Dosage: speed versus stamina in the pedigree
The Dosage system looks back through a horse's first four generations and scores the influence of a fixed list of important sires, the chefs-de-race. Each one sits in one or more of five aptitude groups that run from pure speed to pure stamina: Brilliant, Intermediate, Classic, Solid and Professional. Add up those influences and you get a short set of figures.
Dosage Profile (DP)
The five group totals written out in order, for example DP = 8-6-10-2-0. Weight toward the left means speed and precocity. Weight toward the right means stamina and staying power.
Dosage Index (DI)
A single ratio of the speed side of the profile against the stamina side. A higher DI points to a faster, more sprint-leaning pedigree; a DI near or below 1.0 points to a staying one. As a rough guide, a DI much above 4 suggests a pedigree that may not want a classic distance. Treat it as a tendency, not a verdict.
Center of Distribution (CD)
A number between roughly +2 (all speed) and -2 (all stamina) that marks where the pedigree's balance point sits. It's the most compact summary of the profile you'll get.
Dosage describes an aptitude a horse inherits on paper, a leaning toward speed or stamina. It's one input among many, never a prediction. Plenty of horses outrun their pedigree, and plenty never reach it.
Coefficient of inbreeding (COI)
The coefficient of inbreeding measures how closely related a horse's sire and dam are. Written as a percentage, it estimates the chance that the two copies of a gene a horse carries are identical because they trace back to the same common ancestor on both sides of the pedigree.
- 0%: no shared ancestors within the generations examined.
- A few percent: normal for Thoroughbreds, whose studbook is closed and therefore carries some background relatedness.
- Higher values: the mark of deliberate line-breeding to concentrate a prized ancestor, which concentrates the rest of that ancestor's genes along with it.
The number depends on how many generations you count. A COI over five generations and one over ten will differ, so depth matters when you compare horses. TurfAtlas states the generation depth next to the figure.
Breeders treat COI as a trade-off. Line-breeding can reinforce a desirable ancestor's influence, but too much of it narrows genetic diversity. Like Dosage, it describes the pedigree rather than rates the horse: useful context, not a measure of ability.