Machine effects on accuracy of ultrasonic prediction of backfat and ribeyearea in beef bulls, steers and heifers

Pre-slaughter ultrasound and carcass measurements of ribeye area (REA) and backfat (FAT) were recorded on composite beef bulls (n = 60), heifers (n = 60) and steers (n = 60). Breed composition of the composite was: 0.44 Briti sh (Hereford, Angus and Shorthorn) 0.25 Charolais, 0.25 Simmental and 0.06 Limousin. The Aloka SSD-1100 (AL) and the Tokyo Keiki CS 3000 (TK) ultrasou nd machines were compared by evaluating the difference between ultrasound a nd carcass measurements (bias), and the standard error of prediction (SEP). AL underpredicted REA in all three sexes while TK overpredicted heifers an d steers and underpredicted bulls. Both machines were similar in accuracy a mong bulls for REA. For FAT AL underpredicted all three sexes while TK unde rpredicted heifers and had very small bias for bulls and steers. SEP for FA T were similar for both machines. Both machines underpredicted REA in large r muscled cattle and overpredicted in smaller-muscled cattle. Both machines also underpredicted FAT in fatter animals and overpredicted FAT in leaner animals. Machines were similar in accuracy among cattle with larger REA but differed significantly (P < 0.05) among smaller-muscled cattle. Machines w ere comparable in accuracy among animals of all FAT sizes. This study demon strates that there is an important relationship between machine and the siz e and depth of muscle and backfat, respectively, and consequently between m achine and sex, in accuracy of ultrasound prediction.