FAQ Other Tips

Appendix Quarter Horses: A Winning Combination

Appendix quarter horse
Written by Aimee B.

The best of both worlds

In life, some things just go really well together. So well, in fact, that you hardly ever think of one without the other. A few examples? Peanut butter and jelly. Netflix and chill. Quarter Horses and Thoroughbreds.

The history of the Appendix Quarter Horse is, in part, a story about two breeds that just go really well together. It’s not a drama-free story, as many people have disagreed with introducing Thoroughbreds into American Quarter Horse bloodlines. Without those who believed in the best of both worlds, though, we wouldn’t have the Appendix Quarter Horse. Keep reading to learn more about this breed’s history, characteristics, and strengths.

What is an Appendix Horse?

Controversy surrounded the combination of these two unique breeds initially, and continues to this day. To make matters more complicated, there are actually two different breed registries for the Appendix horse.

Depending on which you consult, the definition even differs slightly. The two registries are the American Quarter Horse Association (AQHA) and the American Appendix Horse Association (AAHA).

Want to see an Appendix in action?

The History of the Quarter Horse

If you think of the American Quarter Horse, I’m willing to bet that you conjure up visions of cowboys riding the open range, roping cattle, and branding calves.

But according to AQHA, the breed’s origins actually began with American Colonists in the early 1600s and started not with ranching but with racing.

Entertainment was limited before the age of the Internet and the work was physically taxing. Colonists used horses they brought over from England for both fieldwork and transportation.

It wasn’t long before the Colonists developed a fascination with speed and began racing their horses along short stretches of road.

At some point, the colonists noticed that the horses belonging to a Native American tribe called the Chickasaw were much faster than their own.

These horses had been brought over by Spanish explorers and had both Spanish and North African Barb bloodlines.

The cross between the English horses and Spanish Barbs eventually became known as the “Celebrated American Quarter Running Horse” due to their speed at the most common race length–a quarter-mile.

Back in England, horse racing was also a popular pastime, only the distances were longer, ranging up to 4 miles.

Ever the enterprising thinkers, the Colonists soon looked to improve upon their own horses and increase speed over a longer distance.

Little did they know that introducing a new horse breed to their current breeding programs would forever change what is known today as the American Quarter Horse.

Appendix QH

The next breed introduced into the “Celebrated American Quarter Running Horse” at this point in history was the Arabian. In the early to mid-1700s, a stallion known as the Godolphin Arabian changed the English racing game.

This particular stallion would eventually become one of three foundation stallions for the Thoroughbred breed. In 1752, a Colonist named John Randolph imported a grandson of the Godolphin Arabian named Janus to the states.

The cross between this stallion and the Spanish Barbs influenced the early prototypes of the Quarter Horse breed.

By the late 1700’s/early 1800’s, American settlers were expanding west. They were breaking ground, working cattle, and needed a hearty breed of horse that could keep up with the rough and tumble frontier life.

The early Quarter Horses fit the bill almost perfectly.

While there were several influential Quarter Horse stallions at the time, the influence of the Mustang is also worth mentioning. Mustangs were descendants of the horses brought over by Spanish explorers, and their genetic contribution was, in part, pure grit.

Slowly but surely, the breed developed into what is known and recognized today as the American Quarter Horse. This breed is known for its athleticism, dependability, and “cow sense,” and excels in a broad range of events.

The Quarter Horse has been carefully honed to get a variety of jobs done throughout history. From plowing to racing to working cattle, the American Quarter Horse has risen to the occasion time after time and is the world’s most popular horse breed today.

Quarter Horse

The History of the Thoroughbred

The story of the Thoroughbred also starts in England. It began with three foundation stallions initially imported to England from the Middle East in the 17th century.

These stallions include the Godolphin Arabian (remember him?), the Byerly Turk, and the Darley Arabian.

By the 18th century, English horse racing had risen substantially in popularity. The early Thoroughbred breeders were interested in combining only the very best stallions and mares to produce superior track horses.

Aside from its speed and athleticism on the track, the Thoroughbred is known for its impeccable breeding records which date back to the first General Stud Book published in 1791. Pedigrees of each of the 387 mares included in the first book could be traced directly back to at least one of the three foundation stallions.

The studbook concept made its way overseas. The first American version was published in 1873. Starting in the 1970s, inclusion in the registry required blood-typing, later followed by DNA-typing, to verify lineage.


Records both in America and overseas continue to this day, documenting pedigrees and race results with the overarching goal of tracking gradual improvements to the breed over time.

