New device for the vitrification and in-straw warming of in vitro produced bovine embryos

Two experiments were designed to test the use of a new device designed to vitrify and in-straw warm in vitro produced (IVP) embryos, which can potentially be used for their direct transfer to recipient females in field conditions. In experiment 1, IVP embryos from both prepubertal and adult animals were vitrified on cryotops and warmed in steps (1, 0.5 and 0M sucrose; protocol W3) or directly in 0.5M (protocol W1/0.5) or 0M sucrose (protocol W1/0). Similar survival rates were recorded 24h after warming for calf embryos irrespective of the warming procedure (W3: 79.2%, W1/0.5: 62.5%, W1/0: 66.7%). For cow embryos, survival rates at 24h post-warming were significantly higher when embryos were warmed using the W3 (85.7%) or W1/0.5 (89.1%) protocols compared to the W1/0 protocol (70.5%). In experiment 2, IVP embryos were vitrified on the new designed device followed by their in-straw cryoprotectant (0.5M sucrose) dilution/warming and different warming temperatures (45, 50, 60 and 70°C) were tested. When warming solution passed through the new vitrification/warming device at 45°C, 61.5% of blastocysts were fully re-expanded or hatched at 24h post-warming, being not significantly different to the control (65%). Other warming temperatures triggered significantly lower survival rates at 24h post-warming. No significant differences were detected in total cell numbers and blastocyst apoptosis indices in response to vitrification followed by warming at 45°C respect to the control. Our findings indicate that the new device allows vitrification and in-straw warming of IVP bovine embryos, being a useful option for their direct transfer in field conditions.