Embryo Transfer (ET) is a collective term for the techniques used to transfer an embryo from a donor mare to another mare, the recipient mare. This process consists of two main elements: embryo flushing and embryo transfer.
Embryo flushing in horses is a technique used to recover an embryo from the uterus of a donor mare. This is done after the mare has been inseminated, typically on day 7, 8, or 9 after ovulation. During the flushing procedure, flushing fluid is introduced into the uterus. As it flows back out, it passes through a filter that captures the embryo.
The flushed embryo can then be transferred into the uterus of a recipient mare, who will carry the pregnancy and give birth to the foal.
Freezing or vitrification of equine embryos is now possible and is becoming increasingly common. This technique allows breeders to preserve embryos for transfer at a later time.
Embryo transfer is the process of placing an embryo, flushed from a donor mare, into a recipient mare.
The procedure for transferring the embryo into the recipient is similar to insemination with frozen semen.
The embryo is loaded into a straw and transferred into the uterus of the carefully selected recipient mare using a double guarded embryo transfer stylet.
Embryo Transfer (ET) offers breeders and horse owners many advantages, allowing them to make use of a mare’s genetic value without the mare having to undergo the risks of pregnancy herself.
The main benefits of ET include:
For mares actively competing, ET allows them to produce offspring without interrupting their performance schedule. This enables the mares to contribute to breeding without compromising their sporting careers.
ET helps reduce the medical risks associated with pregnancy and foaling for the (valuable) donor mare. She can continue to compete or stay active while contributing to breeding without the physical demands of carrying a foal. This is especially important for older mares or those with health issues, who may face increased risks during pregnancy. The embryos are transferred to young, healthy recipient mares, better able to cope with the challenges of pregnancy, birth and lactation.
Mares that have difficulty conceiving or have lost previous pregnancies may still produce embryos that can be carried by healthy recipient mares. This allows them to retain their value in breeding.
Mares that foal late in the season or are not pregnant can still provide embryos without having to carry another foal themselves. This gives breeders the option to keep the mare open for an early start in the following breeding season.
ET makes it possible for a mare to produce more than one foal per year, significantly increasing breeding capacity.
Embryos can be cooled and transported to the location of the recipient mare. Temperature-controlled shipping ensures that the embryos are stored and moved under the right conditions. A trained veterinarian can perform the transfer on-site.
To maximize success, the embryo should ideally be transferred as soon as possible, and certainly within 24 hours after flushing.
Embryo Transfer is therefore a highly versatile technique that helps preserve the health and performance of valuable mares, while optimizing breeding potential. At Equiception, we’re happy to guide you through the process and ensure the best care for both donor and recipient mares.
The choice of recipient mare plays a crucial role in the success of embryo transfer, the development of the pregnancy, and the growth of the future foal.
The importance of the recipient mare should not be underestimated. It is often assumed that her selection is less critical than other parts of the process, but the opposite is true. The right recipient mare can make the difference between a successful pregnancy and a failed embryo transfer. Careful selection is therefore essential to increase the chances of success and ensure the well-being of the foal.
Ideally, the recipient mare should closely match the donor mare in body type and size. The optimal age range is between 3 and 15 years, and the weight difference should not exceed 150 kilograms. Equiception offers a selection of high-quality recipient mares, but it is also possible to use your own mare as a recipient. We recommend discussing this option with your veterinarian to determine whether your mare is suitable for the role.
For more information, see our page on recipient mares.
At Equiception, you have the flexibility to choose whether your mare is inseminated by our veterinarians or by your own veterinarian. If you decide to bring your mare to us for insemination, she may leave our facility between insemination and embryo flushing.
Based on our extensive experience, we have found that the chances of recovering a viable embryo and achieving a successful pregnancy are often higher when the mare is inseminated and monitored by our own team, especially in cases involving fertility challenges.
If you prefer to have the insemination done by your own veterinarian, you still have the option to have the donor mare flushed at Equiception or by your veterinarian. However, it is essential that the exact day of ovulation is known.
Once ovulation has been confirmed, you must contact us by phone to schedule the embryo flush and/or reserve a recipient mare.
