Muscle Fiber Types of Gluteus Medius in the Colombian Creole Horse

Abstract

The skeletal muscle has several types of fibers that differ in structure, metabolism, and function. Fiber types determine the ability of horses to perform in various sports or work activities. Gluteus medius muscles of Colombian creole horses (CCHs) were sampled to determine their fiber types. Samples were processed using myosin adenosine triphosphatase (mATPase) and immunohistochemistry for fiber typing, myofibril electrophoresis for myosin heavy chain composition, and nicotinamide adenine dinucleotide diaphorase activity for oxidative capacity. The following fiber proportions were observed by immunohistochemistry (n = 7): 22.5 ± 3.7% type I, 33.6 ± 2.3% type IIA, 43.6 ± 4.4% type IIX, and 0.3 ± 0.2% hybrid I/IIA fibers. The results obtained by mATPase were comparable. Regarding the oxidative capacity, 20.1 ± 4.0% had a high oxidative reaction, 32.7 ± 6.1% an intermediate reaction, and 47.2 ± 7.4% a low oxidative reaction. Of these, the high and low capacity correlated with type I and IIX fibers, respectively. Myosin heavy chain composition experiments (n = 7) showed 22.2 ± 1.6% of type I, 30.4 ± 2.7% of type IIA, and 47.4 ± 2.3% of type IIX. These values are close to those published for Andalusian horses but differ from some reported for other breeds. Considering the high percentage of type IIX fibers and low to intermediate oxidative capacity, we conclude that the CCH is adapted to perform power exercise and moderate- to high-intensity anaerobic work with short to average duration. Therefore, training should be aimed at increasing aerobic capacity and endurance if these animals are required to perform long-length exercise.