Changes in the metabolic and contractile characteristics of muscle in malecattle between 10 and 16 months of age

Samples of semitendinosus muscle from 28 male cattle (18 Salers and 10 Limo usins) were taken at 10 months (biopsy) and at 16 months of age (at slaught er). The animals had received the same diet and were slaughtered after the same duration of fattening. The activities of isocitrate dehydrogenase and lactate dehydrogenase were measured in the muscle samples. The five lactate dehydrogenase isoenzymes were separated by electrophoresis under non-denat uring conditions and assayed by densitometry. Fibres were identified by his tochemistry by myofibrillar ATPase and succinate dehydrogenase activities a s SO (slow oxidative), FOG (fast oxidative glycolytic) or FG (fast glycolyt ic), and by immunohistochemistry by their reaction to monoclonal antibodies specific to slow and fast myosin heavy chain reactions in I, IIC, IIA, IIA B and IIB type fibres. The isocitrate dehydrogenase activity was not modifi ed between 10 and 16 months of age; the lactate dehydrogenase activity decr eased and was correlated with an increase in the proportion of the H isozym e to the detriment of the proportion of the M form. This period was charact erized by an increase in fibre size, increased expression of MHC IIa, resul ting in more IIA fibres, less IIB fibres, and an increase in the percentage of type IIAB fibres, however the proportions of SO, FOG and FG, when analy sed statistically, were not modified between 10 and 16 months of age.