This paper comparatively examines the genotypic features of the development of muscle groups and individual muscles of the carcass of purebred Simmental bulls, and bulls crossbred with Simmentals: ½Simmental×½Red Steppe and ½Simmental×½Black and White bulls at the age of 18 months. It was found that in terms of the absolute mass of individual muscles of the spinal column, the highest level of parameters was characteristic of the bulls of group III, except for m. multifidus, where the biggest mass was shown by group I. The smallest mass, both of individual muscles, and in the group as a whole, was observed in crossbred bulls of group II. The analysis of the development of individual muscles of the shoulder girdle indicates that purebred bulls of group I exceeded the bulls in groups II and III in terms of the mass of m. brachiocephalicus, m. serratus ventralis, and m. pectoralis profundus. The bulls of group III were characterized by an advantage over the bulls of group II in the mass of m. pectoralis profundus, m. serratus ventralis, and m. brachiocephalicus. A comparative assessment of the development of individual muscles of the thoracic limb indicates that crossbred bulls of group III were distinguished by an advantage over the bulls of groups I and II. The differences in the mass of both individual muscles and between groups I and II were significant. A similar pattern of intergroup differences manifested itself in the development of both individual muscles and the pelvic limb as a whole.
