For generations, the world’s top horse breeders have carefully mixed bloodlines for temperament, strength, conformation and athleticism. Each new foal bore the promise of outperforming a carefully chosen set of parents. It isn’t quite natural selection, but it isn’t far off.

Now the equestrian world might be hitting a plateau: exact genetic replicas of successful horses and ponies. In other words, clones.

Some worry about losing the ability to breed ever-better horses and happy accidents that push the sport forward, if too many people decide to opt for a clone.

Polo player Adolfo Cambiaso, regarded by many in the sport as the greatest of all time, essentially created the sporthorse cloning industry when he made a slew of genetic copies of his best ponies, starting in the early 2000s—and began winning tournaments on them.

In 2010, a clone of his champion mare Cuartetera sold at auction for $800,000, an eye-popping sum for a polo pony at the time. Then again, Cuartetera was known as the Messi of polo for her speed, agility and keen mind.

Now cloning is becoming more popular in other disciplines. At the end of 2024, the dressage portion of the eventing world championship for 7-year-old horses had concluded, and Chilli Morning IV was locked in a tie for second place with a horse that had remarkably similar strengths and weaknesses. Its name: Chilli Morning II.

Coincidence? Not at all. They were both clones of the late champion eventer, Chilli Morning.

Olympic gold medalist Julia Krajewski, who piloted Chilli Morning II and once competed against the original Chilli Morning, said the clones are eerily similar, and seem to share not just physical characteristics and capabilities, but also quirks.

“They’re all not big fans of sunken roads,” Krajewski said, referring to a combination of jumps on cross-country courses that test a horse’s ability to jump down, rock back and jump up again.

“In the end, it is a horse,” Krajewski said. “He doesn’t know he is a clone.”

Worldwide, the number of equine clones born a year pales in comparison to traditionally-bred horses, but those clones—and their offspring—are starting to emerge in the top echelons of different equestrian disciplines.

Cloning is a controversial practice, but particularly so in horse sports. It is banned in thoroughbred racing and competitors in other disciplines are divided, with some saying it creates unrealistic expectations and stifles advances in breeding.

“If every horse you have is your best horse, the strategy aspect of the game is gone,” said Javi López Frías, a sports ethicist and assistant professor in the department of kinesiology and health science at Utah State University. “It makes something difficult easier.”

Despite riding and competing on a clone, Krajewski said she wouldn’t consider cloning her Olympic gold-medal-winning mare, Amande de B’Neville. She worries it would set an impossibly high performance standard for the clone.

“I don’t think I’d want to put that pressure on me or the horse,” Krajewski said.

The Fédération Equestre Internationale, the governing body for Olympic horse sports, banned clones from competition in 2007. But it reversed that decision in 2012 after determining they didn’t provide competitors with an unfair advantage, due to the myriad environmental factors that go into producing a champion, like parentage, training, the rider, the type of food it eats and even the shoes it wears.

Still, the debate about whether it is the right way forward for horse sports is getting louder, as cloning progresses to gene editing.

Buenos Aires-based Kheiron Biotech, an equine cloning company, produced around 400 cloned horses during the season that ended in February, mostly of various polo ponies.

In 2024, Kheiron also produced the world’s first genetically-edited horses using Crispr technology. Those horses, clones of the Polo Hall of Fame mare Polo Pureza, have an edit in a gene that regulates muscle development.

“The expectation is that…the mare will acquire sprinter-like characteristics that she did not previously have, while maintaining her other exceptional traits,” said Gabriel Vichera, co-founder and chief scientific officer of Kheiron.

A clone from Kheiron typically costs around $40,000, although bulk discounts are available.

Still, cloned horses can reproduce normally, so bloodlines that would have been lost can be reintroduced and improved upon. That means the clones are probably not the end of the evolution of the perfect horse, and in some cases could speed up the process if their owners can look beyond the short-term gain from creating exact replicas.

“Some people are always a bit wary of the clones,” said Laura Chapot, a top-level U.S. show jumper whose father, six-time Olympian Frank Chapot, bred the legendary show jumper Gem Twist that won individual and team silver medals at the Seoul Olympics in 1988.

Gem was gelded, or castrated, as a young horse, a common practice for competition horses, because it generally makes them calmer, safer and more manageable. But given the horse’s storied career, Chapot’s late father wanted to continue his genetic line. The first clone of Gem Twist, Gemini, was born in 2008.

The horse has been used as a breeding stallion, with what its admirers say are predictably strong results.

“He very much produces a lot of the characteristics we’re looking for,” Chapot said. “Sometimes you feel like [traditional breeding is] a bit of a crapshoot.”

Write to Alexandra Wexler at alexandra.wexler@wsj.com