Cloning research. Forceps holding a cow ovary for use in cloning research. Ovaries from domestic cows (Bos taurus) are the source of oocyte cells needed to carry donor genetic material to create a clone. Once an oocyte has been extracted from an ovary and has been matured, its nuclear material is removed. The empty oocyte is filled with nuclear material from a body (somatic) cell of a donor animal. The resulting cloned oocyte is cultured to the blastocyst embryo stage before being implanted into a foster cow for pregnancy. Clones of valuable domestic cows and the gaur (Bos frontalis), an endangered species related to the cow, have been created by this method.