Abstract
The objective of this study was to evaluate the feasibility of using the ultrasound technique
in the genetic improvement of young Japanese Black bulls. Ultrasonic scanning was undertaken at
approximately 11 months of age, between the 6th -7th and 12th-13th rib cross section on the left side in performance
test stock to obtain ultrasonic carcass traits of rib eye area (REA7/13), trapezius muscle thickness
(TMT), latissimus muscle thickness (LMT), rib thickness (RT), subcutaneous fat thickness (SFT), intermuscular
fat thickness (IMFT) and beef marbling score (BMS). Data were collected from 525 young Japanese Black
bulls at the Livestock Improvement Association of Miyazaki. Single trait analysis was conducted by applying
a mixed model that included a random effect for sire and fixed effects for testing year and season. Age at the
start of the performance test was included as a covariate. The variance components were estimated by the
residual maximum likelihood procedure and heritability was computed. Except BMS all ultrasonic carcass
traits had moderate heritabilities, ranging from 0.15 to 0.40. Selection based on the phenotypic values of these
ultrasonic traits should be effective for the genetic improvement of young Japanese Black bulls.
