Genetic Deep Dive: Can Eton the Mustang be a Friesian? The American Mustang's Ancestry & Composition

Elisa Wallace is a 5 star three-day event rider, YouTuber, and advocate for American Mustang adoption, off the track thoroughbreds, rider safety, and women in sport. Elisa is passionate about her work with American mustangs, aimed at demonstrating the potential of this misunderstood breed. One Mustang that Elisa rescued captured the hearts of her community from the day he came home on June 7th, 2019 - Eton!

Eton is an 8 year old Mustang gelding from Green Mountain HMA, Wyoming and just 14.1 hands tall. Elisa named Eton after one of the mystical black horses that pulled Pluto’s Chariot and was rendered “swift as an eagle”. Elisa adopted Eton in order to participate in the Mustang Tip Challenge, in which trainers have 90 days to train a mustang for an in-hand competition held in Fairburn, GA.

“I don’t know how many times I’ve been asked, or told, that Eton looks like a Friesian" Elisa said on her Youtube Video "Is my Mustang a Friesian?". Elisa decided to run an Etalon Diagnostics Ancestry & Composition Analysis and MiniPanel PLUS Diagnostic test on Eton to learn more about his genetics. Etalon's ancestry and composition analysis is an in-depth comparison of your horse's genetic make-up and how it is like, or unlike, other horses within various "breeds", disciplines, and populations around the world.

The short answer: Eton is not a Friesian! In fact, when Etalon’s full-time geneticist, Laura Patterson Rosa DVM, PhD looked closely at his results, she noticed that he is genetically very far from a Friesian. Yet, Eton's DNA provides a lot of insight into what makes up the American Mustang. Read on to learn more about how Eton's DNA differs from a Friesian. Let’s look at “breeds” that he is most closely related to, how we interpret this information, and why it matters.

First, let's take a look at a purebred Friesian's Ancestry results…

Meet Zero Gravity, or “Z”. Z is a 1997 Purebred Friesian Stallion. His Etalon Diagnostics ancestry results came back just as expected: Z is 99.9% “European Heavy Horse”. The European Heavy Horse population originated in Europe and includes breeds such as Belgians, Clydesdales, the Fell Pony, Franches Montagnes, and Percherons. Taking an even closer look at Z’s Ancestry and Composition Analysis results, Etalon provided his owner with an Ancestry breakdown to illustrate just how he compares to certain breeds from around the world. Here’s a look at Z’s results:

Z’s DNA was most closely related to a Belgian’s at 84%. Next was the Fell Pony, at 14%. Lastly, Z’s DNA was only slightly related to a Clydesdale’s at 1%.

Take note of Z’s inbreeding coefficient score of 32.59%... we’ll get to that soon and why that’s important!

Now, let’s take a look at our friend, Eton…

Eton’s DNA looks drastically different from Z’s. Eton’s ancestry results prove just how genetically diverse he is as an American Mustang, with his DNA originating from several different populations from around the world. The most prominent population being the European Heavy Horse, at 34.4% similarity. Coming in second, Eton’s DNA was 17.2% related to the “Carriage Horse” population, which includes breeds such as the French Trotter, Morgan, Saddlebred, Standardbred, and Tennessee Walking Horse. The next population Eton is related to is the Iberian, including Andalusians, Lusitanos, and Mangalargas. Next is the North Sea group, including Fjords, Icelandic horses, and Shetlands. Eton has 11.7% Thoroughbred blood, and is slightly related to the Exmoor and Near East horses.

Look at all of those breeds hard at work in Eton! Something interesting to note is that, while Eton is most closely related to the European Heavy Horse population, his related breeds are not the same as Z’s, the purebred Friesian stallion we met earlier. Again, Z was most closely related to the Belgian breed, with Fell Pony a distant second. Within the European Heavy Horse population, Eton is most closely related to the Franches Montagnes, with Belgian as a second, and Clydesdale and Fell Pony arriving third and forth.

So… what breed is Eton most closely related to, if not a Friesian?

