Järvsöfaks, a popular cold-blooded trotter in Scandinavia. © Don Wright
They belong to either one of two closely related and interconnected breeds of horse - the Norsk Kaldblodstraver (Norwegian Coldblood Trotter) and the Svensk Kallblodstravare (Swedish Coldblood Trotter).
Despite the research revealing large individual variations in muscular characteristics, it seems that the muscles of young, cold-blooded trotters have a relatively low aerobic combustion capacity, which may be a reason why members of the breed often have a late debut on the racetrack.
The findings have emerged from Tobias Revold's doctoral research, carried out in Scandinavia, in which he studied factors affecting the probability of good racing performances in young, cold-blooded trotters.
His thesis also describes the horses' muscular characteristics and how these can change as a result of training.
Revold studied 144 cold-blooded trotters born in 2005: the conditions in which they grew up, their size and the breeding index of their parents.
He found that the parents' breeding index was the factor that had the greatest effect on whether a young horse began racing and on its chances of performing well during the three-year season.
In addition, Revold took tissue samples of the horses' posterior pelvic muscle (musculus glutaeus medius) and analysed the composition of muscle fibre types, the blood supply to the muscles and the activity of major muscle enzymes.
His research showed that there were large individual variations in muscular characteristics among the horses in the trial, but that the oxidative capacity of the muscles - their aerobic combustion capacity - was generally lower among these horses than that previously seen in comparable breeds.
Revold also looked at how the muscular characteristics of eight cold-blooded trotters changed during a two-year training period and how lactate transporters were positioned in the muscle tissue of these horses.
Heredity is more important than environment in the performance of young cold-blooded trotters, researcher Tobias Revold has found.
The lactate transporter MCT1 was chiefly proven to be present in muscle fibre with a high oxidative capacity.
The research work was carried out at The Norwegian School of Veterinary Science and at The Swedish University of Agricultural Sciences.
Some analyses were also conducted at the University of Helsinki.
The thesis is entitled: "Performance predictors and muscle characteristics in young Norwegian-Swedish Cold-blooded Trotters".