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Westvets Brisbane Veterinary Care

Embryo Transfer (ET)

What does the embryo transfer process involve?

Embryo transfer is when a very young embryo is flushed from the uterus of a donor mare to transferred to a recipient mare. The recipient mare than carries the foal to full term.

What are the advantages of doing an Embryo Transfer?

  • Donor mare can continue a performance career
  • Foals can be produced from mares that unable to carry a foal longer than 15 days of pregnancy
  • Allows more than one pregnancy from one mare during a breeding season
  • Younger mares can produce offspring
  • Obtain foals from mares foaling late in the breeding season thus enabling them to conceive earlier the following year

What are the steps in the Embryo Transfer Procedure

  • The donor and recipient mares must be synchronized in their reproductive cycles. We have a large number of recipient mares.
  • The donor mare is bred using either fresh, chilled or frozen semen. The ovulation time must be known and is monitored carefully with ultrasound scans.
  • 7-8 days following the detection of ovulation, the embryo if flushed using a specific fluid medium, a filtration system, and sterile technique. The fluid is than examined under the microscope to find the embryo. The embryo is graded and transferred into the mare.
  • A pregnancy scan is than performed on the recipient mare following the transfer of the embryo.

What is the success rate of ET?

  • The most important factors that affect the recovery rate of embryos are the timing of the insemination and the fertility of the donor mare and stallion.
  • Stallion fertility is further influenced by semen dose, quality, and method of preservation.
  • In young, healthy mares with no history of reproductive problems inseminated with fresh semen from fertile stallions, typical embryo recovery rates near 80%.
  • A survival rate of 75-80 % of good quality embryos recovered typically occurs following transfer.
  • This gives a 60-65% success rate per cycle and therefore it is recommended that you are prepared for 2 cycles per pregnancy from young fertile mares inseminated with fertile fresh semen.
  • A reduced embryo recovery rate occurs when aged mares (greater than 14 years), or those with a history of subfertility are used as donors, or when chilled, or in particular, frozen semen is used.

Can you transport Embryos?

We can manage your mare from insemination to transfer – or you can manage your own breeding with your vet and send either your mare to us for the flush and transfer procedure or the chilled embryo for transfer into one of our recipient mares. This requires very close communication between all parties involved.

Can you freeze Embryos (Embryo Vitrification)?

Vitrification or freezing of embryos is a relatively new technique that is an excellent way to preserve genetics.  In this process suitable embryos that are recovered are processed, frozen and stored in liquid nitrogen indefinitely.  They can then be thawed and transferred into a recipient mare when it is convenient. 

What are the advantages of freezing your horse’s embryos?

  • Storage of genetics in the event of loss of the mare;
  • Embryos can be collected at the end of the show season and transferred at a preferred date;
  • Late foaling mares can store embryos for transfer early in the following season.

Pregnancy rates following transfer of frozen-thawed embryos are slightly lower than fresh or chilled embryos.  Careful consideration should be made prior to deciding to freeze embryos versus using them fresh as there will be a lower pregnancy with each manipulation of the embryo.

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