Abstract
The Presence of Intrafiber Fat Droplets in Muscle Fiber Types and the Distribution and Size of these Fiber Types in Four Muscles of Japanese Black and Holstein Cattle Atsushi SUZUKI, Shyuichi OHWADA, and Hideo TAMATE Department of Animal Science, Faculty of Agriculture, Tohoku University, Sendai 980 The presence of intrafiber fat droplets in five fiber types of skeletal muscles and the difference in size of each fiber type and in fiber composition were studied in Japanese Black Cattle (three steers, 30-months old, weighing from 591 to 696kg) and Holstein Cattle (four steers, 20 and 26-months old, weighing from 428 to 576kg). Muscle samples were removed from the M. longissimus thoracis (M. longissimus dorsi), M. semitendinosus, M. serratus ventralis, and M. masseter. Cross sections were cut on a cryostat and reacted with NADH diaphorase, myosin ATPase at alkaline pH, and β-hydroxybutyrate dehydrogenase(β-HBD). Formalin-fixed sections were stained with Sudan black B. Some sections were extracted with acetone before staining for the demonstration of neutral fat. Neutral fat droplets were not observed in the type A fibers (red fiber) and type B fibers (white fiber), which reacted strongly for myosin ATPase and negatively or very weakly for β-HBD. The type C, D, and E fibers(red fiber), which reacted weakly for myosin ATPase and weakly to strongly for β-HBD, contained fine neutral fat droplets. These findings show that particular red fibers contain fine neutral fat droplets. The proportion of the number and cross-sectional area of the C and D fibers, suggestive of the content of intrafiber neutral fat in muscles, was much higher in the M. serratus ventralis than in the M. longissimus thoracis and was lowest in the M. semitendinosus. The M. masseter consisted only of the E fibers. The proportion of the number of B fibers tended to be somewhat higher in Japanese Black than in Holstein cattle, but this tendency was not noted in the other fiber types. In the M. longissimus thoracis, the proportion of the number of B fibers to the sum of the number of A and B fibers was higher in Japanese Black than in Holstein cattle. The B fibers of Japanese Black were larger in diameter than those of Holstein cattle, but similar differences were not noted in the other fiber types. The differences in numerical proportion and diameter of the B fibers suggest a difference in muscle between the two breeds.
