Abstract
The article presents the results of a comparative study on muscle growth and development in bulls of different genotypes at 18 months of age. The aim was to evaluate the effect of breed and genotypic combinations on the formation of individual muscles and muscle groups relevant for meat productivity. The study involved purebred Simmental bulls and their first-generation hybrids. Three groups were formed: Group I - Simmental; Group II - ½ Simmental × ½ Red Steppe; Group III - ½ Simmental × ½ Black-and-Mottled. All animals were raised under identical feeding and management conditions until 18 months, followed by control slaughter and detailed dissection of the left half-carcasses. Muscles were identified according to the International Veterinary Anatomical Nomenclature and grouped based on anatomical and topographic features. Muscle development was assessed by the absolute mass of individual muscles and their complexes. Results showed that, regardless of genotype, the largest proportion of muscle mass was concentrated in the muscles of the spine, shoulder girdle, thoracic and pelvic limbs. However, pronounced intergroup differences were observed. The highest absolute mass values were recorded in bulls of Group III, which exceeded Groups I and II in the total mass of spinal, shoulder, thoracic, and pelvic limb muscles, as well as the overall mass of counted half-carcass muscles. These findings indicate a significant influence of genotype on muscle growth and development. The data confirm the practical value of specific breed combinations in beef production, as they promote more intensive muscle formation and increase meat productivity in young cattle.