Inter-and Intra-breed Variation in the Fiber Type Composition of M. longissimus lumbrum and M. biceps femoris in Japanese Black, Japanese Brown, Holstein and F1 (Japanese Black×Holstein) Steers

Inter- and intra-breed variation in the fiber type composition of M. longissimus lumborum and M. biceps femoris in steers was examined on the biopsy materials. Fibers were divided into Type βR, αR and αW. Japanese Black (born in Ohita and Kagoshima prefecture) and Japanese Brown (Aso and Kikuchi, Kumamoto prefecture), Holstein and F1 (Japanese Black bull×Holstein cow) steers were used. In both muscles, the marked inter- and intfa-breed variation was observed on the percentages of Type βR and αW. fibers with those reciprocal changes. Of all breeds, the Ohita-Black showed the largest percentage of Type βR fibers and the Kagoshima-Black the second in each muscle. On the other hand, the muscles of the Holstein were characterized by containing Type βR fibers at the lowest frequency. The Brown occupied middle position between the Blacks and Holstein in the percentage distribution of Type βR fibers and showed the largest percentage of Type αR fibers in the biceps muscle compared with the others. From these results it was suggested that the Japanese natives substantially differ in their fiber type composition in the muscles from those of the Holstein and also exhibit inter-and intra-breed variation.