Features of skeletal muscle structure in Cobb-500 cross chickens in certain periods of ontogenesis

The paper presents the microscopic organization of skeletal muscles using the example of the superficial pectoral muscle and quadriceps femoris in 1, 8, 20, and 35 day-old Cobb-500 broiler chickens. The selected development period correlates with the main stages of the broiler diet change. Studies have shown that the muscle fibers in both muscle groups studied are classified into large, medium and small by size. During development, from 1 to 35 days, their thickness index increases and becomes maximal in the superficial pectoral muscle. The sex differences are manifested in the fact that the thickness of the muscle fibers in roosters exceeds that of chickens. Bundles of muscle fibers of the first and second orders are thicker in the quadriceps femoris muscle than the superficial pectoral muscle on day 1 of ontogenesis, while the opposite pattern is observed from day 8 to 35 of growth. The endomysium and perimysium are characterized by a predominance of thickness in the superficial pectoral muscle over the quadriceps femoris from day 1 to day 8, however, the opposite situation was noted from day 20 to 35. Thus, the differentiation of the studied skeletal muscles is characterized by complex dynamics with changes in relative micromorphometric parameters in different periods of ontogenesis.