Comparison of skeletal muscle characteristics in chicken bred for meat or egg production. I. Histopathological and electron microscopic examination.

A comparative histopathological and electron microscopic study based on selected skeletal muscle in layer-type and meat-type chickens was carried out to detect possible effects of selection for rapid growth and increased muscularity on muscle health. Disseminated fibre degeneration and other myopathological changes occurred more frequently in muscles of meat-type chickens than in layer-type chickens of the same age. The breast region of meat-type chickens--highly developed as a breeding aim--was particularly affected. Experimental exertion demonstrated the limited adaptability of skeletal muscle to psychomotor stress in meat-type chickens. Meat-type chickens showed a higher increase of histopathological muscular lesions after repeated wing exercise than layer-type chickens. Ultrastructural lesions caused by experimental exertion were classified as adaptive-reversible in layer-type chickens. As opposed to this, irreversible destruction of myofibrillar architecture in meat-type chickens are an indication for muscle ischaemia after exertion. Significant changes of structural, metabolic and functional parameters of skeletal muscle related to breeding aims in meat type chickens contribute to finding an explanation for their increased susceptibility to pathological reactions.