Muscle fibre type composition in young and racing Swedish cold-blooded trotters

Abstract

Fibre type composition of skeletal muscle in horses varies due to factors like breed, age and training. Variations due to these factors in muscle fibre type composition of the Swedish cold-blooded trotter, a heavier and slower breed than the Standardbred trotter, have not previously been reported. The objective of this study was therefore to investigate muscle fibre type composition of young and racing cold-blooded trotters using both histochemical and immunohistochemical methods. Muscle biopsies (gluteus medius) were obtained from 2-year-old (n ¼ 18) and 4-8-year-old horses (n ¼ 6). Four of the 2-year-old horses were sampled again during their 4-yearold season. All of the horses were in professional training and the group included superior racehorses. Fibre types (I, IIA and IIB) were visualized with the myosin ATPase technique. Some samples were also stained immunohistochemically to identify MHCI, MHCIIA and MHCIIX fibres using myosin heavy chain (MHC) antibodies. The oxidative capacity of the fibres was subjectively evaluated from NADH-tetrazolium reductase stains. Type I and type IIA fibres were all identified as MHCI and MHCIIA fibres, respectively, whereas type IIB fibre population included both pure MHCIIX and hybrid MHCIIAX fibres. The older racehorses had a higher proportion of type MHCIIA and a lower proportion of type MHCIIX fibres than the 2-year-old horses. Areas of type I fibres were larger and those of type IIB fibres were smaller in racing horses compared with young horses. The proportion of type MHCIIX fibres that stained medium for oxidative capacity increased with age and training. In conclusion, training and racing induce muscular adaptations in cold-blooded trotters as in other breeds. Furthermore, immunohistochemical methods detect hybrid fibres indicating that transitions of fibre types may occur.

Effects of training on equine muscle fibres and monocarboxylate transporters in young Coldblooded Trotters

“…The present study identifies changes in muscle fibre composition of young NSCT horses that are in agreement with the theory of fibre type transitions in a graded and orderly sequential manner from fast to slow with training (Pette 1998). Similar observations have been reported in a previous study of the same breed (Karlström et al . 2009), as well as in studies of Standardbreds (Ronéus et al .…”

“…To study this, a quantitative analysis of MCT1 and CD147 needs to be combined with the immunohistochemical analysis. Although the oxidative capacity can increase even in IIX fibres with training (Snow and Valberg 1994; Karlström et al . 2009), a previous study using Western blots did not reveal differences in the muscular contents of membrane MCT1 between moderately trained and older, race‐fit horses (Koho et al .…”

“…Identification of myosin isoforms was performed in all samples with the commercially available monoclonal antibodies (Mab) N2‐261 4 (MHC I + IIA) and A4‐74 4 (MHC IIA) (Karlström and Essén‐Gustavsson 2002; Karlström et al . 2009).…”

“…The Norwegian and Swedish horses belong to a breed called the Norwegian‐Swedish Coldblooded Trotter (NSCT) that has evolved from a rural carriage and riding horse. The maximal trotting speed of NSCTs is lower than that of Standardbreds (Uhlin 2007; Karlström et al . 2009), which have been bred purely for trotting for centuries.…”

“…With this method, myosin heavy chains (MHC) characteristic for the main fibre types I, IIA and IIX are stained (Rivero et al 1996). Since the introduction of immunohistochemical methods hybrid IIAX fibres have also been identified in equine muscles (Rivero et al 1996;Karlström and Essén-Gustavsson 2002;Karlström et al 2009).…”