Investigation of factors affecting beef marbling score for Japanese Black and Japanese Black×Holstein by computer image analysis

In this study, the tendencies of the carcass traits and image analysis traits by level of marbling percentage in rib eye were investigated. The following were calculated by computer image analysis as image analysis traits : marbling percent (MP), coarseness index of marbling (CIM), coarseness index of large 10 marbling particles (CIM 1-10), coarseness index of the largest marbling (CLM), fineness index of marbling particles (FIM), minor-major axis ratio and complexity of rib eye shape. Image analysis traits and carcass traits from Japanese Black (JB : n = 4,283) and Japanese Black×Holstein (JB×HOL : n = 3,315) were used. Data were classified into 10 levels according to the MP in 5% increments for each breed. MP less than 20% and greater than 60% were the lowest and highest levels, respectively. Least square means of BMS in MP under 20% and 20-25% levels were slightly lower on JB (1.95 and 2.02) than JB×HOL (2.00 and 2.05). In contrast, least square means of BMS were higher on JB than JB×HOL in the avobe-25% levels of MP. The difference of BMS between the breeds increased directly as the level of MP. BMS of JB×HOL had been evaluated lower than BMS of JB at the same MP, and that tendency came to be at a remarkably higher level of MP. In all levels of MP, least square means of CIM and CIM1-10 on JB were lower than JB×HOL, and those of FIM on JB were higher than JB×HOL. This indicated that JB had much finer marbling particles than JB×HOL at the same MP. This may prove to be a cause of the difference in least square means for BMS between breeds at the same MP level. Correlation coefficients of BMS with CIM1-10 and CLM for JB were significantly negative (P < 0.05-0.01) in the avobe-35% levels of MP. For JB×HOL, similar negative correlations of BMS were recognized in the 20%-55% levels of MP. Correlation coefficients of BMS with CIM1-10 and CLM increased directly as the level of MP for all breeds. These results indicated that the coarseness of marbling might have a negative effect on the BMS at a higher level of MP.