Development and ultrastructure of bovine matured oocytes vitrified using electron microscopy grids

Area of Science:

• Reproductive biology
• Cryobiology
• Embryology

Background:

• Cryopreservation of cattle oocytes is crucial for assisted reproductive technologies.
• Optimizing vitrification protocols is essential to maintain oocyte viability and developmental potential.
• Previous methods have shown varying success rates and potential ultrastructural damage.

Purpose of the Study:

• To establish and validate a cryopreservation methodology for cattle oocytes using ultra-rapid cooling vitrification.
• To assess the quality of vitrified oocytes and subsequent in vitro produced embryos.
• To compare the developmental competence of vitrified-warmed oocytes with fresh controls.

Main Methods:

• In vitro matured cattle oocytes were vitrified using a minimum volume, ultra-rapid cooling technique.
• Oocytes underwent equilibration and vitrification in solutions containing ethylene glycol and sucrose.
• Warmed oocytes were assessed for viability, subjected to electron microscopy, and used for in vitro fertilization and embryo culture.

Main Results:

• Vitrification resulted in 75% viable oocytes post-warming.
• Embryo cleavage and blastocyst rates were 64.98% and 17.3% for vitrified oocytes versus 70.72% and 25.54% for controls (P < 0.05).
• Ultrastructural analysis revealed minor damages in vitrified oocytes, less severe than previously reported, with no significant differences in blastocyst cell number or dead cell indexes.

Conclusions:

• The developed ultra-rapid cooling vitrification technique effectively cryopreserves cattle oocytes.
• This method produces in vitro embryos with quality comparable to those derived from fresh oocytes.
• The technique offers a promising approach for cattle oocyte cryopreservation with minimal detrimental effects on developmental potential.