Successful vitrification of day-6 sheep embryos

Area of Science:

• Reproductive Biology
• Cryobiology
• Embryology

Background:

• Cryopreservation of mammalian embryos is crucial for livestock breeding and conservation.
• Vitrification offers a promising alternative to slow freezing, minimizing ice crystal formation.
• Optimizing vitrification solutions and protocols is essential for high embryo survival rates.

Purpose of the Study:

• To evaluate the efficacy of different vitrification solutions (VS1, VS11, VS14) for day-6 sheep embryos.
• To determine optimal pre-treatment protocols to mitigate osmotic damage during vitrification.
• To assess the in vitro and in vivo viability of vitrified sheep embryos.

Main Methods:

• Sheep embryos at day 6 of development were vitrified using three solutions: VS1, VS11, and VS14.
• Embryos were exposed to varying dilutions of VS11 (20-50%) at room temperature before vitrification.
• Survival rates were assessed in vitro and after transfer to recipient ewes.
• Pregnancy rates were recorded in recipients carrying vitrified embryos.

Main Results:

• VS1 vitrification resulted in 0% survival.
• VS11 vitrification showed high in vitro viability but poor in vivo survival initially.
• Pre-treatment with 30% VS11 significantly improved in vitro survival to 88.2%.
• Post-transfer survival rates were 55% for morulae and 62% for blastocysts after 30% VS11 pre-treatment.
• A pregnancy rate of 79% was achieved with recipients receiving two vitrified embryos.
• VS14 vitrification yielded 100% in vitro and 50% post-transfer survival in a small study.

Conclusions:

• Vitrification protocols, particularly with VS11 and appropriate pre-treatment, can achieve high survival rates for day-6 sheep embryos.
• Optimized vitrification solutions and step-wise exposure can overcome osmotic challenges.
• Successful cryopreservation of sheep embryos has significant implications for assisted reproductive technologies in sheep.