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what is dosage in horse racing

In light of the drugs scandal surrounding former Goldolphin trainer Mahmood Al Zarooni who, at the time of writing, has lodged an appeal against an eight-year ban imposed by the British Horse Racing Authority for administering anabolic steroids to racehorses in his charge, it’s probably worth stating that, throughout this article, the term “dosage” has nothing to do with the administration of drugs.

Dosage is, in fact, a technique for classifying the pedigrees of thoroughbred racehorses by type and, in doing so, for attempting to predict the “distance potential” of a horse and the ratio of speed to stamina in its pedigree. The technique was created by Lt. Col. J.J. Vuillier, a retired French military officer and pedigree authority of the early 20th century.


Vuillier examined the extended pedigrees of the best horses and discovered that very few sires appeared with any great frequency. He called these sires chefs-de-breed or, in English, “heads of breed”, as he believed they had profound influence on future generations.

Chefs-de-breed, of which there are currently over 200, including some familiar names, such as Habitat, Northern Dancer and Sadler’s Wells, can be divided into five categories of distance potential, namely Brilliant, Intermediate, Classic, Solid and Professional. The Brilliant and Professional categories represent highest speed and least stamina and vice versa, while Classic category represents the ideal, theoretical balance of speed and stamina.


Working on the assumption that the influence of a great-grandsire is half that of a grandsire, that of a grandsire is half that of a sire and so on, a chef-de-breed in the first generation is assigned 16 points, chefs-de-breed in the second generation are assigned 8 points, chefs-de-breed in the third generation are assigned 4 points and chefs-de-breed in the fourth generation are assigned 2 points.


However, some sires are chefs-de-breed in more than one category. Sadler’s Wells, for example, has an aptitudinal designation of Classic/Solid, or C/S, meaning that, for the purposes of dosage calculation, his assigned points are divided equally between those two categories. For instance, if Sadler’s Wells appears in the second generation of a pedigree, 4 points are added to both the Classic and Solid scores.

Dosage Profile

Dosage calculation yields three statistics, known as Dosage Profile (DP), Dosage Index (DI) and Centre of Distribution (CD). The Dosage Profile is a series of five numbers which indicates how many points a horse has inherited from chefs-de-breed in each category.  Dawn Approach, winner of the 2,000 Guineas in 2013, for example, has a Dosage Profile of 2-4-8-2-0 (16).

Dosage Index

The Dosage Index is a single numerical figure that represents the ratio of speed to stamina from the Dosage Profile or, in other words, whether a horse is innately orientated towards speed or stamina. The higher the Dosage Index, the “faster” the horse. Dawn Approach has a Dosage Index of 1.67 or one and two-thirds times as many speed points than stamina points. It’s interesting to note that none of the Derby winners since 1940 had a Dosage Index greater than 3.80, with an average of 1.52 so, from a dosage perspective, the son of New Approach would appear to have every chance of adding the Epsom Classic to his already impressive CV.

Centre of Distribution

The Centre of Distribution is a single numerical figure, between -2 (pure Professional) and +2 (pure Brilliant), which indicates the exact balancing point of a pedigree. A Centre of Distribution of 0.00 indicates that a horse has the same number of speed points as stamina points in its Dosage Profile. Dawn Approach has a Centre of Distribution of 0.38, which means that he has slightly more speed points than stamina points in his pedigree. However, this figure, too, compares favourably with an average of 0.07 for all the Derby winners since 1940.


Note that while a Dosage Index of 1.00 or a Centre of Distribution of 0.00, or both, represent the theoretical ideal balance of speed and stamina in a pedigree, they are no guarantee of performance on the racecourse.

However, dosage can be a useful tool for predicting the likely preferences of horses early in their careers, in maiden races, for example, where empirical evidence is unavailable. At a simple level, horses with a higher Dosage Profile value are typically better bred than those with lower values, while horses with high Dosage Index values are more likely to be precocious, early-season types.


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