deciding the distance
Muscle mass development in most animals is controlled by the myostatin gene.
In Thoroughbred horses, variations of this gene have been found to be highly predictive of race distance aptitude. This is because of its close link to speed and early skeletal muscle development.
Horses with two copies of the speed type myostatin gene variant (C:C) are best suited to fast, short-distance, sprint races (1,000-1,600m), while C:T horses compete favourably in middle-distance races (1,400-2,400m); and T:T horses have greater stamina (> 2,000m).
In the donkeys and zebras studied, only the T-type myostatin gene variant was detected, indicating that this was the ancestral wild gene type.
Analysis of the skeletal remains of the 12 most important stallions central to the development of the Thoroughbred breed, including Eclipse, an undefeated 18th-century British Thoroughbred, found that all of the historic stallions were T:T.