Equine embryo transfer has been used since 1970s and has increased in popularity over the years. Embryo transfer is a process that involves breeding a donor mare to a stallion and then transferring the resulting embryo at 7-8 days, into the uterus of a reproductively competent recipient mare, which carries the foal to term and raises it until weaning. For those mares that have difficulty even getting to the 7-8 day stage, or sub fertile stallions – ICSI (intracytoplasmic sperm injection) is now an option.
The resultant foal will be the genetic offspring of the donor mare and stallion.
Advantages
– allows donor to continue performance career while the recipient carries the foal.
– more than 1 pregnancy per year can be achieved from a single mare.
– foals can be obtained from mares that are sub fertile or cannot viably carry embryos themselves.
Disadvantages
– some breed registry societies have restrictions on the number of foals that can be registered per mare per season.
– extra vet expenses dependant on number of embryos/recipients needed if/when successful.
– more intensive management is required for donor and recipients.
The first step of the process is to synchronise the reproductive cycles of the donor and recipient mares. It is important that the recipient mare is at a similar stage in her cycle as the donor mare to ensure that her uterus is ready to accept the embryo.
The donor mare is bred to the stallion. Live cover, AI with fresh/chilled or frozen semen are all common methods. It is important that the mare is monitored, and the time of ovulation is known.
The flushing of the embryo is usually done at 7-8 days post ovulation. A sterile catheter is placed into the uterus of the donor mare and the embryo removed by flushing a special fluid into the uterus. The recovered fluid passes through a filter allowing the microscopic embryo to be retrieved. The embryo is then assessed and graded according to its appearance and then prepared for transfer. The embryo is then inserted into the recipient mare and a pregnancy scan is performed on the recipient mare 6-7 days following the transfer of the embryo.
Success Rates
A survival rate of 75-80% of good quality embryos recovered typically occurs following transfer. But it is also important to consider that embryo recovery rates may be as high as 75% or as low as 25%. There are many factors that influence the recovery rate including:
– age and fertility of donor mare
– quality of semen used
– day of recovery
– number of ovulations
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