Once the oocyte has been injected with a sperm cell and it has developed into an embryo, it is only viable for so long unless it is frozen. Freezing it gives owners time to form a plan for their embryo, frozen embryos can be stored indefinitely, resulting in better timed foaling
Vitrification is very important for the embryo, so that it stays viable for transfer. It also allows for harsher screening of recipient mares
