DVMs partner with human microsurgeon to reverse vasectomy

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Aug 01, 2008


Careful cutting: After two surgeries to reverse his vasectomy, Minnesota can help keep his species’ gene pool diverse so it can be reintroduced into the wild.
Washington — A team of reproductive experts performed what is believed to be the first reverse vasectomy on an equid at the Smithsonian National Zoo.

Minnesota, a Przewalski's horse, was vasectomized in 1999 before being brought to the National Zoo in 2006. At the time, he wasn't an important part of the gene pool for his species, which was declared extinct in the wild in 1970. But after a review of the 1,500 horses kept at zoos around the world, it was determined that Minnesota's genetic contribution is highly valuable to the continuation of the species.


Desirable DNA: Minnesota, the Przewalski's horse shown here, was found to be extremely valuable genetically to his species after he was vasectomized.
The only problem was that no one had ever performed a reverse vasectomy on an equid, primarily because of the dangers involved in having them on their backs for the time it would take to complete the surgery.

A collaborative effort begun in March 2007 changed that.

Dr. Budhan Pukazhenthi, a reproductive scientist who worked as a veterinarian in his native India, and Dr. Luis Padilla, an associate veterinarian, both of the National Zoo's Conservation and Research Center in Front Royal, Va., took on the case and began researching how they could reverse Minnesota's seemingly permanent sterile condition.

Almost immediately, both reached out to a human fertility specialist they knew could help — Dr. Sherman Silber, director of the Infertility Center of St. Louis.

"When this problem was presented to me with this particular stallion, the first name that popped into my head was Dr. Silber," says Pukazhenthi, adding that Silber has performed thousands of reverse vasectomies on humans and also had worked with St. Louis zoos, reversing the vasectomies of South American bush dogs and primates.

Silber signed onto the project without hesitation, donating his and his staff's expertise.

"Anytime you can apply clinical work and clinical science beyond that realm to the animal world, it's really thrilling, Silber says. "For horse lovers everywhere, I think it's kind of thrilling to bring back from almost extinction the progenitor of their favorite animal."

In their first attempt in March 2007, Padilla says he and Silber tried approaching the surgery while Minnesota was on his side. But heavy scar tissue from the original vasectomy and his positioning made things difficult.

"There was just no way we could get adequate access," Silber says.

A test a few months later proved the surgery was unsuccessful. So the doctors began to brainstorm and decided they could risk a dorsal surgery, with Minnesota on his back, but only for a limited time.

For human patients, a reverse vasectomy can take up to two hours, Silber says. But in the dorsal position, he only had one hour to complete his challenge.

"We had to know exactly what we were doing because we could only have him on his back for an hour," Silber says. "We didn't really have thinking time in this situation; we just had to move."

In October 2007, with the help of gravity in the dorsal position, Silber says he had better access. The biggest problem he faced in moving from humans to animals, he says, was the tougher scrotal skin in animals. Entering through the groin instead of the scrotum, a technique he discovered working with the dogs and primates, helped, Silber says.

Six months later, the doctors discovered their work paid off when a semen sample from Minnesota proved he could sire more of his species.

"Animals are so precious, we don't try anything on animals we haven't tested on humans," Silber jokes before becoming serious. "I've always dreamed of using my expertise to contribute in some way to wildlife survival. It also was exciting to pioneer a new procedure for which humans were the test animal."

Not every species-management program will want to attempt the procedure, Padilla says, but adds it's another option. Other options for species management that are less permanent, like gender separation and hormone treatments, can present other problems, Pukazhenthi says. Vasectomies are the most effective way to control zoo populations, which is critical with exotic and large animals because the institutions that can care for them only have so much space and resources.

The doctors plan to release a detailed report on the procedure, but have not yet decided when and where it will be published.

In the meantime, Minnesota is being lined up against several possible mates. The species' current population is based on only 14 animals. The Przewalski's horse, native to China and Mongolia, is being reintroduced into the wild in small groups throughout Asia.