Capillaries of muscle in red cell hypervolaemic versus normovolaemic Standardbred horses

Abstract

Capillary supply in the gluteus medius of red cell hypervolaemic and normovolaemic horses was investigated. Muscle biopsies were taken from 2 groups of 4–9‐year‐old stallions: 10 normovolaemic (NV, CV/bwt=78.1 ml/kg) and 10 hypervolaemic (HV, CV/bwt=112.6 ml/kg). The muscle biopsies were analysed for fibre type composition, fibre areas, capillary supply and enzyme activities. There were no differences between groups for fibre type composition, fibre areas or enzyme activities. Hypervolaemic horses were found to have a significantly lower capillary density (HV: 587 ± 62; NV: 661 ± 57 cap mm−2), capillarisation in relation to mean fibre area (HV: 1.59 ± 0.19, NV: 1.77 ± 0.16 μnr2 10−3) and especially capillarisation of type I fibres (HV: 1.87 ± 0.24; NV: 2.15 ± 0.26 μm−2 10−3). The lower capillarisation of hypervolaemic horses could be one factor affecting their racing performance. © 1995 EVJ Ltd