The invention relates to the genetic manipulation of non-human animals. More particularly, the invention relates to genetic manipulation of non-human animals to be used for xenotransplantation. The invention provides viable gene knockout swine including swine in which the .alpha.(1,3)-galactosyltransferase gene has been disrupted, methods for making such swine, and methods of using the tissues and organs of such swine for xenotransplantation.