Abstract: To explore the characteristics of Mongolian horse skeletal muscle in terms of movement and meat quality, 52 pieces of major skeletal muscle (2×26 pieces) of 2 5-year-old healthy untaught adult stallions were selected as the research objects. Paraffin sections, immunohistochemistry and HE staining were used to obtain skeletal muscle morphology, fast and slow muscle fiber distribution, and average cross-sectional area of muscle fibers of 26 sites. Due to the differences of skeletal muscles at different parts, the muscle tissue was divided into 5 groups (head and neck, forelimbs, trunk, abdominal wall side and hind limbs) for statistics. The corresponding 24 parts were compared with the thoroughpure breds skeletal muscle obtained in the previous studies in the proportion of fast and slow muscle fibers.The results showed that the phenotype spectrum of the main skeletal muscles of Mongolian horses. Among them, the proportion of slow muscle fibers in cervical serratus, supraspinatus, biceps, wrist radial flexor, gastrocnemius, rhomboid muscle and thoracoventrlateral serratus muscle was relatively low. The proportion of slow muscle fibers in wrist radial extensors, triceps brachia, longest dorsal muscle and gluteus mesoamericas accounted for more than 70%; the proportion of slow muscle fibers was negatively correlated with the cross-sectional area of muscle fibers. The proportion of slow muscle fibers in Mongolian horse skeletal muscle was basically higher than that in thoroughpure, the difference in forelimbs and trunks were very significant (P<0.01), and the differences in hindlimbs and abdominal wall side were significant (P<0.05). Among them, the difference of the proportion of slow muscle fibers between Mongolian horses and thoroughbred horses in brachial triceps, longest dorsal muscle, gluteus medius and semimembranous muscle were greater than 50%. The results indicate that serratus equinagia, supraspinatus, biceps brachia, flexor carpal radial, gastrocnemius, rhomboid and thoracoventral serratus muscle have the potential for endurance training. The wrist radial extensors, triceps brachia, longus dorsius and gluteus medius have good quality and can be the focus of horse meat development; and the triceps arm, dorsal maximus, gluteus medius and semimembranous muscles can be used as the key muscles of horse athletic performance testing. These results provides a theoretical basis for Mongolian horse sports training and meat quality development.

Key words: Mongolian horse, skeletal muscle, muscle fiber type