Thoroughbred Family Tree

“What I am attempting is to prepare the reader for the conclusion that there is no conclusion to the study of pedigrees.” J. A. Estes, former editor of The Blood-Horse

Pedigree refers to a horse’s family tree, with its paternal ancestors–sire/father–on the top, and its maternal ancestors–dam/mother–on the bottom. A horse’s pedigree provides insight into its potential ability and value.

A few basic points to consider from among the numerous facts and attributes regarding a sire are number and size of foal crops; percentage of progeny that are starters, winners and stakes winners; type of horse the sire produces: turf or dirt, sprint or route; precociousness of his foals — does he produce better 2-year-old runners or do they develop more slowly?; and age of the sire — some people believe the horse’s ability to pass on desirable traits diminishes as he gets older.

As with a sire, there are many factors to consider with regard to a dam. Such factors to consider are racing and produce record of the female side, going back at least two generations; performance of her foals on the track — how many made it to the track and started? What was their race record, i.e., number of starts, wins and purse money earned? How long did they withstand training?; and number of full and/or half-siblings that have been stakes performers.

There are as many theories about pedigree as there are theories about how to make money in the stock market. For example, some pedigree consultants pay particular attention to in-breeding and out-crossing, while others elect to focus on the physical or performance characteristics of the horse. Because beliefs differ so greatly, you should be as familiar with as many as you can, and select those theories you find most appealing.


Inbreeding is the term utilized to describe breeding in which the same ancestor appears two or more times within the first four generations of pedigree. For example, if the same ancestor appears in the third generation and again in the fourth, the horse is referred to as being “inbred 3×4.” The significance of inbreeding is that the ancestor to whom the particular horse is inbred will have greater influence, thus emphasizing certain characteristics. Most believe it is radical for a horse to be inbred closer than 3×3.


Outcross breeding is the opposite of inbreeding in that there is no repeat presence within four or more generations. An outcross is believed to offer greater variety and avoid concentration of good and bad characteristics


SOURCE: Frank Mitchell, Nicking: proven formula fails more often than not, Mid-Atlantic Thoroughbred, February 2000

If it worked for them, it will work for me. That pretty much sums up nicking – the theory of copying the mating of a successful horse to produce another successful horse. Nicking theorists believe there is a benefit to the crossing of certain horses or sire lines and successful crosses can be repeated. The most popular nick in recent times has been the Mr. Prospector/Northern Dancer nick.

An example of the Mr. Prospector/Northern Dancer nick is Fusaichi Pegasus.

Explanation of Performance and Production Indexes

When you read through the Stakes Winners section of The Blood-Horse and the Stakes Results section of Thoroughbred Times, you will notice the performance summaries of stallions contain production indexes such as SI, AEI, CI, ComSI, etc. Below, these indexes and other performance and production indexes found in the above-mentioned publications as well as other publications are defined.

Racing Index (RI)

The RI is based on the average earnings per start of runners in North America. The RI is calculated by taking all foals born in a given year and determining that crop’s average earnings per start for each year that it raced. Colts and fillies are separated for the calculation. After five years of racing, a runner’s RI does not change, even if it continues to race. The average earnings per start for a crop for a given year is set at 1.00. A RI of 2.00 would have earned twice as much per start during a given year as a horse of the same sex, from the same crop with a RI of 1.00

Sire Index (SI)

An average of the RIs for all of the stallion’s foals that have started three or more times in North America.

Comparable Sire Index (ComSI)

The average of the RIs of progeny produced from mares bred to subject stallion, excluding foals by subject stallion.

Average Earnings Index (AEI)

An index of the lifetime earnings of a sire’s runners compared to the average of all runners in the same years; average earnings of all runners in a given year is set at 1.00.

Comparable Index (CI)

The average earnings of progeny produced by mares bred to one stallion when they were bred to other stallions.

Broodmare Sire Index (BSI)

An average of the RI of all foals out of the sire’s daughters that started at least three times. For BSI to be calculated, a broodmare


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