study of ultrasonic probing techniques for swine. I. The effect of operator, machine and site

Ultrasonic probe data were available on 99 Lacombe gilts and 128 barrows. These animals were probed at approximately 80, 90, 100, or 110 kg by two operators, with three probes (Krautkramer USM2, Scanoprobe 731 A, Renco Lean-meater [L-M]) at three sites along the midback and two sites along the loin prior to slaughter. Measurements were recorded for both the second fat layer and for total fat depth. Averaged over operators, machines and sites total fat was 19.7, 20.0 and 19.6 mm for the USM2, 731A, and L-M, respectively. Total fat averaged over operators, machines and sites increased linearly from 17.5 mm at 80 kg to 22.8 mm at 110 kg. While the two operators were in close agreement (0.1 mm) when only the first two fat layers were measured, they diverged by 0.4 mm when total fat was measured. The two midback measurements that were made 5 cm off the midline differed by only 0.5 mm, but when measured 6 cm off the midline increased the difference by 2.1 mm. The two loin measurements differed by 1.6 mm, suggesting that the greatest source of error in the ultrasonic determination of backfat thickness would be associated with poor location of the loin probe sites. Key words: Swine, ultrasonic probes, machine comparison, site evaluation