Vitrifying expanded equine embryos collapsed by blastocoel aspiration is less damaging than slow-freezing.

This paper focuses on understanding the more efficient method of cryogenically preserving equine embryos that are larger than 300 μm. It found that slow-freezing proved more damaging than vitrification after the embryos had their fluid withdrawn.

Study Overview

• The study’s objective was to compare the effects of two cryopreservation methods, slow-freezing and vitrification (rapid freezing), on equine embryos that had undergone a procedure to remove fluid from their blastocyst (a structure formed in the early development of mammals).
• Embryos used were grade 1 blastocysts gathered 7 or 8 days post ovulation and measured more than 300-550 μm, with others exceeding 550 μm.
• Post cryopreservation, these embryos were cultured for 24hours at 38 °C to assess their re-expansion and were then graded and measured.
• Control embryos were similarly cultured for 24 hours, without undergoing cryopreservation or being exposed to cryoprotectants.

Approach

• The researchers divided the embryos into two groups: the first group underwent slow-freezing in a 10% glycerol solution while the second group was vitrified in a solution of 16.5% ethylene glycol, 16.5% DMSO, and 0.5 M sucrose.
• To gauge the quality of the embryos, they were stained to measure live/dead cell proportion, cytoskeleton quality, and capsule integrity.

Findings

• The experiment showed that the quality grade and re-expansion of the 300-550 μm embryos were compromised after slow-freezing but were unaffected by vitrification.
• For embryos larger than 550 μm, slow-freezing resulted in additional cell damage, illustrated by a significant increase in the proportion of dead cells and disruption of the cytoskeleton. These changes were not observed in vitrified embryos.
• Neither of the freezing methods significantly affected the loss of the capsule.

Conclusion

• The research concluded that slow-freezing of expanded equine blastocysts, after collapsing by aspiration of blastocoel fluid, compromises the post-thaw embryo quality more than vitrification.
• Thus, for equine embryos that have undergone fluid removal from the blastocoel, vitrification is less damaging for cryopreservation than slow-freezing.