Freezing embryos has several potential benefits, including:
- The ability to preserve genetic material from a specific stallion-mare cross
- Decreased cost of transport of embryos compared to a live horse
- Decreased number of recipient mares required
Due to the nature of the mare's reproductive physiology, super-ovulation is not an efficient process compared to other species, such as cattle and sheep. In the majority of embryo collection attempts, the mare will ovulate a single follicle and, as a result, only one embryo is usually available.
This technology is evolving and at this stage, only small equine embryos have been successfully frozen.
In order to collect small embryos, the flush of the donor mare must be performed during a very narrow window of time relative to embryonic development. The embryo collection attempt must be performed approximately 6.5 days after ovulation in order to have an opportunity to collect an embryo that will be small enough to freeze.
Embryos are exposed to specific concentrations of cryo-protectants prior to freezing. The cryo-protectants help to remove water from within the cells of the embryo and consequently help the cell survive the freezing process.
Once collected, the embryo is loaded into a plastic straw and stored in a tank of liquid nitrogen.
Transfer into a recipient mare involves thawing or 'warming' the straw containing the embryo.
Due to the complex nature of the procedure, pregnancy rates following transfer of frozen-thawed embryos is somewhat less than that achieved with transfer of a 'fresh' embryo.