Here’s a look at a few breed averages that look similar to Eton’s. The New Forest Pony is the closest match, and Appaloosa and Irish Draught are close. Pretty random breed combination, huh? We think so too…

“Our Ancestry panel is looking much deeper and farther back than you might realize. We are looking at DNA through the lens of thousands of generations back, trying to assemble the puzzle pieces, so his results make a lot of sense”, said Dr. Patterson Rosa. The American Mustang is so genetically diverse that it’s difficult to analyze and assign him a ‘breed’. ‘Mustang’ simply means that the horse is feral, and the American Mustang has been influenced by many different breeds over the past several generations.”

The first Mustangs descended from horses brought to the Americas by the Spanish, that escaped or were released into the wild. However, many other breeds and types of horses contributed to the modern Mustang, resulting in varying phenotypes. Most contain a greater genetic mixture of ranch stock and more recent breed releases, while a few are relatively unchanged from the original Iberian stock strongly represented in the most isolated populations.

In Eton’s case, he still has strong Iberian bloodlines, with the Iberian group coming in at 15.9% of his DNA. His most prominent population, the European Heavy horse, makes sense when compared to more recent Mustang history. In the United States, “pit ponies” had a large influence on the Mustang herd population. These horses were used underground in mines from the mid-18th until the mid-20th century. Mining horses were often low set, heavy-bodied and heavy-limbed with plenty of bone and substance. European Heavy Horses, such as Belgians, were often used in the mines. A number of these horses are presumed to have been released or escaped, which would explain the large presence of heavy horse “blood” in Eton. The Mustang population was also heavily influenced by Army Remount horses, Western ranchers, and various settlers. Their breed composition is quite genetically diverse, with Mother Nature having a lot to say over which traits survive in these horses and which traits are quickly eliminated.

“Eton’s Ancestry results also tell us a lot about what Mother Nature favors!” said Dr. Patterson Rosa. Eton’s genetic makeup gave him the best capacity to survive in the wild by himself. Taking a look once more at his Etalon Ancestry results, we notice that Eton’s inbreeding coefficient score is quite low: only 4.6%. Inbreeding coefficient is a measure derived from the actual genetic diversity within the individual. By comparison, Zero Gravity (the purebred Friesian stallion) has a very high inbreeding coefficient of 32.59%.

“In domestic animals, to create breeds, people inbreed or ‘linebreed’. Humans want certain traits to be prominent in a population. In doing so, however, we increase the chances that lethal or disease alleles become more present in that population as well. Highly inbred individuals do not tend to survive in harsh conditions. Mother Nature selected Eton as an efficient horse, capable of surviving and adapting to whatever she threw his way while living as a feral horse in Wyoming. Increased levels of heterozygosity are correlated to a better environmental and immune adaptability. Eton is actually so adaptable, that he was capable of being removed from his natural environment in Wyoming, handled by humans for the first time, moved to Florida where the conditions are drastically different, and adapting to all of the new things Elisa taught him. From being handled to ridden to competing in his first horse show, Eton is adaptable.” said Dr. Patterson Rosa.

So, why does all of this information matter?

As a horse owner, understanding your horse’s genetic makeup can help make their lives easier by understanding suitability. Horses are genetically suitable for some careers, disciplines, or even people, over others!

By taking a look at these Ancestry averages from certain disciplines, it’s simple to interpret the findings. For example, the 3-Day eventing horse has significantly more Thoroughbred blood than the Reining horse does. This makes sense because of the difficult nature of cross country and show jumping; requiring horses to be able to run for long distances and display incredible levels of athleticism. Reining horses have more Carriage horse blood, giving them the powerful shoulders and hindquarters to get low to the ground and spring back up quickly.

Comparing your horse’s Ancestry results to different breeds and disciplines from around the world may help you as a horse owner when it comes to decision making, and increase the number of tools in your and your horse’s toolbox. It’s all in their DNA - who these horses are, how they behave, their suitability for one discipline over another, speed, gait - the list goes on.