Abstract
The purpose of this study was to investigate the genetic relationships among growth traits, feed utilization traits, carcass grading traits and image analysis traits in the ribeye of Japanese Black steers. In this analysis, 1,492 Japanese Black steers in progeny testing were used. The growth traits consisted of 6 traits including body weight at the start of the fattening period (BWS), withers height at the start of the fattening period (WHS) and average daily gain in body weight during the fattening period (ADG). The feed utilization traits consisted of concentrate intake (CONINT), concentrate conversion ratio (CONRA), digestible crude protein conversion ratio (DCPRA), and total digestible nutrient conversion ratio (TDNRA). Carcass grading traits consisted of 6 traits such as beef marbling standard (BMS). Digital images of the carcass cross section were taken between the 6-7th rib with photography equipment. Six traits such as fat area ratio (FAR), overall coarseness of marbling (OCM) and fineness index of marbling particles (FIM) were calculated as image analysis traits in the ribeye. Genetic parameters for these traits were estimated using the AIREMLF90 program. Effects included in the model were station-year-season and birthplace as fixed effects, age at the beginning of the fattening period as a covariate and additive genetic and residual effects as random effects. Heritability estimates and genetic correlations were estimated using a single-trait animal model and a two-trait animal model, respectively. Heritability estimates for growth traits, feed utilization traits, and image analysis traits were 0.24∼0.58, 0.50∼0.53 and 0.08∼0.70, respectively. Genetic correlations (± SE) of BMS and FAR with growth traits and feed utilization traits were from −0.13 ± 0.10 to 0.16 ± 0.09 and from − 0.04 ± 0.09 to 0.17 ± 0.09, respectively. However, genetic correlations (± SE) of OCM and FIM with growth traits were from 0.17 ± 0.11 to 0.37 ± 0.09 and from − 0.29 ± 0.10 to 0.06 ± 0.11, respectively. Genetic correlations (± SE) of OCM with feed utilization traits were 0.41 ± 0.09, − 0.07 ± 0.11, − 0.14 ± 0.10 and − 0.16 ± 0.10 for CONINT, CONRA, DCPRA and TDNRA, respectively. Genetic correlations (± SE) of FIM with feed utilization traits were − 0.23 ± 0.10, 0.19 ± 0.11, 0.23 ± 0.11 and 0.25 ± 0.11 for the same traits. Therefore, it was suggested that animals with genetically large body size or good feed efficiencies tended to increase rough marbling particles and to decrease fine marbling particles in ribeye.
