Are Racehorses Inbred? (Answered!)

I recently attended a local horse race with a friend.

Not one of the large, high-stakes races. Just a small, local competition.

Still, the race interested me a ton — especially when it came to the animals.

They raced with such ease, and I wondered not only how they were trained but what their descendancy was like.

My friend told me that he had grown up around horse racing and thoroughbred breeding.

He told me that they are always inbred, and it is a very strict lineage.

I was shocked!

To be quite honest, I wasn’t sure that inbreeding among animals like that was legal.

The answer is yes, Thoroughbred racehorses are becoming increasingly inbred. Inbreeding has increased significantly in the past 45 years, with the greatest rise occurring in the past 15 or so years.

So, I began to do some research on the topic to see what I could find out.

Today, I’d like to present my findings. Here is the answer to the question: “Are racehorses actually inbred?”

 

Why have racehorses started to become more inbred?

Every Thoroughbred horse alive today is the descendent of three stallions and a larger selection of mares from 17th- and 18th-century England.

Since then, no horses outside this lineage have been permitted to enter the bloodline.

Recently, researchers looked into the genetic diversity at thousands of genetic markers across the entire genome in more than 10,000 Thoroughbred horses from all of the major breeding regions of the world.

This is how they discovered that inbreeding has increased significantly in the past 45 years, with the greatest rise occurring in the past 15 or so years.

Since the 17th century, Thoroughbred racehorse breeding has been extremely controlled.

Artificial insemination is not permitted, which means that breeding stallions must be moved across the globe in order to mate with several hundred mares per season.

Breeding pairs are usually chosen for their athletic ability and competitive nature.

This is one of the reasons that the breeding of Thoroughbreds is so tightly regulated.

Allowing unregulated horses to enter the breeding line would bring in hundreds of years of descendants with unknown athletic ability that could compromise a horse’s athletic integrity.

 

Isn’t inbreeding bad?

When it comes to horse racing, there are positives and negatives to inbreeding.

Thoroughbreds have been genetically adapted through inbreeding for one purpose: athletic performance.

By being highly selective about the racehorses that are permitted to breed into the Thoroughbred line, modern day racehorses are incredibly adapted to the demands of competition.

However, there are definitely negatives as well.

For example, a racehorse might not be well-adapted to conditions outside his wheelhouse — a sprinter vs. a distance horse, dirt vs. turf tracks — or he might have a certain reputation for characteristics some people might consider negative.

There has not been much selection of Thoroughbred horses for characteristics including cold tolerance — which is difficult considering the temperatures in some climates where horse racing is popular, like the United Kingdom.

Thoroughbred horses are also, of course, at greater risk for inherited issues and genetic mutation.

These mutations can have negative effects on the health and lifespan of the animal.

 

Can breeders get rid of the genetic mutations?

Because many genetic mutations are rare and recessive, it is hard to breed them out of a population.

As with humans, animals have two copies of each chromosome.

This means that as long as the animal has one normal chromosome without the genetic mutation, then the mutation will not have any ill effect on the animal’s health.

It is only if the animal has two copies of the genetically mutated chromosome that the animal will be poorly impacted.

Therefore, all animal populations — including Thoroughbred horses — will always carry some genetic mutations in their lineage.

However, inbreeding does increase the chances of the animal inheriting two copies of the negative variant, because more of the ancestors are likely to have the recessive gene.

This means that the only way to decrease the chances of a genetic mutation that negatively impacts a horse’s health is to cease inbreeding — which would come at the cost of superior competition performance.

 

Is this negligent?

Actually, no.

While there is a greater risk of a negative genetic mutation that can impact the horse’s health, Thoroughbred horse populations are surprisingly well off.

Also, since the lineage has been kept so tightly regulated, it is easy for researchers to track the negative genetic variants that are present in the population and account for them each breeding season.

Also, as breeders are knowingly inbreeding, they do strive for genetic diversity where they can.

They have aimed to combine superior athletic performance with low risk of genetic consequences and, with hundreds of years of trial and error, they have managed to do so relatively well.

Researchers have said recently that the Thoroughbred horse population is actually thriving and quite viable.

 

Why isn’t inbreeding illegal?

While inbreeding has come to have quite a negative connotation, it is still quite prevalent among animal breeding — not just with horses.

There are benefits to inbreeding, because breeders are better able to control the outcome of the offspring.

There are two different types of inbreeding among horses.

The first is close breeding, which means the mating of a father to its daughter, a mother to its son, or a brother to its sister.

This makes it likely that the two mating partners have half their genes in common, allowing for the other half of their genes to combine to create more genetic diversity.

The second type of inbreeding is called line breeding.

This means mating half-siblings, half-cousins, grandfather to granddaughter, cousin to cousin, or grandson to granddaughter.

This, of course, also allows for genetic diversity.

It keeps offspring related to an outstanding horse that has extremely desirable athletic characteristics.

It is considered less dangerous than close breeding because of the introduction of more new genes.

As you can see, while inbreeding can cause negative genetic impacts, breeders go to great lengths to ensure as much genetic diversity as possible to mitigate those effects where they can.

 

Who were the horses that began the Thoroughbred lineage?

The Thoroughbred originated in Great Britain and its genetic origin is Arabian.

The first stallions of the breed were the Byerly Turk, the Darley Arabian and the Godolphin Arabian.

They were mated to native sprinting mares.

The offspring are considered the first Thoroughbred.

 

Are racehorses required to be Thoroughbred?

Definitely not! Horses don’t have to be a Thoroughbred to race.

Many different horse breeds compete in sanctioned horse races, including Quarter horses, Arabians, Paints, and Standardbreds.

Matching horses in a test of speed is an ancient competition and it does not discriminate against any breed of horse.

There are some races, such as the Kentucky Derby, that require a horse to be Thoroughbred.

However, there is plenty of opportunity for horses that are not part of the lineage.

 

As you can see, Thoroughbred racehorses are very much inbred.

In fact, they must be in order to be considered Thoroughbred because the lineage is so strict.

The practice is not illegal, but it does definitely come with potential negative effects, such as genetic mutation that can decrease the life span and health of the horse.

However, there are also some benefits to inbreeding, including maximizing the athletic capabilities of all those in the lineage.

Of course, a racehorse doesn’t have to be Thoroughbred, so not ALL racehorses are inbred.