Abstract
The degrees of heterosis on the carcass and image analysis traits were examined using Japanese Black (JB : n = 4,343), Holstein (HOL : n = 174), and their crossbred (F1 : n = 3,343) shipped to a meat processing plant in Hokkaido, Japan. The highest values among the three breeds for rib eye area and beef marbling standard number (BMS) were recognized in JB (56.5 cm2 and 5.09, respectively). Although the carcass weight of HOL was the heaviest (474.5 kg) in comparison with JB (443.1 kg) and F1 (450.0 kg), yield score and BMS of HOL were the lowest (69.44 and 2.29, respectively), as HOL had many lower values on the other carcass traits. Carcass traits of crossbred excluding subcutaneous fat thickness were intermediate between the purebreds. Least square means of BMS of JB, F1, and HOL were 5.09, 3.02 and 2.29, respectively. This indicates that the average parent heterosis of BMS was -18.3. However, the average parent heterosis of marbling area ratio that remarkably affects BMS was −0.7. These results indicate that the BMS of crossbred may be evaluated lower despite their marbling area ratio. This may be due to higher overall coarseness of marbling of F1 (12.96) when compared to those of both purebreds (JB : 11.61, HOL : 13.27). Thus the official graders may evaluate the BMS as a lower value in F1.
