Post thaw quality and viability of vitrified immature sheep oocytes using different cryoprotectant concentrations

• Published in: Cryo-Letters Vol. 42; no. 6; p. 321
• Main Authors: Sofi, K A, Qureshi, B, Shah, A, Fazili, M R
• Format: Journal Article
• Language: English
• Published: England 01-11-2021
• Subjects: Animals; Cryopreservation - methods; Cryopreservation - veterinary; Cryoprotective Agents - pharmacology; Ethylene Glycol - pharmacology; Oocytes; Sheep; Vitrification
• ISSN: 0143-2044

The cryopreservation of oocytes through vitrification is quite successful but oocyte vitrification is still being standardized because of their structural and molecular sensitivity to the cooling and freezing processes.
To evaluate the effect of different cryoprotectant concentrations on post-thaw morphology and viability of immature oocytes in sheep.
Vitrification was achieved in three vitrification solutions comprised of different concentrations of the cryoprotectants ethylene glycol + DMSO, viz., (G1) 20%, (G2) 30%, (G3) 40% ethylene glycol + DMSO in equal ratio. Cryopreservation was in open pulled straws. Post vitrification evaluation was done after 1 week's storage in liquid nitrogen based on morphological evaluation and viability using trypan blue dye.
The present study revealed non-significantly higher morphologically normal oocytes in G3 (74.7%) followed by G2 (70.3%), and the lowest in G1 (66.6%). Morphological defects were observed in 33.3 %, 29.6% and 25.2% of oocytes after cryopreservation in 20% (G1), 30% (G2) and 40% (G3) vitrification solutions, respectively. The results were non-significantly different between vitrification solution groups. However, the viability of post thaw immature oocytes was 95.6%%, 84.4% and 81.1% after vitrification in G1 (20%), G2 (30%) and G3 (40%), with viability being significantly highest (P<0.05) in G1 (20%) and lowest in G3 (40%).
Cryoprotectant concentrations enable the maintenance of normal morphology and minimize cryoinjury during vitrification of immature oocytes.