World's first gene-edited horses are shaking up the genteel sport of polo

 They look like ordinary foals, docile with honey brown coats and white facial patches, content to spend their days munching alfalfa in a cordoned-off pasture in rural Buenos Aires province.

But these five 10-month-olds are the world's first genetically edited horses: cloned copies of a prize-winning horse named Polo Pureza, or Polo Purity, with a single DNA sequence inserted using CRISPR technology with the aim of producing explosive speed.

Kheiron Biotech, the Argentine company that created the horses, says gene-editing has the potential to revolutionize horse breeding.

Daniel Sammartino, co-founder of Kheiron Biotech, which produced the world's first genetically edited horses.

While cloning creates a genetically identical copy, CRISPR functions as a sort of genetic scissors to cut and customize DNA. The company, which specializes in equine cloning, used CRISPR to reduce the expression of the myostatin gene, which limits muscle growth. The idea was to increase the muscle fibers that allow for powerful movements and so transform the horses into sprinters.

But polo isn't letting them in so fast.

While Argentina, regarded as the global capital of polo, has long welcomed reproductive technologies - including cloning - to breed elite horses, the sport's national body and breeding association are putting up hurdles to prevent GE horses from joining the game.

A man hits the ball as he plays during a polo training session, in Canuelas, Buenos Aires, Argentina.

The Argentine Polo Association has banned GE horses from competition.

"I wouldn't like them to play polo," said Benjamin Araya, the association's president. "This takes away the charm, this takes away the magic of breeding. I like to choose a mare, choose a stallion, cross them, and hope that it will turn out very well."

And the Argentine Association of Polo Horse Breeders told Reuters it will monitor the horses for four or five years before making a decision on whether to register them as Argentine polo ponies.

An employee of Kheiron Biotech sorts oocytes from horses, at their laboratory in Pilar, Buenos Aires.

Kheiron said it was confident the polo community would eventually come around. "The truth is that I'm not so worried about it," Gabriel Vichera, the company's scientific director, told Reuters. "Educating, I think that's what we have to keep doing." It's unclear how the sport's national body would enforce a ban. Argentine regulations do not distinguish between cloned, GE and conventionally bred horses and neither does the polo association.

Some breeders said that while they appreciate how clones can help preserve the bloodlines, gene-editing goes too far and could threaten their business.

THE $800,000 HORSE "This ruins breeder," said Marcos Heguy, a breeder and former professional polo player. "It's like painting a picture with artificial intelligence. The artist is finished." Eduardo Ramos, who began breeding in the 70s, said that breeders had also been skeptical at first of other advances in biotech, such as embryo transplants and cloning.

A horse carer walks near the world's first genetically edited horses, designed by Kheiron Biotech to achieve exceptional speed, in an enclosure.

"Science and technology will keep advancing," he said. "Those who say this shouldn't be done won't be able to stop it." Polo, which originated in Central Asia, was brought to Argentina by British immigrants, who founded the first polo club in Buenos Aires in 1882. It's somewhat like hockey on horseback, where two teams of four people each sweep long mallets to drive a ball through goal posts.

It's expensive - players ride as many as a dozen horses per game - and in Argentina, wealthy land-owning families have traditionally dominated the sport. The country exported about 2,400 polo horses last year, according to government data, and the Argentine polo breed dominates prestigious competitions like the Queen's Cup in England and the Argentine Open. The sport has long used surrogates to carry embryos of polo-playing horses. And unlike horse racing, polo allows cloned animals.

The world's first cloned horse was born in 2003. Adolfo Cambiaso, widely considered the world's top player, helped popularize polo clones. When a clone of Cambiaso's prized Cuartetera sold at an auction in 2010 for $800,000, the amount caught the attention of Vichera, then a biotech doctoral student. Vichera went on to co-found Kheiron the next year with backing from businessman Daniel Sammartino. Its first cloned horse was born in 2013. Cloned horses weren't an easy sell at first. To get going, Sammartino said he provided free cloning services to top breeders, who allowed him to keep some of the newborn clones in exchange. By this year, the company says it will produce 400 clones, more than half of all the cloned horses born in Argentina in 2025, according to the breeders' association's estimates.

Oocytes from horses appear under a microscope at Kheiron Biotech's laboratory.

The cloned foals sell for an average of $40,000, Sammartino said. In 2017, the Kheiron lab used CRISPR genetic editing to produce nine GE horse embryos for research purposes.

That upset some prominent figures in Argentina's polo world who visited the government's biotech regulator, concerned about the possibility of gene-edited horses entering the sport, said Martin Lema, who headed the agency at the time.

For the next few years, Kheiron said the lab focused on other animals, producing gene-edited cows and pig embryos designed for human transplants. Then late last year in the gaucho town of San Antonio de Areco - where farm hands still wear berets in traditional cowboy culture - Kheiron's birthing clinic produced the five GE foals.

PLANS PAUSED

Argentina's biotech regulator verified the DNA edit, according to a government document reviewed by Reuters. The department of agriculture, which oversees the agency, declined to comment.

A cloned newborn horse stands next to its surrogate mother in a pen at a horse birthing hospital.

About 50 breeders signed on to a letter to the breeders' association that said the gene-edited horses were "crossing a limit" and asked not to register the horses without "a profound reflection on where we want to go." Although Santiago Ballester, the president of the association, said he personally has "no problem" with genetically edited horses, he acknowledged the concerns of fellow breeders about how gene-editing would affect their business, and whether countries that import Argentine polo horses would accept gene-edited ones.

The association decided to tread cautiously.

"Let's be careful, responsible," Ballester said. "We have to see what impact these horses will have, if they are really superior animals. If they are normal, who is going to pay money for this?"

Ted Kalbfleisch, a geneticist at the University of Kentucky's Gluck Equine Research Center, said that Kheiron's insertion of a natural DNA sequence simply sped up traditional modifications, which can take several generations.

"Where things get sketchy is when you're trying to maybe make edits you're guessing about," he said. But with myostatin, scientists edited "a gene that we know is present in healthy horses. When they take that and edit it into a clone, provided they do it faithfully… it ought to work."

Surrogate pregnant horses graze in a corral. Photos: Reuters

Although Kalbfleisch said that gene-edited horses may have an advantage in polo tournaments, it's not necessarily an unfair one.

"This technology, the cloning and the gene editing, are pretty well democratized right now," he said. "If you can write a check you can get it done."

The horses still have a ways to go before they hit the polo field. At age two, they'll start easing into a saddle. A year or two later, they'll begin learning polo.

But Sammartino admitted that plans to commercialize their gene-editing service are on hold until the polo authorities are on board. The pause has frustrated Sammartino, who said he had been contacted by a dozen potentially interested clients in Argentina, though he declined to put Reuters in contact with them, citing privacy reasons.

Even so, Sammartino acknowledged that an element of uncertainty remains.

"Will it be a better horse? I don't know. Time will tell."

Reuters