ACTIVITIES OF SELECTED AEROBIC AND ANAEROBIC ENZYMES IN THE GLUTEUS MEDIUS MUSCLE OF ENDURANCE HORSES WITH DIFFERENT PERFORMANCE RECORDS

Biopsies of the gluteus medius muscle were taken at three different de pths from 36 endurance horses aged 8.42 +/- 2.85 years and of both sex es. Twenty of the horses were considered to be excellent performers on the basis of the mean speed of their three fastest records in enduran ce events over the previous two or three years, whereas 16 were modera te performers. The biopsy samples were analysed for the activities of the enzymes citrate synthase (an indicator of citric acid cycle activi ty), 3-OH-acyl-CoA-dehydrogenase (an indicator of lipid oxidation) and lactate dehydrogenase (an indicator of anaerobic metabolism). The 20 excellent performers had higher activities of citrate synthase (P<0.00 1) and 3-OH-acyl-CoA-dehydrogenase (P<0.02) than the 16 moderate perfo rmers. The activities of citrate synthase and 3-OH-acyl-CoA-dehydrogen ase increased by 65 per cent and 75 per cent, respectively, and the ac tivity of lactate dehydrogenase decreased by 23 per cent in the sample s taken at successively greater depths. There was a strong linear rela tionship between the ratios of the activities of lactate dehydrogenase /citrate synthase and lactate dehydrogenase/3-OH-acyl-CoA-dehydrogenas e and the depth from which the samples were taken for both performance groups (P<0.001). The intercepts of the regression lines were higher in the moderate than in the excellent performers (P<0.001 and P<0.01 f or the two ratios), showing that the endurance horses with the better performance record had a greater aerobic capacity and a relatively low er anaerobic capacity in the gluteus medius muscle than the horses wit h a poorer record.