Confident and curious, the 3-year-old dun-colored Kurt leads pasturemate Holly across the sparsely covered, hilly terrain, heading towards a pickup truck. 

Whoosh. The truck driver snaps shut the window, cutting off contact with the approaching animals, the world’s only truly wild horses, Equus ferrus przewalskii. Kurt is exceptional because he is a clone of this endangered species; the horses were once extinct in the wild and with only 12 individuals in zoos worldwide. Kurt was birthed by a surrogate dam in 2020, as the product of ancient and precious cells not found in other remnants of the species. 

Though it seems natural to reach out and pet him like you might a miniature draft horse, Kurt is a wild animal intended to stay wild and, as a future breeding stallion, destined to contribute to the viability of this rare species by building a more diverse genetic base that will enable the Przewalski’s horses to respond positively to poor diet, parasites and other stressors and triggers in the wild—and to be a better version of themselves, essentially. 

Unlike mustangs or the horses of Chincoteague Island or the Brumbies of Australia that harken back to domestic horses left in the wild a few centuries earlier, the Przewalski’s horse (pronounced “shuh-VAL-skees”) diverged from a common ancestor with the modern horse 500,000 years ago. The Przewalski’s horse has 66 chromosomes, and the modern domestic horse has 64, making them different species. 

Russia, Mongolia And San Diego 

The first documentation of these wild horses was found in rock engravings and paintings in underground caves across Spain and France dating back more than 20,000 years. Tibetan monk Bodowa was the first to mention them in writing around 900 AD, and Genghis Khan reportedly spotted the horses during his Mongolian conquests. 

On the steppes of Central Asia in the late 19th century, Russian colonel, explorer and naturalist Nikolai Mikhailovich Przhevalsky came upon the skull and hide from an animal that looked like Kurt: a stocky fellow around 600 pounds, 12 to 14 hands, a coat in colors varying from beige to reddish brown with a light yellow underbelly, and dark lower legs with zebra-like stripes behind the knee. A dark dorsal stripe runs along the back to the tail. The large head ends with a white muzzle, sometimes called a flour nose. The neck is short and thick; the legs are stocky. Like the zebra, there is no forelock. The mane is short and stands straight up. 

Mongolian natives called them Takhi or “spirit.” 

Around 1900, a large number of Przewalski’s horse foals were captured and shipped to Europe. The 53 that survived the rough trip were dispersed to zoos and private parks. 

Meanwhile, back in the Russian and Mongolian steppes, the horse was hunted and suffered from habitat incursion by grazing domestic livestock; the last one was found on the Mongolian steppes of the Gobi Desert in 1969. The Przewalski’s horse was pronounced extinct in the wild. 

Today approximately 1,900 are living in the world, including some 350 Takhi in Mongolia’s Hustai National Park Protected Wildlife Preserve after 16 were introduced in 1992. While it was fortunate to have the zoo-bred representatives, such a small population makes inbreeding an issue. 

More fortuitous, however, was the capture and preservation of the cells of a stallion known as SB615, or better known to his zookeepers as “Kuporovic.” 

Born in the United Kingdom in 1975, Kuporovic came to the U.S. in 1978 and lived until 1997. In a stroke of genius, Kurt’s namesake geneticist Dr. Kurt Benirschke founded the San Diego Zoo Wildlife Alliance Frozen Zoo, where he cryopreserved cell lines of endangered species, including those of SB615. The lab safely stored them for future genetic diversity even though, at the time, cloning and the necessary reproductive technologies did not yet exist. 

Here’s the beauty of Kurt. The cell lines of Kuporovic offered more genetic variation than any living Przewalski’s horse. SB615 was a descendant of the unique ancestry of two wild founders of the species, SB11 and SB12. In fact, SB615 carried significantly more unique alleles (or variants of genes) from those wild founders than other living Przewalski’s horses. 

Because of these cryopreserved cells, SB615 lives today as young Kurt. 

Nearly 50 years after Benirschke put his plan together, a partnership was formed to conserve endangered species through genetic rescue. In February 2017, nonprofit organization Revive & Restore co-founders Stewart Brand and Ryan Phelan and lead scientist Ben Novak approached ViaGen Pets & Equine to discuss the potential for cloning endangered species. That company’s advancements in the commercial cloning of domestic species made it clear that the technology was no longer a theoretical or academic endeavor. 

When Revive & Restore reached out to Dr. Oliver Ryder, director of wildlife conservation at the San Diego Zoo Wildlife Alliance and the Frozen Zoo, horse lover and dressage rider Phelan was thrilled that the Przewalski’s horse was a worthy candidate for cloning. 

The result was Kurt, born on Aug. 20, 2020, in Texas to a Quarter Horse mare. 

Kurt And Holly 

As a clone, on a DNA level, Kurt is the same horse as Kuporovic. He is those cells. He doesn’t look like a domestic horse, and how he looks is not why he will help to preserve the wild horse. He is essential for the genetics inside, not for phenotypic traits. The plan is that in a couple of years, when he is a fully mature stallion at 4 or 5 and ready to breed, he will join the San Diego Zoo Safari Park’s herd of adult females, with Holly, of course, and become the herd stallion. 

