Changes of marbling characteristics of the rib eye during fattening period and the effects of sire for them in Japanese Black cattle

Changes in amount, shape and arrangement of marbling in the rib eye of Japanese Black was investigated during fattening period. Commercial Japanese Black cattle (3,087 steer and 1,043 heifer) were used. Digital images of the rib eye were taken on carcass cross sections between the 6th and 7th ribs with mirror type photography equipment. These images were divided into four quadrants by inertia main axes. The following were calculated for each quadrant of the rib eye as well as the whole rib eye : marbling percent (MP), coarseness index of marbling particles, and fineness index of marbling. The peaks of MP from steer were recognized at 30 months except third quadrant, however, fineness of marbling for all quadrants were increasing after 31 months. In heifer, the peaks of MP of all quadrants and BMS were recognized at 30 and 32 months. Fineness of marbling of heifer revealed almost constant value for 27 to 32 months. Changes in image analysis traits by slaughter age were different among quadrants. Large increase of MP on the 1st quadrant which showed the smallest MP among four quadrants at 25 months was recognized in steer. Furthermore peaks of MP and BMS were different among sires.