The present invention provides porcine CMP-N-Acetylneuraminic-Acid Hydroxylase (CMP-Neu5Ac hydroxylase) protein, cDNA, and genomic DNA regulatory sequences. Furthermore, the present invention includes porcine animals, tissues, and organs, as well as cells and cell lines derived from such animals, tissues, and organs, which lack expression of functional CMP-Neu5Ac hydroxylase. Such animals, tissues, organs, and cells can be used in research and in medical therapy, including in xenotransplantation, and in industrial livestock farming operations.