EVALUATION OF MACHINE, TECHNICIAN, AND INTERPRETER EFFECTS ON ULTRASONIC MEASURES OF BACKFAT AND LONGISSIMUS MUSCLE AREA IN BEEF-CATTLE

Before slaughter, 44 Hereford-sired steers were measured ultrasonicall y for backfat (UFAT)and longissimus muscle area (ULMA) between the 12t h and 13th ribs by three technicians (TECH) using two different machin es (MACH) on two consecutive days (DAY). Each TECH interpreted (INT) h is own images in addition to other TECH images. The absolute values of the difference between the 2 DAY's ultrasound measurements for ULMA ( \LMAR\)and UFAT (\FATR\) were analyzed with a model including fixed ef fects of MACH and TECH with a random effect of steer and all interacti ons. For both \LMAR\ and \FATR\, MACH x TECH was significant (P < .10) . Correlations between the 2 DAY's measurements ranged from .36 to .90 and .69 to .90 for ULMA and UFAT, respectively. Simple statistics to quickly evaluate TECH and MACH were developed. Root mean squared error s (RMSE) and error standard deviations (ESD) between repeated measurem ents ranged from 3.89 to 11.32 and 3.93 to 11.34 cm(2) for ULMA and .1 2 to .20 cm and .12 to .20 cm for UFAT, respectively. For accuracy, th e absolute values of the difference between the ultrasound and carcass measurement for fat (\FATD\) and longissimus muscle area (\LMAD\) wer e analyzed with a model accounting for fixed effects of DAY, TECH, and MACH and a random effect of steer with all higher-order interactions. For \LMAD\, TECH x MACH was a significant source of variation (P < .0 01). Also, a similar model was fit that included the fixed effects of TECH, MACH, and INT and a random effect of steer with all interactions . The MACH x INT interaction was found to be significant for \LMAD\ (P < .05). From this research, TECH and MACH differences do exist. Ultra sound is a valid means of measuring carcass traits in live steers if a ppropriate personnel and equipment are selected.