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horses—an endangered species whose entire population today descends from a very limited number of wild ancestors.
The Przewalski’s horse (Equus przewalskii), once extinct in the wild, was saved through being bred in captivity and later reintroduced into its native habitats. This recovery program has been highly successful - with approximately 3,000 individuals alive today. However, it is important to recognise that all these horses trace back to just 12 wild-caught animals, captured between 1898 and 1947. As a result, the current global population is genetically narrow, with only five founder lineages represented in today's horses.
To address this genetic bottleneck, scientists are exploring advanced reproductive technologies, including cloning from cryopreserved cells. This approach could either restore lost genetic variation or amplify the presence of underrepresented lineages in the population. Such efforts rely on biological materials preserved in biobanks specifically for conservation purposes.
Since the 1970s, the San Diego Zoo Wildlife Alliance’s Frozen Zoo® - a major component of their Biodiversity Bank - has stored cells and tissues from 575 Przewalski’s horses spanning many generations. Among these samples was one from a stallion known as Studbook Number 615, or "Kuporovitch," who lived from 1975 to 1998. Despite his valuable genetics, Kuporovitch was underrepresented in the breeding program, making him an ideal candidate for cloning.
In a study published in the journal Animals, Ben Novak and colleagues reported the successful birth of two healthy clones of Kuporovitch. These clones were created using cross-species somatic cell nuclear transfer - a method in which the nucleus of a preserved Przewalski’s horse cell is inserted into an enucleated domestic horse ovum (egg), which is then implanted into a domestic horse surrogate mother. The first clone was born in 2020, followed by a second in 2023.
Both clones were genetically verified using standard pedigree genotyping, and one clone’s identity was further confirmed through whole-genome sequencing.
The research team point out that this is the first time multiple clones of an endangered species have survived the perinatal period, marking a significant achievement in conservation science.
They add that, although only two clones were produced, both attempts at cloning were successful, demonstrating the reproducibility and reliability of cloning for genetic rescue purposes for the endangered Przewalski’s horse.
This breakthrough makes the Przewalski’s horse only the fifth endangered species to be successfully cloned, and one of the first where cloning has been used as an active tool for conservation management. It opens the door to more strategic use of biobanked genetic material in future recovery efforts - not just to prevent extinction, but to enrich and diversify the genetic makeup of rebounding populations.
For more details , see:
Novak, Ben J., Oliver A. Ryder, Marlys L. Houck, Kelcey Walker, Lexie Russell, Blake Russell, Shawn Walker, Sanaz Sadeghieh Arenivas, Lauren Aston, Gregg Veneklasen, and et al. 2025.
Endangered Przewalski’s Horse, Equus przewalskii, Cloned from Historically Cryopreserved Cells
Animals (2025) 15, no. 5: 613.
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