MUSCLE BIOPSY INDEX FOR DISCRIMINATING BETWEEN ENDURANCE HORSES WITH DIFFERENT PERFORMANCE RECORDS

Biopsies were taken from three different depths of the gluteus medius muscle of 36 endurance horses aged between four and 17 years. Twenty o f the horses were considered excellent performers according to their t hree fastest records in endurance events over the previous two or thre e years. The other 16 horses were moderate performers, with a mean rac ing speed <3.5 ms(-1) (in 120 to 180 km endurance rides), <4.0 ms(-1) (in 80 to 120 km endurance rides) or <3.75 ms(-1) (in 40 to 60 km endu rance rides). The biopsy specimens were analysed for fibre type distri bution (type I, IIA and IIB), fibre area and relative fibre area. The activities of the enzymes citrate synthase, 3-hydroxy-acyl-CoA-dehydro genase and lactate dehydrogenase were also determined. The data were s ubjected to discriminant analysis and principal component analysis. It was possible to discriminate correctly between the horses according t o their performance records by means of the discriminant analyses when the histochemical and morphometric data from all three muscle biopsie s were used, but not when data from only a single muscle biopsy were u sed. Principal component analysis confirmed that the most efficient mu scle parameters describing the athletic potential of endurance horses were the percentages and relative areas of the fibre types. Horses wit h a better endurance performance had higher percentages and relative a reas of types I and IIA fibres and lower percentages and relative area s of type IIB fibres than moderate performers.