Association of Posthatch Muscle Growth with the Progression of Breast Muscle Myopathies

Avian skeletal muscle growth is comprised of distinct and precisely regulated periods of embryonic and posthatch muscle growth. Embryonic muscle fiber formation, hyperplasia, results from the proliferation, attachment of myoblasts, and subsequent fusion to form multinucleated myotubes. The myotubes will then develop into muscle fibers composed of numerous myofibrils. Myoblast withdraw from the cell cycle and no longer participate in muscle growth after the formation of the multinucleated myotubes. Posthatch muscle growth results from the enlargement, hypertrophy, of existing fibers through the proliferation and addition of nuclei from the satellite cells. Satellite cells will withdraw from the cell cycle after the growth phase and upon being stressed by factors resulting in muscle fiber damage will reactivate to repair muscle fiber specific damage. Myopathies like Wooden Breast have extensive muscle fiber damage from necrosis and are unable to repair the damaged myofibers despite the activation of the satellite cells. The necrosis of the existing muscle fibers and suppressed regeneration of the muscle fibers results in the replacement of muscle fibers with connective tissue. In addition to the breast muscle structural changes, meat quality will also be impacted. Effects on breast meat include but are not limited to: changes in water holding; reduction in protein levels; increased fat; and sensory quality impacts resulting in consumer based downgrades of the breast meat product.