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.