Veterinarians revealed Monday that they successfully performed the procedure on the horse to allow it to reproduce naturally. The surgery was performed in October 2007 on a Przewalski horse named Minnesota. The horses are native to China and Mongolia.

Luis Padilla, the zoo veterinarian who performed the surgery, says the procedure was a first for this species and likely for any endangered species. The team worked with St. Louis urologist Dr. Sherman Silber, who pioneered the technique in humans.

A similar surgery was successfully performed at the Saint Louis Zoo in 2003 on South American bush dogs, which are classified as vulnerable but not endangered.

The "temporary vasectomy" could have a significant impact on how animals are managed in captivity by giving zookeepers a way to control the animal's offspring without having to neuter them.

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