 Several American zoos also collaborated in breeding "E. f. przewalskii" from 1979 to 1982.Recent advances in equine reproductive science in the United States also have potential to further preserve and expand the gene pool.In October 2007, scientists at the Smithsonian Institution's National Zoo successfully reversed a vasectomy on a Przewalski's horse — the first operation of its kind on this species and possibly the first ever on any endangered species.