Fibre type composition of the Gluteus medius in endurance horses with different performance records

Abstract

Biopsies from three different depths of the Gluteus medius muscle were obtained from 36 endurance horses, aged 8.42 ± 2.85 years and of both sexes. Twenty of the horses were considered excellent performers according to the mean speed of their three fastest records in endurance events, 2 or 3 years prior to the study. The other 16 horses were considered moderate performers. Significant differences in muscle fibre type composition were recorded. Excellent performers had a higher percentage of type I and type IIA fibres (high and low myosin adenosinetriphosphatase activity at pH 4.5, respectively. Also, they had and a lower percentage of type IIB fibres (moderate myosin adenosinetriphosphatase activity at pH 4.5), including both type IIB oxidative (moderate to high NADH-tetrazolium reductase activity) and IIB non-oxidative (low NADH-tetrazolium reductase activity). The differences in distribution of fibre types were more marked in the deeper parts when compared with the surface regions of muscle. The results show that fibre type proportions of the Gluteus medius muscle, are directly related to the athletic ability of the horse for endurance events.