ULTRASONIC MEASUREMENTS OF BEEF BULLS IN PERFORMANCE-TESTING PROGRAMS
Fat thickness and longissimus muscle area were measured ultrasonically on 229 beef bulls on performance test. Charolais bulls were leaner than Hereford and Angus at both start and end of test and grew more quickly. Rate of gain on test was not related to initial age, weight or fat thickness, with partial correlations of.00,.22, and −.01, respectively, for Charolais, and.08,.06, and −.05, respectively, for Hereford. Rate of gain on test was not highly related to final fat thickness and longissimus muscle area nor to changes in fatness and muscle area during test, correlations with rate of gain being.14,.21,.06, and.02, respectively, for Charolais, and.15,.23,.22, and.12 for Hereford. Predicted retail yield gains per day on test were very closely related to liveweight gains on test, with correlations of.99 for both Charolais and Hereford. Fat thickness measurements do not appear to have any value if used to predict retail yield per day, but might have a value in identifying beef bulls that exceed acceptable fat thickness by the end of test.