Pedigree & Thoroughbreds | How Breeding Impacts Horse Racing

Some horse racing bettors take a keen interest in the pedigree of horses as this can provide an insight to likely race winners. Most often these bettors are looking to find out which horses are classified as thoroughbreds.

The thoroughbred is a breed best known known for agility, speed and spirit; all suitable characteristics for horse racing. Thoroughbreds are recognised as distance runners or sprinters, and their form usually reflects what they have been bred to do.


What Is The Pedigree Of A Horse?

The pedigree of a horse is their family tree — as shown in all racecards with the Sire (Father) and Dam (Mother) included.

Horses don’t necessarily inherit traits from their parents, but when dealing with novice races where most horses are making their debuts, pedigree is one of the only items sports bettors have to go by.

The majority of horse racing is of the handicap variety, where racing bettors can base their selections around form and performance. Yet others opt to delve deeper into the pedigree of horses to identify strengths/weaknesses, in order to better predict their potential.


What Is A Thoroughbred Horse?

Originating in England, the thoroughbred is breed of horse developed for racing and jumping. They are outstanding for speed and stamina, and come from a combination of several other breeds of horses.

The term thoroughbred is often used incorrectly to mean purebred — but thoroughbreds are actually their own specific breed, registered in the General Stud Book of the English Jockey Club, or similar clubs in other countries.

Thoroughbreds can be characterised by specific attributes such as:

  • Delicate heads
  • Slim bodies
  • Broad chests
  • Short backs
  • Short leg bones
  • Sensitive and high-spirited
  • Usually bay, chestnut, brown, black, or grey.


Importance Of Size

In terms of raising a potential racehorse, size is a big consideration. Sprinters are generally well muscled, while stayers or distance runners tend to be smaller and slimmer.

Historically, thoroughbreds have steadily increased in size. The average height of a Thoroughbred in 1700 was about 13.3 hands high. By 1876 this had increased to 15.3. The average height of today’s thoroughbred is a little over 16 hands (64 inches, or 163 cm), weighing about 1,000 pounds (450 kg) at maturity.

Although there have been champion racehorses of every height, the most successful racehorses tend to be of average size. This is partly due to the fact that:

  • Larger horses mature more slowly, meaning that racing puts stress on their legs and feet — which predisposes them to lameness.
  • Smaller horses are at a disadvantage due to their shorter stride and tendency of getting bumped by other horses — especially in the starting gate



Studiers of the Pedigree are intrigued by the influence of the ‘X-chromosome’, and use records that go back generations to support their theories.

A well-known genetic theory is known as the ‘X-factor’ claims that some thoroughbred broodmares have a recessive gene which, when rarely matched to a carrying stallion, would produce foals with enormous sized hearts (2-3 times larger).

Indeed the large heart influences a horse’s growth and development, strength, stamina, endurance, and longevity; traits not only applicable to racing, but to a healthy life in general. Many large-hearted horses live long lives, to 30 or beyond. Some studies also suggest that intelligence is also carried on the X-chromosome.

But the mutation alone does not necessarily make a champion horse. There are probably many thoroughbreds with the recessive gene living common lives. A good racehorse requires exceptional training, soundness, the optimal upbringing, and the willingness to run races. Therefore merely observing the bloodline represents a more traditional, perhaps hopeful, approach to breeding a winning horse. Nowadays examining the DNA of horses to find good breeding stock is becoming common practice.


Modern Approaches To Breeding

Delving back too far in the pedigree becomes of limited value since it can be a poor guide to quality. After all, an ancestor five generations back contributes only 3% of an animal’s DNA today.

The Green Monkey racehorse is an example of the dangers of relying on bloodlines. In 2006 a two-year-old colt with an impeccable pedigree sold at auction for $16m. At the time, this was the highest price of a publicly auctioned thoroughbred. It ran just four times and failed to win once. But could the buyer have known better?

