Comparative study of muscle fiber type composition in the middle gluteal muscle of andalusian, thoroughbred and arabian horses

Samples were taken from the right middle gluteal muscle of 25 Andalusian horses, 20 Thoroughbreds and 10 Arabian horses, all aged between 5-and 12-years-old and not involved in training. Histochemical analysis was carried out using myosin ATPase after acid preincubation (pH 4.4) and NADH-tr in order to determine the percentage of different fiber types. Statistical analysis showed highly significant differences (P<0.001) in the proportion of type 1 and type 2 fibers between breeds. The Thoroughbred was found to have a significantly higher proportion of type 2A fibers (P<0.001) than the other 2 breeds, although differences in the proportion of type 2B fibers in different breeds were not found to be statistically significant. The Andalusian horse was found to have a higher proportion of fast-twitch fibers of low oxidative capacity (type FT) than the other 2 breeds (P<0.001). These results not only confirm those obtained in previous studies of different breeds of horses, but highlight the histochemical differences in the skeletal muscle of breeds of great commercial and sporting interest in Spain.