Forty-four Japanese Black fattening steers from four groups, produced in four districts
and consisting of differing genetic backgrounds were slaughtered to examine the characteristic
differences in muscle fiber types at the 6th thoracic vertebra of the M. longissimus
thoracis (LT). The influence of percentage, diameter, and relative area of each muscle
fiber type on the carcass characteristics and some quantity and quality traits of
beef taken from LT, were also investigated. Significant differences in the characteristics
of the muscle fiber types were observed among the four groups, except for muscle fiber
diameter in the αR fiber, and the relative area of each αW fiber. For all steers,
the average percentages and diameters of each muscle fiber type, βR, αR and αW were
26.8, 18.5 and 54.7% and 51.4, 50.6 and 52.4 μm, respectively. The relative area of
each fiber type was similar to those of muscle fiber composition. αR Fiber content
had significant negative correlations with marbling score (p<0.05), intramuscular
fat content (p<0.05) and ultimate pH value (p<0.05). Significant correlations between
the diameter of each fiber type, and the quantity or quality traits of the meat were
not found, with the exception of red fiber types (βR and αR) and meat color a(∗) values
(p<0.05) which were positively correlated.