Dosage Explained: DI, CD and Chefs-de-Race
Dosage is a method of putting a number on something breeders have always assessed by eye: whether a pedigree leans towards speed or towards stamina. It works by scoring the influence of certain exceptional ancestors, called chefs-de-race, and reducing the result to a small set of figures.
Chefs-de-race
A chef-de-race is a stallion identified as an exceptional influence on the breed. Not every good sire qualifies. The designation is reserved for stallions judged to have shaped the breed's direction, and the list is maintained and occasionally added to rather than being open-ended.
Each chef-de-race is classified by aptitude, running from brilliant at the speed end through to professional at the stamina end, with intermediate, classic and solid between them. A chef may be assigned to one category or to two adjacent ones where his influence spans both.
These categories are the raw material of the whole system. Everything dosage produces flows from which chefs appear in a pedigree, where they appear, and what they were classified as.
How a pedigree is scored
Only chefs-de-race within the first four generations are counted, and their weighting reduces the further back they sit. A chef in the first generation carries the most weight, one in the second carries half as much, the third half again, and so on. The logic is that a close-up ancestor contributes more than a distant one.
Adding those weighted contributions across the five aptitude categories produces the Dosage Profile, a set of five numbers describing how the pedigree's chef-de-race influence is distributed from speed to stamina. Two figures are then derived from it.
Dosage Index and Centre of Distribution
Dosage Index (DI) is a ratio comparing the speed side of the profile against the stamina side. A higher DI indicates a speed-forward pedigree. A lower one indicates a more balanced or stamina-leaning profile. A DI of 1.00 means the two sides are evenly matched.
Centre of Distribution (CD) describes the same balance on a scale centred on zero, where positive values lean towards speed and negative values towards stamina. It is the average position of the pedigree's influence along the speed to stamina axis.
The two figures move together, since both are derived from the same profile. CD is often the more informative of the pair because it is less prone to being distorted by a single extreme value.
What dosage is used for
The most common use is distance assessment. A pedigree with a high DI and a strongly positive CD suggests a horse likely to be effective at shorter trips and possibly precocious. A low DI and negative CD suggests one likely to want further and to take longer to mature.
Dosage has also been used as a screening tool for classic distance races, where thresholds were applied to filter contenders unlikely to stay. Those thresholds held well enough to become widely quoted, then were broken often enough that they are now treated as guidance rather than a rule.
The limitations
Dosage is useful, and it is also narrow. Four criticisms are worth understanding before relying on it.
It only counts chefs-de-race. Most ancestors in a pedigree contribute nothing to the calculation. Two pedigrees can be very different and score identically.
The classifications are judgements. Deciding which stallions qualify as chefs, and which aptitude category they belong in, is expert opinion rather than measurement. Reasonable people disagree, and reclassification changes results retrospectively.
It is blind to the female side's depth. Dosage weights by generation, not by whether influence arrives through the sire or the dam, and it says nothing about family quality.
It describes influence, not the horse. A pedigree can indicate speed and produce a stayer. Dosage is a statement about inherited tendency, not a prediction.
Dosage in G1 Goldmine
Dosage appears in the platform as a summary rather than a raw table of numbers, with an AI-generated interpretation of what the profile actually indicates for a given horse or mating. That is a deliberate choice: the figures are only useful if you know how to read them, and a plain-English reading of the balance is more practical for most decisions than the profile itself.
It sits alongside the Aptitude Profile, which approaches the same question from the opposite direction. Where dosage infers likely aptitude from ancestral influence, the Aptitude Profile looks at what comparable stakes winners actually did, mapping the ages and distances at which they won. Reading a theoretical indication against an observed record is more informative than either on its own.