Vitrification of Immature and Mature Bovine Oocytes
Vitrification is the latest technique used in cryopreservation, the ability to utilize this method with oocytes and embryos has become a valuable system. Vitrification has been successful with bovine embryos and oocytes but is far from optimal. Following cryopreservation storage discarding embryos can cause ethical issues, and mature oocytes have fragile organelles that can be detrimentally affected by ice crystal formation during freezing. Immature oocytes have not formed some of these temperature sensitive microfilaments and can circumvent these detrimental effects. The common intracellular cryoprotective agents are dimethyl sulfoxide, glycerol and ethylene glycol. Different combination of these agents have been reported for vitrification of oocytes. The overall objective of this experiment was to determine if immature and mature cumulus cell complexes vitrified in solutions of dimethyl sulfoxide or glycerol in combination with ethylene glycol would be competent to produce pronuclei following thawing and in vitro fertilization. Two experiments evaluated two cryoprotectant solutions and their ability to fertilize bovine cumulus cell complexed oocytes (n=400). The first study used DMSO and glycerol containing vitrification solution with immature bovine oocytes (n=200) followed by IVM and IVF with an end point of pronuclei formation to indicate fertilization. The second used DMSO and glycerol containing vitrification solutions with mature bovine oocytes (n=200) followed by IVF. We found that vitrifying immature oocytes with DMSO or Glycerol containing solutions prior to IVF resulted in higher fertilization for DMSO P<.01. Vitrifying mature oocytes with DMSO or glycerol containing also resulted in higher fertilization for DMSO solution P<.05. These results suggest that DMSO may be the more appropriate choice when used in combination with ethylene glycol for vitrification of immature and mature oocytes.