Abstract
This study aimed at estimating genetic parameters and investigating genetic trend for new fineness index of marbling. Carcass data were obtained from Japanese Black cattle (n = 8,422) shipped to a meat processing plant in Hokkaido in September of 2005 to December of 2010. Digital images around the rib eye at the 6th and 7th rib section were taken and analyzed. Genetic analyses were conducted to estimate heritabilities for each image analysis trait and genetic correlations between new fineness index of marbling (NFI) and other image analysis traits using single/multiple trait animal models. The estimated heritability of NFI was 0.62. This indicates that NFI is available as genetic improvement trait. Genetic correlations between NFI and coarseness index of marbling or fineness index of marbling (conventional) were -0.01 and 0.60, so NFI is independent of coarseness index of marbling and correlated with conventional fineness index of marbling. Genetic correlations between NFI and marbling percent or BMS were 0.62 and 0.69, respectively. It was suggested that the improvement of BMS resulted in changing NFI for the better. Standardized predict breeding value (SPEV) of NFI and MP for dam increased since 1990. However, SPEV of these traits in 2005 were 0.9 and 1.4, respectively, the difference was 0.5 despite the high genetic correlation of NFI and MP. Thus, genetic improvement of NFI was inferior as compared with that of MP. The improvement with a focus on BMS results in an increase in coarseness marbling of rib eye area.
