Pattern of fibre type distribution within muscle fascicles of pigs (Sus scrofa domestica)

In order to determine breed differences in the fascicle structure of skeletal muscles, longissimus dorsi muscles (LD) and semimembranous muscles (SM), Duroc, Large White, German Landrace and Swedish Landrace boars were analyzed. Fibre type delineation was based on the method of myofibrillar ATPase staining. The fibres in a fascicle were divided into layers according to their relation to the perimysium. In each layer, the proportions of fibre types I, IIA and IIB were determined and normalized according to the fibre type proportion in the whole fascicle. Generally, a high proportion of IIB fibres on the periphery, a prevalence of type I and IIA in the layer below, and altered proportions of type I, IIA and IIB in layer 3 were found to be the main characteristics of the distribution of fibres in a porcine fascicle. Breed dissimilarity was established in the arrangement of fibre types, particularly in the first and third layer. The breeds that showed the highest proportions of type I and IIB fibres in LD and SM muscles were German Landrace and Swedish Landrace boars.