HISTOCHEMISTRY AND BIOCHEMICAL CHARACTERI STICS OF GLUTEUS-MEDIUS MUSCLE-FIBERS IN DRAFT HORSES OF THE EQUINE SUPPORT PLAN

Biopsies of the Gluteus medius muscle were taken at 3, 6, and 9 cm of depth in 16 inactive male and female draught horses of the equine supp ort plan, with ages ranging between 5 and 15 years old. The biopsies w ere analized by the histochemical techniques myosin ATPasa, to determi ne the fibrilar composition, area and least diameter, and the NADH-TR technique to determine the oxidative capacity of the fibres. Also, the activity of the citrate sintetase (CS), lactate deshidrogenase (LDH) and creatine phosphokinase (CK) enzymes were determined.The average va lues in relation with the percentage of each fibre type were 33%, 28%, 17% and 22% for the fibres type I, IIA, IIB oxidative and IIB nonoxid ative, respectively. The average area of the fibres was 3959, 4823 and 7087 mu m(2) and the average minimum diameter was 47, 52 and 59 mu m for fibres type I, IIA, IIB respectively. The average of the activity of the enzymes CK, LDH and CS was 0.484, 0.337 and 671 mu mol/min/mg p rotein respectively, showing an increase of the activity of CS with th e depth of the biopsy. This increase is related with the percentage of fibres type I. Results obtained show that Chilean mixed draught horse s have a high aerobic capacity and relative low anaerobic capacity in the Gluteus medius muscle. These muscle characteristics are consistent with the sort of work carried out by these animals: prolonged and sus tained exercise of low intensity.