Thoroughbred racing in America dates back to the early 1700s. Today, it is a multi-million dollar industry. Names like Man o’ War, Citation, and Secretariat continue to fascinate and intrigue.

Stories of dramatic finishes and wins against all odds dominate the sport and keep people coming back for more.

If you peel all of that away, you’ll find a breed known not only for its athleticism, but also for its heart.

Between the grit of the Quarter Horse and the heart of the Thoroughbred, is it any wonder that breeders eventually began crossing the two?

Appendix Characteristics

Crossing two different horse breeds results in a degree of body type and personality variability. Depending upon the exact influence of either breed, some Appendix Quarter Horses tend to be taller and leaner (thanks to their Thoroughbred influence) or more muscular (a throwback to their Quarter Horse lineage).

This cross also has a reputation for intelligence and a reasonably even-keeled personality.

Individual personalities often have more to do with characteristics from a particular bloodline than the breed as a whole.

Despite trends and similarities, anyone who has known and loved a horse in their lifetime will tell you that every horse has their own unique personality!

Appendix QH headshot

“Absolute Martini” an Appendix Quarter Horse out of Only Blue Sky

Registering an Appendix

Owners have two registry options when registering an Appendix Quarter Horse.


Foals resulting from the first generation cross between a Thoroughbred and Quarter Horse are eligible for Appendix registration. The sire and dam must also be registered with their respective associations.

Registration of a foal resulting from a cross between an Appendix and registered Quarter Horse is also permitted. Crossing an Appendix with an Appendix results in a foal that cannot be registered with AQHA.

There are additional rules regarding registration outlined in their rule book, such as a limitation on the total surface area of white markings. Pintos or horses with excessive white are not considered eligible for registration.

An Appendix Quarter Horse is eligible for full registration with the AQHA if the horse achieves a Register of Merit in either showing or racing.


Registration through the AAHA is more lenient. For example, foals resulting from crossing two Appendix Quarter Horses are permitted.

This registry also recognizes foals with color, including paints and pintos.

Of course, to complicate things, it is also possible to double register a horse with both associations assuming the rules for each respective association are met.

How an Appendix registration certificate is different from a non-Appendix Quarter Horse

There is a slight difference in registration certificate when registering an Appendix through the AQHA. Purebred Quarter Horses registered through this association are assigned a registration number.

In contrast, Appendix Quarter Horses are also given a registration number, but it is preceded by an “X.”

An Appendix Quarter Horse can obtain permanent registration (a number without an “X”) by earning a Register of Merit in either showing or racing.

This difference exists only with the AQHA and not with the AAHA.

Crosses to Create an Appendix

The AQHA recognizes a first-generation cross between a Thoroughbred and a Quarter Horse as an Appendix. Both the sire and dam must be registered with their respective associations.

Crosses between a Quarter Horse and an Appendix are also recognized.

The AAHA recognizes a broader range of crosses, including first-generation crosses between a Thoroughbred and a Quarter Horse, crosses between two Appendixes, and any variation. This association has no restrictions on color.

It includes paints and pintos as long as their lineage consists of a combination of Thoroughbred and Quarter Horse breeding.

Events Appendix Horses Love



3 horses leaning over a fence

Thanks to the diversity of both breeds, Appendix horses excel in a wide range of events.

Appendix horses place well in a variety of events ranging from jumping to dressage to Western pleasure. They can also excel on the trail and in contesting events, such as barrels.

The versatility and athleticism of this breed can also translate to a successful all-around horse.

Drawbacks of Appendix Horses

Every horse is an individual. They all come with their own set of quirks, so while as a whole, Appendix quarter horses are a relatively docile and trainable breed, there is always an exception to the rule.

Thoroughbreds have been bred to race and can pass along higher energy and a degree of stubbornness to their progeny, even in combination with more laid-back Quarter Horse bloodlines.

Quarter Horses are prone to several genetic disorders such as hyperkalemic periodic paralysis (HYPP) and malignant hyperthermia, which can be debilitating or even fatal.

Appendix QH in pen

What can’t you do with an Appendix horse?

The short answer is that there isn’t much that can’t be done with an Appendix horse!

All horses are individuals and should be treated as such. If you’re considering the purchase of an Appendix (or any!) horse, it’s always worth a pre-purchase vet check and input from a trainer you trust to make sure the horse is a fit for you and your sport.

Frequently Asked Questions

Horse gazing in the distance

Image courtesy of Canva

Q: What is the difference between an Appendix Quarter Horse and a Quarter Horse?

