Morphology and histochemistry of muscle fiber types of skeletal muscle tissue of lambs during growth

Abstract

Morphological and histochemical methods were used to study the degree of development of myofibers of semitendinosus muscle of lambs aged from birth to the slaughter period. Based on NADH-TR and m-ATPase, after alkaline and acid preincubations, muscle fibers were classified as SO, FOG and FG types. At birth, slow oxidative (SO) myofibers were clearly distinguished from fast myofibers. FOG and FG myofibers were not clearly visualized. At weaning and slaughter, fast myofibers were clearly subdivided into FOG and FG types. At birth, ultrastructural examination revealed myofibers with different degrees of maturation and a great number of satellite cells. At weaning, the majority of myofibers presented a differentiated aspect. Myofibers with variable degrees of differentiation and satellite cells were still frequent. At slaughter, despite the majority of myofibers revealed a mature and hypertrophic pattern, a great number of immature muscle cells was observed. This observation seems to indicate that the rate of growth is still active