Three stallions imported into England around 1700 — the Darley Arabian, the Byerley Turk and the Godolphin Arabian — founded the breed's male lines. On the female side, every thoroughbred traces its bottom line back to one of a few dozen foundation mares.
The Australian researcher traced classic winners' dams back to 43 foundation mares and numbered the families by how many classic winners each had produced. Families 44–50 and separate American and colonial families were added later.
The number is the family; the letter is a sub-family within it, headed by a notable mare chosen in the 1950s. Lowe's claim that some families were "running families" and others "sire families" hasn't stood up — which is why it's better to judge a family by what it has actually won.
Mitochondrial DNA passes unchanged down the female line, so it can test the old records — and it found some horses don't match their recorded family. On the male side, the great majority of today's thoroughbreds trace back to the Darley Arabian.
A HorseBytes family line follows a horse’s bottom line – its dam, 2nd dam, 3rd dam and on back – to the earliest mare in the HorseBytes database, called the founder. Every mare descended from her through her daughters shares the family’s code, such as HB 12, and the line through one daughter is a branch, such as HB 12-c.
Each mare is linked to her own dam. The line is followed back until the database knows no earlier mare: she founds the family, and every mare on the way joins it. When a new mare’s line runs into an existing family, she joins that family.
A number is given once and kept for good, so HB 12 means the same family in every report, this year and next. The number is a label; the family line rating says how good the family is.
The letter is the founder’s daughter the line comes down through: HB 11-a, HB 11-b. Granddaughters keep their mother’s branch, so a family has only a handful of branches – most have one or two, the most any has is five.
Nucciolina founds HB 11. Her daughter Allara starts branch a, so Alruccaba, Alborada, Albanova, Alwilda and the Arc winner Alpinista are all HB 11-a; Alannya’s line is HB 11-b.
Each family is compared with every other family in the HorseBytes database. A rating of 77 means the family is stronger than 77% of family lines.
Black-type winners per lot of the family. Small families are pulled towards the average, so one lucky winner doesn’t make a family look great.
The very best winners count on top.
When a mare appears in an older and a newer sale, any new black-type winners listed under her show a family producing now – a family on the rise.
In the 1950s Bobinski and Zamoyski’s Family Tables of Racehorses went through each of the old families and marked off lettered sub-families, each headed by a notable mare chosen at any generation. That is why an old family can run to two dozen letters: a letter is not a daughter of the 1700s founder. HorseBytes does the same job nearer the present, with a fixed rule instead of a judgement.
| Bruce Lowe (1890s) | Bobinski & Zamoyski (1950s) | HorseBytes family lines | |
|---|---|---|---|
| Starts from | Around 43 foundation mares of the early 1700s | The same old families, split into lettered sub-families | The earliest mare in the HorseBytes database, usually born 1950s–80s |
| What the letter means | — | A notable mare chosen as the head of a sub-family, at any generation | A daughter of the founder: one fixed rule |
| How many families | About 50, plus American and colonial families | A few dozen sub-families in the biggest old families | Thousands, each a recent family a buyer pays for |
| Kept up to date? | Numbered in the 1890s; a few families added since | Fixed when printed (from the 1950s) | Rebuilt every time a new sale is added |
| Tells you how good the family is? | No: a label | No: a label | Yes: a 0–100 family line rating from its results |
| Shows a family on the rise? | No | No | Yes: new black-type winners since the mares' earlier pages |
| Best for | The history of the breed | Tracing distant relationships | Judging a yearling at today's sales |
On a phone, swipe the table sideways to see all three.
A family begins with mares born in living memory, whose influence still shows in a yearling. A mare of 1720 contributes almost nothing to a horse sold today.
Every sale added brings new mares, new winners and new branches, with no new edition to wait for.
The family line rating says how strong the family is now; an old code only says where it began.
New black-type winners in a family are spotted as they appear, so you can catch a line on the way up.
A branch is always a daughter of the founder, so the same horse always gets the same code – no one’s judgement about which mares deserve a sub-family.
Family lines rank sale lots, pick out dark horses, show which families suit each stallion, and let you search a sale by family.
They reach right back to the foundation mares, so they can show that two families are distant relatives where HorseBytes stops at its earliest mare; and they are a shared standard used the world over. HorseBytes links families that meet further back, but keeps each one’s own code and rating. The two work well side by side: one for history, one for judging a yearling.
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