Genetic parameters for marbling arrangement in the rib eye and their genetic trend in Japanese Black cattle

The purposes of this study were to estimate genetic parameters and genetic trends of arrangement and characteristics of marbling on different region in rib eye using by 4,598 Japanese Black cattle (steer : 3,485, heifer : 1,113) shipped to carcass market in Hokkaido. Digital images of the rib eye on carcass cross sections between the sixth and seventh ribs were taken with the mirror type photography equipment. These images were divided into four quadrants by the first and second inertia main axes. The following image analysis traits were calculated for each quadrant of the rib eye as well as the whole rib eye : marbling percent (MP), coarseness index of marbling particles (CIM), coarseness index of the largest marbling (CLM), fineness index of marbling (FIM), average luminance of lean (ALL) and average luminance of marbling (ALM). Standard deviations of the first to fourth quadrants for each image analysis trait were treated as arrangement score of each trait. Heritability estimates for arrangement score of MP (0.13) was the highest among those of other image analysis traits (0.02-0.08). Genetic correlations of arrangement score of MP with CIM and FIM of whole rib eye were 0.38 and -0.49, respectively. These results indicating that the marbling arrangement could be improved by decreasing coarseness and increasing fineness of marbling. For genetic trend, arrangement score of MP improved year by year, CIM of the fourth quadrant and that for FIM of the second and third quadrants degraded. Attentions would be needed for the image analysis traits of each quadrant in the rib eye for the effective genetic improvement of marbling.