“Our role at the Safari Park is to create genetically diverse horses to supply reintroduction efforts into the wild. The line in Kurt is not represented in the wild population. The idea is to create foals that could be part of that population,” explains Gavin Livingstone, curator of mammals at the San Diego Zoo Safari Park. 

Holly is not as genetically distinct as Kurt, but she has much to contribute. Born in the El Paso Zoo, she was paired up with Kurt to teach him Przewalski’s horse and wild horse behavior, things he would not learn from his surrogate mother or the domestic foals from his early life. 

As of now, Holly has contributed part of her tail. Kurt has chewed it off, a wild and stallion behavior Livingstone is happy to see. Similarly, Kurt’s people were delighted when as a foal Kurt aggressively protected his surrogate mother, again a wild horse and stallion behavior. 

“They can be more aggressive with other animals. They will be more amped up. You see them kicking, being rough with each other, mane biting, and tail pulling. That’s how they speak to each other,” he says. “Nature intended them to be rough and tumble horses. They’re not tall. They have big thick legs, all muscle. They have shorter muscular necks. They are made to run and buck and kick and fight. 

“Kurt and Holly spent 18 months together in an off-habitat part of the park, getting to know each other, growing up a little, and learning wild horse behavior,” adds Livingstone. “Now they are in public view on 10 acres, which gives them space for body and hoof conditioning.” 

Livingstone describes them as “watchdogs of the habitat.” 

“They notice any change in the valley, like a giraffe moving closer in a different field,” he says. “At dusk, they travel up the hill for a better vantage point. They whinny back and forth to the Przewalski’s horse herd in the field above them. They are very spatially aware. They are never haltered. They are never groomed. They are never petted. These human behaviors make them too friendly and tractable.” 

Recall with positive reinforcement is the basis of their behavior training. For example, their feet are trimmed quarterly or twice a year. Kurt will put his hoof on a block to be trimmed under stimulus control without being haltered or immobilized. 

“The training allows husbandry work but respects that it is a wild horse, not a domestic animal. They’re not pets,” says Livingstone. “We don’t want to blur that line. We want them spirited, not tractable.” 

The Przewalski’s horse has good hoof quality by nature, and the Safari Park’s Central Asia habit promotes good hoof wear. “Since it’s a wild horse and the genetics is pretty robust, we don’t see a lot of negative genetic traits in the hoof quality as we might see in domestic horses,” he says. 

A nutritionist regularly body condition-scores them to prevent founder. Their diet is based on low-calorie Bermuda hay and a wild herbivore pellet. 

“In the steppe, you have a very short grass season,” says Livingstone. “At other times of the year, they get low-quality grass by forging through the snow. We monitor the seasonality of their food as well, making sure that during the time of the year that they would experience low-calorie intake, we’re not inadvertently amping up their intake.” 

The climate and terrain in San Diego are not the same as in the Gobi Desert, where the last wild Przewalski’s horse was seen in 1969, but it’s not as far off as you might expect. 

Instead, they are trained in a way that maintains their natural behaviors while allowing their keepers to give them care. In response to a bell, they run into the boma, or barn, made of shoots and alleys. As they run across an in-ground scale, they get weighed, which is especially important with Przewalski’s horses as their tendency to put on the extra pounds is a major concern. 

The Gobi has springs, steppes, forests and high mountains. Mongolia, the size of Alaska, has a large expanse of unaltered grassland. Temperatures can range from 104 degrees Fahrenheit in the summer to 50 degrees below zero in the winter. 

The successful cloning of a Przewalski’s horse is not just about Kurt. The bigger story is how science has applied cloning and embryo transfer technology to conservation science. 

The magic began in the lab, where an embryo of the Przewalski’s horse is created by hollowing out a domestic horse embryo, taking out the domestic horse genes, making it an empty vessel, and placing in it the SB615 cells. The embryo was then implanted in Kurt’s surrogate dam at ViaGen Pets & Equine in Cedar Park, Texas, where Kurt was born. 

“Mixing cloning and embryo transfer technologies, you have the base embryo to go into the recipient female. Otherwise, it wouldn’t stay in there or wouldn’t be a pure wild horse,” says Livingstone. “Today, we freeze as much as we can because we don’t know what the future holds for distinct genetic lines, or what will be endangered 30 years from now. So, it’s important to preserve as much genetic material as we can as a backstop to extinction.” 

When Kurt and Holly were turned out together, all the wildness broke loose—kicking and bucking and biting—Kurt no more and no less than Holly. At one point, the two stocky missiles stopped, stared at each other, and each did to the other the behavior known as “baby mouth,” whereby a young horse chews, signaling to a more dominant horse, “I’m a baby; don’t hurt me.” 

Who knows where and how Kurt learned this behavior? Since then, however, Kurt has taken command as his genes predicted. Witness Holly’s tail. As a prototype for the future genetic rescue of endangered and extinct species, Kurt/ SB615 is shining as the bright future of wildlife restoration. 

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This article originally ran in the Spring 2023 issue of The Chronicle of the Horse Untacked.

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