An estimation of the fibre type compostion of eleven skeletal muscles from New Zealand White rabbits between weaning and early maturity.

Fibre types in 11 skeletal muscles from New Zealand White rabbits were differentiated on the basis of histochemical staining reactions for Ca2+-adenosine triphosphatase (Ca2+ATPase) at pH 9-4, cytochrome oxidase, succinate dehydrogenase and L-glycerol-3-phosphate:menadione oxidoreductase activities. Using these enzyme reactions it was convenient to divide muscle fibres into three main categories in 'white' muscles and two in 'red' muscles. Between weaning and early maturity most muscles showed little change in fibre type composition, particularly when Ca2+-ATPase activity was used as the criterion. Many muscles showed an uneven distribution of fibre types in transverse sections; this was particularly so in the cases of longissimus, semitendinosus, soleus and semimembranosus proprius. The methods successful in resolving fibre types in mature muscles were not so capable of resolving fibre types in neonatal muscles.