Heritabilities and genetic and phenotypic parameters for gluteus medius muscle fibre type composition, fibre size and capillaries in purebred Spanish horses

Abstract

Heritability and genetic correlation parameters for muscle fibre type composition, fibre size and capillaries of the gluteus medius muscle were estimated for purebred Spanish (Andalusian) horses using restricted maximum likelihood with an animal model. The data consisted of muscle biopsies (three samples per animal removed at different depths) from 4-year-old ( n=290) and older ( n=47, 8- to 23-year-old) purebred Spanish horses of both sexes (208 stallions and 129 mares). Heritabilities of muscle fibre type traits were moderate to low ( h 2=0.11 to 0.28). Heritabilities for type I fibres-related traits (fibre percentage, cross-sectional area and relative area, h 2=0.28±0.09, h 2=0.19±0.06 and h 2=0.23±0.09, respectively) were higher than those estimated for type II fibres-related traits ( h 2=0.11 to 0.17), but heritability for type IIX (fast glycolytic) fibre percentage was moderate ( h 2=0.25±0.09). Nevertheless, type I and type IIX fibre percentages were phenotypically ( r p=−0.86) and genetically ( r g=−0.36) negatively correlated. Both type I vs. type IIA and type IIA vs. type IIX were genetically negatively correlated ( r g=−0.48 and −0.85, respectively). Present data show that type I fibre-related traits are more heritable than type IIA and type IIX fibre properties. The phenotypic variability observed for these traits is largely explained by non-genetic factors (training, nutrition). As type I fibre percentage, cross-sectional area and relative area are directly correlated with success in endurance performance horses [Rivero et al., 1993; J. Appl. Physiol. 75:1758–1766], the inclusion of these traits in breeding programs of Andalusian horses could be of interest for early selection of appropriate sires and mares in order to improve the athletic endurance capacity of this breed.