Cloning research. Cups containing cow ovaries 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.