The Ins and Outs of Embryo Transfer
- November 26, 2025
By Monica Morganti Dr Med Vet DACT DECAR MRCVS, Senior Resident Stud Vet at Twemlows Stud Farm
For many mare owners, the dream is simple: keep your horse in competition while also producing the next generation of stars. In the past, that wasn’t possible as if your mare was in work, she couldn’t have a foal. But thanks to Embryo Transfer (ET), you don’t have to choose between competing or breeding. This clever technique means your mare can stay in her competitive career while a surrogate mare carries and raises her foal.
Not only does ET enable mares to breed before their natural fertility starts to decline, it also offers a way to preserve bloodlines, produce multiple foals from one mare, and to breed from mares who otherwise couldn’t safely carry their own foal to term.
So, how does it work and is it right for you? We put the most common questions to the experts.
What is Embryo Transfer?
Embryo Transfer is a breeding technique where your mare is inseminated, and about a week later her embryo is “flushed” out of the uterus. That embryo is then placed into a carefully synchronised recipient mare, who will carry the pregnancy to term and rear the foal until weaning.
First performed successfully in the 1970s, ET is now the most popular advanced breeding method for horses, used worldwide by sport horse breeders and owners who want to make the most of their mares.
What are the Benefits of Embryo Transfer?
There are several big advantages to choosing ET rather than having your mare carry her own pregnancy. These include:
For mares who can conceive but can’t carry a foal safely – some mares suffer from injuries, physical limitations, or reproductive conditions that make it risky or impossible for them to carry a pregnancy to term. ET allows their genetics to live on without putting their health in danger.
Multiple foals from one mare in a season – because embryos can be flushed more than once, it’s possible to produce two or more foals from the same mare in a year. Those foals can even be by different stallions, fast-tracking your breeding programme.
Don’t wait until retirement – many top-class mares spend their prime years competing. If you wait until the end of a long competition career, her fertility may already be in decline, making breeding difficult or impossible. ET lets you capture her best genetics while she’s still young and fertile, without pulling her out of work.
How do I Know if my Mare is Suitable for Embryo Transfer?
Almost any mare can be considered for ET, but results are best in young, healthy mares with no reproductive issues. Older mares or those with fertility problems can still be tried, though success rates may be lower.
Before starting, your vet will usually carry out a breeding soundness exam to check your mare’s reproductive health, considering her bloodlines as well as her physical soundness. As with all breeding it is essential to carefully select the correct stallion, to complement your mare’s features.
Recipient mares are equally important. They should be healthy, fertile and of a similar size to your mare, with a kind, steady temperament. Some studs, such as Twemlows Stud Farm will be able to provide recipient mares for you.
What is the Embryo Transfer Process?
The ET process is straightforward and painless for your mare:
1. She is inseminated, just as in artificial insemination.
2. Seven to eight days later, the embryo is flushed from her uterus.
3. The embryo is found and examined under a microscope before being transferred into the recipient mare.
4. About a week later, the recipient is scanned to hopefully confirm a pregnancy.
For many cases, your mare will not need to stay at the stud and can visit on a “walk-in” basis. As it is a non-surgical procedure it can usually fit around competition schedules with minimal disruption. Transported ET can also be facilitated – this is when you breed and flush your mare at home with your own vet and send the embryo to stud to be placed in the recipient mare.
When is Embryo Transfer Best Carried Out?
ET works best during the natural breeding season – spring through summer, when mares are cycling normally. With some clever management, such as extended daylight using yard lighting, the season can be brought forward to start in early spring. There are further advanced reproductive techniques that can retrieve eggs from your mare in winter. These eggs can be used to create embryos in vitro (IVF/ICSI) that can then be frozen in liquid nitrogen where they can be preserved for many years. During the following breeding season, the embryos can be warmed and transferred into a suitable synchronised recipient mare.
Will I have to Stop Riding my Mare?
Not usually. Many mares continue in full training and competition while taking part in ET, particularly when using “walk-in” or transported embryo services. Some owners choose to give their mare a short break during insemination and flushing, but in many cases, riding can carry on as normal.
How Much Does it Cost and What is the Success Rate?
The cost depends on the route you take and whether your mare stays at stud, walks in for procedures, or uses transported embryos. There will also be additional expenses for scans, semen, and recipient mare hire.
Success rates are encouraging but not guaranteed. In a young, fertile mare inseminated with good-quality semen, embryo recovery rates are around 50–80% per flush. Older mares and frozen semen can reduce those odds.
What are the Pros and Cons of Embryo Transfer vs Carrying her own Pregnancy?
Pros of ET:
• Your mare can keep competing
• You can breed multiple foals from one mare in the same year
• Offspring can be sired by different stallions in the same year
• Preserve valuable genetics, even from mares who can’t carry a foal themselves
• Flexibility to use international or frozen semen from stallions worldwide
Cons of ET:
• More costly and management-intensive than carrying her own pregnancy
• Success rates vary, especially in older or subfertile mares
• Relies on access to recipient mares and specialist facilities
• More planning needed, so it’s not something to do on a whim
In Summary
Embryo Transfer is a proven, widely used breeding technique that gives mare owners the chance to combine performance with reproduction. It isn’t the cheapest or simplest breeding method, but with planning, the right team, and realistic expectations, it’s a brilliant way of combining sport and breeding without compromise.
For those with a mare worth breeding from but too valuable to take out of work, ET can be the perfect solution.
