Zoo performs first reverse vasectomy on horse

This photograph released by the Smithsonian's National Zoo shows a Przewalski horse named "Minnesota" at the Smithsonian's National Zoo grazing in his yard on July 2, 2005. Recently, veterinarians at the National Zoo performed a successful reverse vasectomy on the animal - the first procedure of its kind to be performed on an endangered species. 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. (AP Photo/National Zoo, Ann Batdorf)

(AP) -- Scientists at the Smithsonian Institution's National Zoo have revealed they reversed a vasectomy on an endangered horse to allow it to reproduce naturally - the first-known operation of its kind on an endangered species.