Last Updated on May 17, 2020 by Allison Price
Embryo transfer is used to procure offspring from mares with decreased reproductive capacity. (Mares with undiagnosed subfertility, uterine pathologies, or simply older mares)… or from quality mares which must remain pregnant to remain competitive.
A good ET outcome includes intensive management of both donor and recipient mare. While this technology has been used in the cattle industry since the 1970s… the horse breeder and breed registries have only recently adopted this technology.
Many breed societies allow for the identification of foals conceived by embryo transfer. Through number, it now allows the identification of foals delivered in the same year. Because of this… several horse breeders got many foals from a single donor mare in one breeding season.
Embryo transition has both benefits and drawbacks as in other management strategies. Work is continuing on the handling and freezing of equine embryos. You can also transport or store embryos for long distances.
| Advantages | Disadvantages |
| Boost yearly breeding rates in superior mares | The maximum allowable number of foals registered each year or for a lifetime (restrictions on breed registration) |
| Mares will continue his career on excellence | High prescription costs, veterinarian fees, mare treatment, research fees, registration fees |
| Get foals from the issue and aged mares | Intensive donor and recipient mare care, and recipient herd maintenance |
| Immature ages 2 yrs. make foals | Just one embryo each cycle (The mare cannot be superovulated) |
Selection of the Donor Mare
Sub fertile Mares
Because ET is costly, careful selection of the donor mare is necessary. Embryo transfer does not fix oocyte quality-related infertility problems (age mares). It can’t fix mares with oviduct blockage or dysfunctions. Mares that have repeated unaccounted for abortion are strong candidates for ET.
Superior Mares
Genetically superior mares may be chosen for ET. They may have more than one foal per year depending on the criteria of breed registry. You can also breed a mare to multiple stallions during one breeding season. It produces foals from each of the breeding. It is also common for a mare to get a foal by ET early in the season and then breed later to bear her own foal.
Seeing as performance mares need only take 1-2 weeks off to donate an embryo for ET… they are now becoming the type of selected mare for ET.
Embryo Transfer: The Procedure
You can deliver embryos non-surgically or surgically into the recipient mare. The method is a standing flank incision with local anesthesia. Place the embryo into the uterine horn by puncturing the horn. The more popular technique is a transcervical, non-surgical transfer. Dilate the cervix using a finger, and the pipette of the ET transfer passes through the cervix into the uterus. Be careful to avoid the finger from going into the uterus- only the pipette can go into the uterus. If you use sheath protection until the pipette is in the cervix, the pregnancy rate should increase.
Here is the basic ET drill:
1. At the time of ovulation, the donor mare’s inseminated with frozen semen from a stallion. This will create an embryo.
2. At the age of 8 days, the embryo’s flushed out of the uterus of the donor mare. It’s placed in an appropriate surrogate mare which carries the pregnancy to the full term.
Traditional Procedure:
Synchronizing Cycles
One of the most critical elements of a successful embryo transfer procedure is synchronizing the cycles of the two mares… The donor (who provides the embryo) and the recipient (who carries the pregnancy to term). It’s essential that the uterus of the receiver mare be ready to receive and nourish the embryo.
Freezing and Thawing Challenges
One alternative, after an embryo, is retrieved by the practitioner… They use a procedure called vitrification to preserve it… instead of moving it to a recipient mare. That yields many advantages. Equine embryos, unfortunately, do not withstand in frozen places as do other animals. Modern freezing actually results in a pregnancy rate of about 25 percent… as opposed to a pregnancy rate of 80 percent following fresh embryo transfer.
Fact:
At present, the vitrification cycle yields a pregnancy / live foal average of 70 percent. Vitrification converts the liquid around the embryo to a glass-like solid, to avoid ice formation. They collapse a 7- or 8-day-old embryo before storing it in liquid nitrogen to drain much of its blood. After thawing and going through a series of fluids. The collapsed embryo regains its natural form and fluid volume. This, though, is expensive.
New Advance Procedure: ICSI and IVF
Applied uses of ET have evolved with the growth of other reproductive technologies. Any of those requirements include:
- Genome preservation (Przewalski’s horse)
- Obtaining pregnancy from older mares
- Permitting mare to reproduce during competition
- Enable a late foaling mare to remain open for the next season’s early breeding
- Connected with other advancements including sexed sperm, ICSI, cloning, et
Intracytoplasmic sperm injection (ICSI)
The scientists take a single sperm and inject it into the mature oocyte in a lab. Then offering oocyte aspiration from the ovaries using an ultrasound-guided needle. Rather than waiting for release at ovulation.
Although only one or two oocytes may be mature enough to ovulate at a time… veterinarians may recover multiple immature oocytes in a single aspiration for maturation. When fertilized, approximately 20 percent grow into embryos that you can transfer. With a current pregnancy / live foal rate of 65 percent after transfer. If multiple embryos are produced from one aspiration… breeders of the ICSI procedure may pass these embryos to recipient mares.
ICSI embryos have a significantly higher early failure rate. 20% in the first 30 days compared to 10% in typical embryo transfers. It is possible due to the many steps involved. Developing and transferring that embryo outside of a natural uterine environment.
Oocyte aspiration can also lead to complications such as:
Infection, hemorrhage, or adhesion formation.
While these risks are low, it’s still important to keep them in mind. You should reserve ICSI for mares that are unable to carry out embryo transfer on. Or when sperm supply is poor.
In vitro fertilization (IVF)
Is the process of placing the sperm and egg together in a laboratory culture? Eventually allowing them to fertilize in a natural way. This procedure reduces the need for the lengthy time that ICSI requires.
While IVF success rates in human medicine have made the approach practically commonplace for infertility treatment… it’s still quite challenging in horses. In a research lab, equine sperm and egg don’t seem to align well, and embryos have low survival rates when they do.
Embryo Transfer: How Much Does It Cost?
Donor mare owners have the option to lease or to buy the recipient mare. Leasing is the most common option. A non-returnable, non-transferable entry fee of $600 to $1,500 is due upon contract signing. This fee will cover the costs for synchronizing a recipient mare. For three to four and sometimes unlimited embryo flushes.
The leasing fees vary between $2,600 and $4,200. After the recipient mare’s confirmed in foal, the donor mare owner will be responsible. Paying her boarding fees and veterinary expenses.
The following may cost you additional fees:
- Additional flushes subjected to the contract specifics and may require extra fees.
- Failure to return the recipient mare will result in a penalty fee.
- Mare maintenance.
Vitrification costs $600-750 per embryo.
Total Expense May Cost You: $4000 – $6000
