Muscle fibre type and size, and muscle capillary density in young double-muscled blue Belgian cattle.

Bovine muscle biopsies were analysed for fiber type and capillary density by the acid ATP-ase and amylase-PAS methods respectively. Samples obtained from Belgian blue double muscled (DM) calves were compared for their fibre type, size and vascularization with samples from Friesian (F) calves. The animals were sampled both at 2 and 7 months of age. Changes in histochemical composition occurring with ageing, independently of the breed, and differences related to the muscle sampled by comparing biopsies obtained from the longissimus dorsi (LD) and gluteobiceps (GB) muscles in animals of both breed were also investigated. Independently of age and muscle, fibre type I percentage and area were significantly higher in F than in DM muscles. Type IIa area was significantly larger in F than in DM, while fibre type IIb percentage and area were higher in DM. The number of capillaries/mm2 was significantly higher in F than in DM. Fibre type IIa and IIb percentage as well as the diameter of the three fibre types was significantly higher in the oldest animals. Finally, independently of age and breed, fibre type I and IIb percentages were significantly higher in LD but lower in GB. The results mainly demonstrated that Belgian blue DM muscles present a higher proportion of IIb fibres and a lower capillary supply than F muscles.