Genetic parameter estimates of yearling live animal ultrasonic measurements in Brangus cattle.

The objective of this study was to estimate genetic parameters for real-time ultrasound measurements of longissimus muscle area (LMA), 12th rib backfat thickness (FT), percent intramuscular fat (IMF), and yearling weight (YW) for 1,299 yearling Brangus bulls and heifers. A single ultrasound technician performed all measurements. The number of observations was 1,298, 1,298, 1,215, and 1,170 for LMA, FT, IMF, and YW, respectively. Genetic parameters were estimated for each trait using single- and multiple-trait derivative-free restricted maximal likelihood. Fixed effects were contemporary group (defined as same sex, same age within six months, and same environment), and days of age as a covariate. Correlations were estimated from two-trait models. Heritabilities for LMA, FT, IMF, and YW were 0.31, 0.26, 0.16, and 0.53, respectively. Genetic correlations between LMA and FT, LMA and IMF, LMA and YW, FT and IMF, FT and YW, and IMF and YW were 0.09, 0.25, 0.44, 0.36, 0.42, and 0.31, respectively. Yearling live animal ultrasonic measurements can be used as a selection tool in breeding cattle for the improvement of carcass traits.