Thoroughbred Horses and Quantitative Genetics
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Thoroughbred Horses and Quantitative Genetics

Quantitative genetics uses complex methods to study the heritability of a trait. This article explains the underlying idea and gives an example in thoroughbred breeding.

The Inheritability of Speed

Racing and breeding thoroughbred race horses has become a multi-billion dollar business, which relies heavily on the notion that the speed of a horse is an inheritable trait. Running speed, however, is not a simple trait, such as the seed shape of a pea. Several genes and environmental factors, such as diet training and the jockey who rides the horse all contribute to the eventual speed of a mature racing horse.

Now the question is, can such a complex trait be studied and understood? Can the pedigree of a horse be a good predictor for speed? The answers to these questions turn out to be yes, at least partly. But to provide solid answers, new statistical procedures had to be developed, in order to analyze complex characteristics. This analysis of complex characteristics has become known as quantitative genetics.

The Underlying Logic

The mathematical methods used in quantitative genetics are rather imposing and complicated, but it is possible to grasp the underlying logic without having to study complex mathematics. Everybody is able to recognize family resemblance. People often talk about ‘inheriting’ the father’s height, or the mother’s intelligence, and so on. Well, it is this family resemblance that lies at the basis of the statistical methods that are used in quantitative genetics.

When genes affect a certain characteristic, related individuals resemble each other more than they resemble unrelated individuals. And within a group of related individuals, closely related ones should resemble each other more than distantly related ones. Through comparing individuals that are related in different degrees, can provide information about the extent to which genes influence a certain characteristic.

Applying Quantitative Genetics in Thoroughbred Breeding

Such a quantitative genetic analysis has been applied to the inheritance of racing speed in thoroughbred horses. In 1988, a man named Patrick Cunningham and his colleagues examined the records of over 30,000 race horses. Their reasoning was that, if genes influence racing success, the racing success of a horse should bear more resemblance to the success of its parents than to the success of unrelated horses.

When the racing records of thoroughbred horses were analyzed, it was found that a considerable amount of variation in track performance was due to genetic differences. So, racing speed is heritable. With the use of statistic methods, it is possible to estimate, to some degree, the track performance of a horse based on the performance of its relatives.


  • Bokor, A.; Blouin, C.; Langlois, B. & Stefler, J. (2010). Genetic parameters of racing merit of Thoroughbred horses in steeplechase races. Italian Journal of Animal Science. 4(3), pp. 43 – 45.
  • Cunningham, P. (1991). The genetics of thoroughbred horses. Scientific American 264(5), pp. 92–98.

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Comments (1)

Good article