One of the great advantages of embryo transfer (ET) is that mares can continue their sport careers and still produce foals. However, in some cases, it may be necessary to adjust the mare’s training or competition schedule to improve the chances of success.
Exercise, heat (including heat from movement), and stress (such as during transport) can affect the mare’s fertility. This is especially important to consider if a mare does not produce embryos after several attempts, even though there are no other fertility problems.
To give the embryo the best chance, owners may need to make some changes. This might include stopping training or competitions for a short time, especially around ovulation and between insemination and embryo flushing.
That said, many mares do produce embryos successfully while continuing with sport and travel. This is very positive, but it’s important to have realistic expectations. Not all mares respond the same way, so careful planning and flexibility are key when combining sport and breeding.
Pregnancy rates per cycle in embryo transfer depend on several factors. These include both the chance of recovering an embryo during flushing and the chance of achieving a successful pregnancy in the recipient mare after the transfer. For the best results, it is important that both donor and recipient mares are well managed, and that the flushing and transfer procedures are carried out with care and expertise.
The chance of recovering an embryo can vary significantly per cycle. It depends on the fertility of both the donor mare and the stallion, as well as the type of semen used (fresh, chilled, or frozen). The chance of pregnancy after the embryo is transferred also varies. This depends on the quality of the embryo, the skill of the person performing the transfer, and the health and suitability of the recipient mare.
It’s also important to keep in mind that about 8 to 10% of mares lose the pregnancy after the first positive check. This rate is similar for both recipient mares and mares carrying their own foal, but it may be slightly higher when the embryo comes from an older donor mare.
At Equiception, we achieve an average pregnancy rate of 75% for embryos transferred into our own recipient mares. However, results can vary throughout the season, and pregnancy rates often drop during periods of high temperatures.
Yes, flushed embryos can be successfully vitrified. The vitrification process is a valuable technique that is being used more and more frequently. However, it is not a simple procedure, and its success depends on factors such as the size of the embryo and the exact timing of vitrification.
Smaller embryos (under 300μm) can be vitrified successfully and later used to achieve pregnancy in a mare. Timing is critical, as the embryo reaches the uterus around day 5.5 after ovulation. To ensure the embryo is still the right size, flushing must be done early on the 7th day after ovulation. At this stage, the embryo grows rapidly, so even a few hours’ delay can mean the difference between a suitable embryo and one that is too large for successful vitrification.
Larger embryos, flushed on day 8 or 9 after ovulation, must be reduced in size before vitrification. This is done using specialized lab equipment, including a micromanipulator, to handle the embryo very carefully. This technique requires a high level of skill and precision, as even a slight delay can result in the embryo growing too large to vitrify effectively.
Vitrifying embryos offers breeders great flexibility, as the embryo can be stored and transferred at a later time, especially helpful when waiting for the right recipient mare to become available.
With repeated inseminations and embryo flushes, especially from the third to fifth cycle, the likelihood of uterine infections in the donor mare can increase. These mares may accumulate fluid in the uterus, show inflammatory cells on cytology, and reveal bacterial growth in cultures. That’s why it is essential to closely monitor the uterine health of the donor mare, so that any necessary treatment can be started in time to prevent complications.
In addition, there is always a small but serious risk of rectal tears during any rectal examination. Although rare, such tears can lead to severe or even life-threatening complications. Depending on the size, severity, and location of the tear, surgical treatment may be required. The prognosis depends on how severe the tear is, how quickly it is treated, and the quality of the initial care provided.
At Equiception our experienced veterinarians perform rectal examinations with great care and attention. Young, inexperienced, or nervous mares are sedated to ensure the safety of both the mare and the procedure.
The cost of ET at Equiception depends on several components of the procedure. This includes the flushing of the donor mare, the transfer of the embryo to the recipient mare, required medication, and boarding fees for the mare(s) during the process. Additional costs may apply for the transport of the embryo and/or rental of a recipient mare.
The choices made throughout the process will influence the total cost of the procedure.
For the most up-to-date prices, please refer to our price list.
