mode backfat scanner (SFK) and the Meritronics A-Mode Pulse Echo scanner (Meritronics), were evaluated and compared to measurements taken in the factory using the Ulster and Optical probes and using a calliper to measure backfat depth after dissection on the chilled carcass. All methods were applied to a total of 120 pigs, 60 boars and 60 gilts.

It was found that the SFK, when used on live pigs was a good predictor of the depth of backfat measured on the carcass at P2 in the factory. The Meritronics probe however predicted significantly (P<0.001) lower depths of backfat at P2 (10.98 mm) than the Ulster and Optical probes (11.57 and 11.39 mm respectively) and the SFK ultrasonic probe (11.67 mm).

There were robust correlations between all types of measurement with the relationships between the Ulster and Optical (R2 = 0.886) and between the two ultrasonic instruments (R2 = 0.854) being the strongest. Gilts were found to be significantly fatter (P<0.01, average P2 difference = 1.2 mm) at a similar weight and age than boars and it was suggested that the ultrasonic instruments were more accurate at measuring the depth of backfat at P2 on gilts. There was, however, no significant interaction between the sex of the pig and outcome from the different probe types. The study also showed that the measurements taken by the factory with the Ulster probe were consistently accurate when compared to the Optical probe used by the Quality Assurance Division, DARD.