Fibre composition and capillary supply of the Gluteus medius muscle in resting Chilean criollo horses

Abstract

A study to analyze fibre composition and capillary supply of the Gluteus medius muscle of the Chilean criollo horse under resting conditions was carried out. Six adult (5-10 year old), clinically healthy Chilean criollo horses were sampled through a muscle biopsy technique during the period previous to the rodeo competition. Muscular biopsies were obtained from the left Gluteus medius at 6 cm of depth below the fascia. Muscle samples were serially sectioned and stained for myofibrilar ATP-ase and amylase-PAS, in order to identify types I, IIA and IIB fibres and to evaluate the fibre type distribution, the cross sectional area and capillary density.

The results showed that the Chilean criollo horse has a greater proportion of fast twitch type II fibres than type I, whereas type IIB fibres (42.5%) showed a slightly greater proportion than type IIA (39.0%), which suggests that this breed of horses is best adapted to muscular work of speed and resistance. The greatest frequency of type IIB fibres and the low capillary density (253 ± 26 capillaries/mm²) seem to demonstrate that these characteristics are associated to a loss of fitness due to a prolongued resting period to which the horses were subjected.