Comparison of Skeletal Muscle Characteristics in Chicken Bred for Meat or Egg Production: II. Histochemical and Morphometric Examination

Comparative histochemical and morphometric examinations of layer-type and meat-type chickens were carried out to detect the effects of growth selection on metabolic and structural characteristics of skeletal muscle. A combined histochemical method (NADHOX/mATPase) was used to compare the fibre type profiles of the supracoracoideus muscle in layer-type and meat-type chickens of the same age. A significantly higher percentage of glycolytic fibres was found in the line selected for rapid growth. Very similar results were obtained in studies comparing the supracoracoideus and flexor cruris medialis muscles of layer-type and meat-type chickens with approximately the same body weight. These results indicate that the oxidative capacity of skeletal muscle in meat-type chickens is significantly reduced by a lower proportion of oxidative fibres. The morphometric analysis demonstrates that selective changes of fibre diameters additionally reduce the oxidative capacity. Adverse effects on capillarity and oxygen supply are known to be connected with a reduced oxidative capacity of muscle tissue.