THE PRODUCTION OF RUMINANT EMBRYOS INVITRO

The potential for dramatic increases in genetic gain, and the production of transgenic animals with highly desired production, and disease resistance characteristics through DNA transfection techniques, in pronuclear oocytes and embryonic stem cells, and nuclear transplantation for embryo multiplication and transfer (EMT) has resulted in increased research or the production of embryos in vitro. The primary techniques which are essential for embryo production are maturation of oocytes in vitro (IVM), in vitro fertilization (IVF) and embryo culture in vitro. Combining these techniques enables the large scale production of mature and fertilized oocytes for the introduction of genes, embryos for the production of embryonic stem cells and embryos for transfer, and oocytes and embryos for EMT. There is considerable margins available to improve the efficiency of IVM, IVF and embryo culture techniques. While the majority of oocytes will undergo nuclear maturation by culture in medium containing LH, FSH and oestrogen or oestrus serum, their complete nuclear maturation and viability need to be improved. There are problems for achieving fertilization in vitro for many desirable sires and this needs to be solved by determining universal sperm capacitation techniques. Embryo culture is still apparently sub-optimal although some reports indicate that in vivo fertilized embryos can be cultured without a dramatic loss of viability. It is possible to produce dramatic improvements in the production capacity for ruminant embryos by relatively simple adjustments to technique but further improvements may require more basic research to ascertain the cellular physiology of gamete maturation, fertilization and early embryonic development.