In vitro fertilization and development of frozen-thawed bovine oocytes

Area of Science:

• Veterinary Science
• Reproductive Biology
• Cryobiology

Background:

• Cryopreservation of bovine oocytes is crucial for assisted reproductive technologies.
• Evaluating different cryopreservation methods and developmental stages is essential for optimizing success rates.

Purpose of the Study:

• To compare the efficacy of slow freezing (S-oocytes) versus vitrification (V-oocytes) for bovine oocytes.
• To assess the impact of cryopreservation at the germinal vesicle (GV) stage versus after in vitro maturation (IVM) on oocyte survival and developmental potential.

Main Methods:

• Bovine oocytes were cryopreserved using slow freezing or vitrification at either the GV stage or post-IVM.
• Survival was assessed morphologically, followed by in vitro fertilization (IVF) and embryo culture.
• Embryo development to morula and blastocyst stages was evaluated.

Main Results:

• Slow freezing yielded higher morphological survival rates (30.7% at GV, 53.3% post-IVM) than vitrification (14.6% at GV, 14.0% post-IVM).
• Fertilization rates were highest for post-IVM S-oocytes (51.0%) compared to other cryopreservation groups, though lower than unfrozen controls (75.8%).
• Embryonic development to morula/blastocyst stages was achieved from post-IVM S-oocytes (1.6%), leading to a successful pregnancy and twin calf birth after embryo transfer.

Conclusions:

• Slow freezing of bovine oocytes after in vitro maturation is a viable cryopreservation strategy.
• This method demonstrates superior developmental competence compared to vitrification and freezing at the germinal vesicle stage.
• Successful live birth confirms the potential of slow-frozen, in vitro matured oocytes for bovine reproduction.