COMPARISON OF TRANSVERSE AND LONGITUDINAL REAL-TIME ULTRASOUND SCANS FOR PREDICTION OF LEAN CUT YIELDS AND FAT-FREE LEAN CONTENT IN LIVE PIGS

Live animal real-time ultrasound scans and carcass measures were taken on 80 pigs comprising two sexes (42 barrows; 38 gilts) and two haloth ane genotypes (40 carriers and 40 negatives) that were slaughtered bet ween 108 and 148 kg live weight. Transverse scans (TRUS), at right ang les to the midline, were taken on right (RS) and left (LS) sides at th e last rib. Longitudinal scans(LON) were taken 6.5 cm off the midline immediately anterior (ANT) and posterior (PST) to the last rib on both the RS and LS. Longissimus muscle depth and area and backfat thicknes s over the longissimus muscle were measured on TRUS. Backfat thickness and longissimus muscle depth were measured at each end of the LON. Ba ckfat thickness and longissimus muscle measurements were taken at the 10th and last rib on the RS of the carcass. Carcasses were fabricated using standard techniques to establish lean cut yields and carcass-sof t tissue was chemically analyzed to determine fat-free lean contents. Stepwise regression analysis was performed to develop equations to pre dict the weights and percentages of lean cuts and fat-free lean. Fat a nd muscle measures taken from ultrasound scans were generally less acc urate than last rib carcass measures at predicting composition. There was little difference in R(2) for equations based on either TRUS or AN T/LON; however, PST/LON, generally, were less accurate than ANT/LON. C ombining measurements from more than one scan gave little improvement in R(2) compared with the best single scan. Estimates of sex bias for carcass composition prediction were small. Halothane genotype and carc ass lean content biases were detected; equations derived from the pool ed data tended to overestimate the lean content of negative pigs and f atter carcasses and underestimate the lean content of carrier animals and leaner carcasses.