The increased knowledge of endocrinology, cytobiology and embryology has also made stock farmers familiar with biotechnology. The genetic potency of both male and female animals may be utilised to better advantage today. However, the normal reproductive capacity, present in the form of large numbers of sex cells in female animals, is not utilised to an optimum extent. In spite of all recent developments so far, ninety-nine per cent of all ova are still lost. Since 1987, it has become possible to obtain immature ova from the living animal and to let them mature, fertilize and develop into embryos capable of transplantation outside the body. It may be expected that, in the long run, the number of embryos per excellent animal will show an enormous increase when this method is used. In addition, in vitro maturing of ova may be used in cloning embryos. This requires a large number of mature egg cells which act as recipients of the nuclei of embryonic cells, after the nuclei have been removed from these ova. One nucleus of an embryonic cell in each denucleated mature egg cell. These embryonic cells may be derived from an embryo which has disintegrated into individual cells or from an embryonic cell culture (embryonic stem cells). The only condition is that these cells have not yet become differentiated and have retained their omnipotent character.