An Appendix Quarter Horse has varying degrees of Thoroughbred bloodlines. A Quarter Horse (as recognized by the AQHA) has strictly Quarter Horse breeding. It could, although, be reasonably argued that all Quarter Horses have Thoroughbred breeding if you go back in history far enough.

By today’s standards, an Appendix is a mix of Quarter Horse and Thoroughbred breeding.

Q: What are Appendix Quarter Horses good for?

Thanks to the athleticism of Thoroughbreds and Quarter Horses, Appendix Quarter Horses do well in a wide range of events. You can find them in hunter classes, on the trail, in the pleasure ring, and even in the dressage arena.

Few breeds are quite as versatile as the Appendix Quarter Horse.

Q: What is an AQHA Appendix Certificate?

Registration of Appendix Quarter Horses is recognized by the AQHA. Horses are eligible via two separate routes. The first is a direct cross between a registered Quarter Horse and a Thoroughbred registered through the Jockey Club.

The second route is by crossing a registered Quarter Horse with an Appendix.

Horses on the Appendix registry have an “X” before their registration number, which designates their Appendix status.

Appendix Quarter Horses can become eligible for full registration with the AQHA by reaching Register of Merit status in either showing or racing.

Q: How much does an Appendix horse cost?

There is quite a bit of variability in the price for an Appendix horse. Most registered horses command a higher price point than an unregistered (or grade) horse of similar training.

You should expect to pay anywhere between $2,000 and $20,000 for a horse of this breed.

Prices may be significantly higher than $20,000 for horses with extensive training and/or proven show history in a specific area.

Training level, breeding status, discipline, age, and physical condition contribute to the wide price range for an Appendix horse.

Q: Do Appendix horses make good trail horses?

There is some variability within individual Appendix horses, but many do make reliable trail companions.

Appendix horses generally display higher-than-average endurance thanks to their Thoroughbred breeding.

And their Quarter Horse bloodlines contribute a calm, “been there, done that” type of demeanor.

Q: Are Appendix horses good for beginners?

It depends on the individual horse’s history, training, and life experience.

Some Appendix horses are fantastic beginner horses, while others are best saved for professionals.

Thoroughbreds are notoriously “hot-headed,” while Quarter Horses have a reputation for their even-keeled temperaments.

Thanks to contributions from both breeds, an Appendix horse’s temperament could go either way or be a combination of both.

Generally speaking, temperament tends to be a highly heritable trait. This means you can look to a horse’s sire and dam to preview the foal’s general demeanor.

If you’re new to horses, connect with a horse trainer in your desired riding discipline.

A professional trainer can help you make the right purchasing decision for your riding situation and ability.

Q: What is a grade horse?

In the horse world, “grade” means unregistered.

Most breed registries require both the sire and dam to be registered for the foal to be registered.

And in many cases, registries are based on purebred horses, meaning both sire and dam are the same breeds.

Certain registries recognize specific crossbreeding, such as in the case of Appendix horses.

One significant benefit of registration is the ability to track bloodlines. Certain registries also screen for genetic heritability for diseases like Hyperkalemic Periodic Paralysis (HYPP). Beyond tracking bloodlines and genetic traits, still other owners pursue registration to participate in breed-specific competition.

And formal registration tends to increase a horse’s value.

But plenty of grade horses out there excel in all disciplines, despite their lack of formal registration.

Again, it all comes down to the horse’s individual temperament, training, and personality.

Parting Thoughts

There you have it—the story of how two separate horse breeds eventually found their way together. Thanks to the enterprising spirit of horse breeders who saw the potential long ago, we are blessed with a breed that carries both grit and heart.

The Appendix is a breed that excels in a wide variety of events and whose intelligence and athleticism leave a lasting impression on those who know and love them.

P.S. Enjoy this article? Trot on over to: 


History of the Quarter Horse – AQHA

What Is a Quarter Horse? – AQHA

Thoroughbred | International Museum of the Horse (imh.org)

A Winning Combination: Appendix Quarter Horse – Horse Illustrated

Appendix horse breeders horse registry. Thoroughbred Quarter Horse cross breed known as the Appendix bred. This is a stand alone membership and bloodline pedigree full service horse registry. – American Appendix Horse Association

Breeding a Thoroughbred to a Quarter Horse: What to Know – AQHA

American Appendix Horse: Breed Profile (thesprucepets.com)

Malignant Hyperthermia (MH) | School of Veterinary Medicine (ucdavis.edu)

Love it? Share it!

About the author


Aimee B.

Aimee grew up riding and showing in western pleasure and horsemanship through 4-H. She began riding dressage 7 years ago and is currently training her 3.5-year-old Friesian/Quarter Horse.