Cryopreservation in equine embryos is the process of storing fertilised horse embryos or semen at extremely low temperatures (−196∘C) in liquid nitrogen to stop all biological activity for future use. The primary, most successful method is vitrification (or ultra-rapid freezing), which solidifies the embryo into a glass-like state without damaging ice crystals. It is used to preserve genetics, ship embryos worldwide, and manage breeding schedules for elite or aged mares.

Cryopreservation & Vitrification

What is Cryopreservation?

Requirements

Advantages

Successful equine embryo cryopreservation depends primarily on the timing of recovery and the quality of the embryo. For the best results, embryos should be small—ideally less than 300 micrometers—which usually requires flushing the donor mare early, around day 6 or 6.5 after ovulation. The embryo must be "Grade 1," meaning it shows no signs of degeneration or cellular debris under a microscope. Before freezing, the embryo is treated with cryoprotectants (like glycerol or ethylene glycol) to prevent lethal ice crystals from forming inside the cells. If a larger embryo is used, a specialised "collapse" procedure is required to remove internal fluid. Finally, the process requires specialised equipment, such as liquid nitrogen for storage and specific media to safely rehydrate the embryo after thawing.

The primary advantage of cryopreservation is the flexibility it offers breeders by decoupling the embryo collection from the need for a synchronized recipient mare. It allows for the long-term preservation of elite genetics, enabling a mare’s bloodline to be utilized years after her athletic career or even after her death. Additionally, frozen embryos significantly simplify international trade, as shipping a small straw is far more cost-effective and carries lower disease-transmission risks than transporting a live horse or a fresh embryo. This technology also allows owners to "bank" embryos during the peak of the breeding season and transfer them later at a more convenient time, optimising facility management and foal birth dates.