The first ever successful reverse vasectomy on an endangered species is performed at the National Zoo.

The Prezewalski horse came to the Smithsonian National Zoo in 2006. He was vasectomized in 1999 at a previous institution and now has had a successful reverse vasectomy.

The Prezewalski horses are a horse species native to China and Mongolia that was declared extinct in the wild in 1970. There are approximately 1,500 of these animals maintained at zoos throughout the world and in several populations in Asia.

"The major challenge we faced was that this procedure had never been performed on an equid, let alone a critically endangered species," said Dr. Budhan Pukazhenthi, a reproductive scientist at the National Zoo's Conservation and Research Center in Front Royal, Va.

The team sought out Dr. Sherman Silber, a St. Louis-based urologist who pioneered microsurgery for reverse vasectomies in humans and had been successful in vasectomizing and then subsequently reversing vasectomies in South American bush dogs at the St. Louis Zoo.

"Although our team is very experienced in horse anesthesia and surgery, by using the specialized professional skills of Dr. Silber, we greatly increased the likelihood of success," said Dr. Luis Padilla, associate veterinarian at the Conservation and Research Center.

"I've always dreamed of using my expertise to contribute in some way to wildlife survival," said Dr. Silber. "It was exciting to pioneer a new procedure for which humans were the 'test animal.'"

National Zoo scientists hope to pair Minnesota with a suitable female in July.

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