Use of serial ultrasound measures in the study of growth- and breed-related changes of ultrasonic measurements and relationship with carcass measurements in lean cattle breeds.

The growth and breed-related changes of rib and rump characteristics in lean beef cattle and the ability of ultrasound to predict carcass traits were investigated. Three hundred bulls from three breeds were scanned monthly (6-7 times) using real-time ultrasound with final scans taken <7 days prior to harvest. The rib and rump ultrasound measurements, except intramuscular fat content, increased (P<0.05) with live weight. Breed affected most of traits. The 12th rib ultrasound measurements showed a weak to high positive correlation (0.131 to 0.976, P>0.05 to P<0.001) with 12th rib measurements in the carcass. Regression equations developed with the ultrasound measurements, explained 97% of the variation in longissimus muscle area, 88% of the variation in fat thickness and 57% of the variation in intramuscular fat content. When last ultrasound scan measurements were excluded from prediction equations, the R(2) significantly decreased. Ultrasound measures "in vivo" are viable options for assessing carcass attributes of lean cattle.