It is believed that focusing solely on what the direct parents achieved is of most significance. Breeders can also take things a step further and find out more information about the parents’ DNA.

Genetic Profiling

Companies such as Genetics Limited, founded in 2000, create genetic profiles of horses. They were the first in the world to offer DNA screening for racehorse performance.

Over the last decade the profiling has helped to identify markers linked to equine stamina, strength, respiratory system and energy use. It is said that these techniques are 75% better than conventional non-genetic methods for selecting potential winners from a group of horses. The tests indicate whether or not a horse is best suited as a sprinter, a long-distance athlete or something in between.


Tests can also reveal the level of inbreeding in a horse. Sometimes a degree of inbreeding, which is often associated with health problems, can be beneficial to racehorses.

Breeders use a form of inbreeding called “line-breeding” — a process where horses are bred to reproduce qualities more than once in their pedigree. The intention is to create other horses with features as similar as possible to the exceptional ones identified, by narrowing the pedigree to a few closely related lines of descent. It reduces variability. Line-breeding has produced many beautiful, athletic and exceptionally talented horses.

Close breedings not only bring out the good and desirable traits in a horse, but also some of the worst traits which might have been lying hidden for generations. This is the weakness of inbreeding and linebreeding — it sometimes produces an extreme, rare case. It is so important to research as much as possible about a certain stallion for example, to whom you are breeding the related mare.

Outside of Genetics

Aside from genetics & DNA, other elements still play a huge part on the race day. The training, nutrition, jockey and track conditions remain of great importance.

Geneticists estimate that DNA accounts for only 30-35% of a horse’s performance; so trainers are increasingly turning to experts specialising in gait and lameness. Patterns have indeed proved useful in spotting the causes of lameness and it’s now known, for example, that racehorses put extraordinary pressures on their legs and muscles when galloping and each limb has to support the equivalent of two and half times the animal’s body weight. In a 500kg animal, that’s 1.25 tonnes with every stride.

This kind of analysis helps to improve the performance and longevity of racehorses regardless of their genetics. In many ways such studies are equivalent to sport scientists with the objective of pushing the healthy human anatomy to it’s limits during exercise.


Applications Of Pedigree Analysis To Betting

The pedigree suggests a horse’s capability based on its genetics.

Very little is known about the potential of horses in maiden races, or horses debuting on a new surface. Markets tend to form odds based on on public news, gossip or speculation. There’s not there’s not much focus on the bloodline. So that’s where pedigree becomes of most use.

Historically the offspring of good sires achieve more than those of low or mediocre sires. Therefore if you know nothing more about an unraced or lightly-raced horse than the identity of its sire, you already know something of value.

Admittedly, pedigree data can be overwhelming and off-putting. But that alone could mean there’s a greater chance of using it to your advantage.

You can find horse pedigree data from:


Interesting Facts About Racehorses

  • A horse who hasn’t yet won a race is known as a “maiden”
  • Statistically, fewer than 50% of all racehorses ever win a race. Less than 1% ever win a stakes race such as the Epsom Derby.
  • Horses that retire from a racing career and are not suitable for breeding purposes often become riding horses or other equine companions. Agencies exist to help make the transition from the racetrack to another career, or to help find retirement homes for ex-racehorses.


This article was originally written in 2016 and was updated for 2022.

Toby @ Punter2Pro
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ed pierce
ed pierce
7 years ago

I have heard from a lot of punters that science can’t accurately predict a good horse those are usually the people betting and losing. The science of choosing a good horse makes sense and it is backed up by facts that can’t be ignored. I will always look at a horse this way, especially if I am putting my money on it.

Reply to  ed pierce
7 years ago

More and more bettors are starting to look at Pedigree as a way of predicting races. Obviously if everyone did this then the odds begin to reflect the chance of the horse winning, and it’s worthless. However, i think that there are special cases where, for example, the horse isn’t experienced but has a particularly good bloodline. This type of scenario is an area that can definitely be explored for opportunities.