Embryo collection in equines is a reproductive technique used to obtain embryos from a donor mare for transfer into recipient (surrogate) mares.

This allows a valuable mare to produce more offspring in a single breeding season than she would by carrying every pregnancy herself, and it enables breeders to preserve or distribute genetics if the mare might have complications during pregnancy.

Key points

Purpose:

  • Increase the number of foals from a valuable donor mare in one season.

  • Preserve genetics from older or performance mares.

  • Facilitate international or long-distance breeding without transporting the mare.

  • Allow a mare to continue athletic careers while producing foals.

    Overview of the procedure

    1. Synchronization: Donor and recipient mares are hormonally synchronized so the recipient’s uterus is at the correct stage to accept a transferred embryo.

    2. Ovulation and breeding: The donor mare is monitored and bred (natural cover or artificial insemination) when she ovulates.

    3. Flushing (collection): Typically 6–8 days after ovulation, the uterus of the donor is flushed with sterile fluid under sedation to recover the embryo. The procedure is usually performed standing and takes 15–30 minutes.

    4. Evaluation and handling: Recovered fluid is examined under a microscope to locate the embryo. Found embryos are washed and evaluated for quality, then either transferred fresh to a synchronized recipient or cryopreserved for later use.

    5. Transfer: The embryo is placed into the recipient mare’s uterus; pregnancy is checked by ultrasound about 10–14 days after transfer.

    Timing and stages

    • Embryos are usually collected 6–8 days post-ovulation; at this time, the equine embryo is a free-floating spherical blastocyst.

    • Successful transfer requires tight synchronization, generally within a day either way.

    Success factors and limitations

    • Donor age and fertility, embryo quality, timing of collection and transfer, and recipient health all affect success.

    • Typical pregnancy rates per transfer vary widely but often range from 50–70% with experienced clinics.

    • Multiple collections from one cycle are not feasible; repeated collections are done across cycles.

    • Not all embryos survive freezing; fresh transfers usually have higher success rates than frozen-thawed transfers, though freezing techniques have improved.