PREDICTION OF LEAN YIELD IN YEARLING BULLS USING REAL-TIME ULTRASOUND

A study was undertaken to determine the repeatability and accuracy of ultrasound measurements taken on yearling bulls and to assess the valu e of these live measurements to predict lean yield. Ultrasonic fat dep th and 1. dorsi area were measured on 616 yearling bulls prior to slau ghter. Corresponding carcass measurements were obtained through the Ag riculture Canada Blue Tag Program. Carcass side lean (LEANYIELD) was e xtrapolated from the lean content of the seven-bone rib section from t he carcasses of 41 Angus and 41 Charolais bulls. Stepwise multiple reg ression used live (USFAT and USREA) measurements to predict LEANYIELD. Repeatability (SER) and accuracy (SEP) statistics for USFAT were 0.8 mm and 1.6 mm, respectively. The corresponding results for USREA were SER = 4.3 cm(2) and SEP = 7.8 cm(2). The ultrasound lean yield (USLEAN ) prediction equation was: USLEAN = 599.2 - (9.5 x USFAT) + (1.1 x USR EA); R(2) = 0.73, RSD = 17.9 g kg(-1). Results indicated that LEANYIEL D was predicted better by USLEAN (SEP = 18.0 g kg(-1)) than by BTLEAN (SEP = 22.6 g kg(-1)). Results from a second group of dissected bulls (n = 110) confirmed that ultrasound can predict LEANYIELD as effective ly as carcass measurements (SEP = 22.8 and 22.6 g kg(-1) for USLEAN AN D BTLEAN) in young breeding bulls in this study.