Scientists Cloned an Endangered Wild Horse Using the Decades-Old Frozen Cells of a Stallion

The cloned foal will hopefully provide an ‘infusion of genetic diversity’ as conservationists work to restore the Przewalski’s horse’s population

In a grassy field, a Przewalski’s horse foal stands in between two adults in a grassy field with trees in the background. The horses have a stocky build, a reddish-tan coat and dark, mohawk-like manes.
Conservationists report that the Przewalski’s horse is extinct in the wild, and only an estimated 2,000 remain in zoos and reserves. Tanya Durrant / Flickr under CC BY-ND 2.0

Two months ago, a baby horse named Kurt was born. He looks and plays just like a regular foal, but Kurt is special: He’s a clone. And he’s the first-ever clone of his species, the critically endangered Przewalski’s horse, and a shining hope for conservationists, reports the Associated Press.

Przewalski’s horses are the last living truly "wild" horses. (The stallions and mares that roam the American West descended from domesticated horses, so techincally they are feral, not wild.) These stocky, scruffy creatures once existed throughout Europe and Asia. Extreme weather, encroaching human settlements, and livestock infringing on their habitat pushed the horses as far east as the steppes of the Gobi Desert in China and Mongolia. By the 1960s, they had nearly disappeared. Conservationists report that the species is extinct in the wild, and only an estimated 2,000 individuals remain in zoos and reserves, including the Smithsonian Conservation Biology Institute in Front Royal, Virginia.

Every Przewalski’s horse descends from 12 wild ancestors, so they’re in dire need of increased genetic diversity, reports Jonathan Wosen for the San Diego Union-Tribune. Kurt’s dad offered a glimmer of hope—parts of his DNA were largely missing from other Przewalski’s horses since his ancestors likely hadn’t reproduced as much. This discovery offered much-needed hope to help restore the species’ genetic diversity—if his DNA isn’t passed down, it could be lost forever, scientists say.

In hopes of using the stallion’s DNA to breed more Przewalski’s horses, researchers at the San Diego Zoo Global froze a sample of his skin cells in their Frozen Zoo, a menagerie of 10,000 cell lines from an estimated 1,100 species and subspecies, in 1980.

“A central tenet of the Frozen Zoo… was that it would be used for purposes not possible at the time,” Oliver Ryder, director of genetics at the San Diego Zoo Global, said in a statement released last month. “Now, the living cells in the Frozen Zoo are contributing to reversing losses of genetic diversity and contributing to population sustainability.”

After 40 years of being frozen in time, scientists thawed the stallion’s cells and fused one with an egg from a female domestic horse, who would later be Kurt’s surrogate mother. They removed the egg’s nucleus—and all of the DNA stored inside—so that the embryo would be a clone of its father. It’s the same method that created Dolly the sheep, the first mammal ever cloned, in 1996.

In August, Kurt was born at a veterinary facility in Texas. His successful cloning provides hope for conservationists that one day they can restore the population of Przewalski’s horses in their native range. He’ll live with his mother for another year before transferring to San Diego, where he’ll join the zoo’s breeding herd of 14 other Przewalski’s horses. When Kurt reaches breeding age, he’ll “provide a valuable infusion of genetic diversity.”

If all goes well, conservationists hope that Kurt will sire a healthy line of offspring that could one day be returned to the wild.

Kurt's birth is a milestone in Przewalski’s horse conservation, the San Diego Zoo Global says, but this initiative to save the Przewalski’s horse will take generations, Megan Owen, the zoo’s director of wildlife conservation science tells the San Diego Union-Tribune. But they’re crucial steps, nonetheless.

“This colt is expected to be one of the most genetically important individuals of his species,” Bob Wiese, chief life sciences officer at San Diego Zoo Global, said in last month’s statement. “We are hopeful that he will bring back genetic variation important for the future of the Przewalski’s horse population.”

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