Postnatal Morphological and Histochemical Type Differentiation of the Porcine Muscle Fibres

Abstract

Histological and histochemical detection of myosin ATPase, SDH and glycogen activity were used to study seven topographically and functionally different muscles of 23 Duroc pigs aged 2-4 hours, 7 days, and I, 3 and 6 months. The aim of the study was to find out whether type differentiation of muscle fibres (MFs) is detennined genetically or whether it is variable, and if so, in what ways, to what extent, and what is its relationship with "load myopathies", and to help answer the question of the "giant fibre", MF splitting, and of suitability of individual types of differentiation histochemical methods.Our findings indicated that muscle fibres of neonates were fully morphologically aJ)d adequately histochemically differentiated, with MFII predominating. In addition to the basic MF I and II types, the myosin ATPase reaction helped us differentiate also the intermediary IIC type with its MS, SS and SM subtypes converging to type I; in some muscles we were able to demonstrate the IIA and lIB types differentiated to a different extent. In the first month of life, muscles were differentiated in: I) muscles with a predominance of MF II, anaerobic (m. longissimus dorsi, m. triceps brachii, m. gracilis and m. semimembranosus), metabolically equipped for "load myopathies"; 2) muscles with a high to dominant proportion (45·70%) of oxidative MF I (m. tibialis cranialis, m. trapezius, m. stemomastoideus). No marked further conversion was found at the age of 3 months, and at the age of 6 months only a minimum conversion occurred. Deep zones of muscles belonging to group 1 muscles showed a higher relative ratio of MF I than the surface ones. Change in the proportion of MF I:MF II took place by gradual conversion of intermediary MFs IIC of their subtypes MS ~ SS ~ SM in type I.Detection of SDH activity did not allow an objective type differentiation of MFs in piglets younger than I month. The glycogen content was not always in correlation with an adequate MF type. In glycolytic muscles, completely isolated MF lIB, of the "giant fibre" type, affected by dystrophic changes were identified. No longitudinally split MFs were demonstrated.