One of the most important components of a successful embryo transfer is the recipient mare.

Recipient mares should be between 3 and 15 years of age and within a 150kg weight range of the donor mare, in good physical condition and easy to handle. A potential recipient mare should be critically evaluated before making the decision to use her as a surrogate. A general physical examination should be performed, followed by a thorough reproductive evaluation to determine if the mare has any condition that may affect her ability to become pregnant after transfer or prevent her from carrying a foal to term. Recipients may receive 2 or maximally 3 embryos in a given year. If they fail to come pregnant or keep a pregnancy after these 2 or 3 opportunities, they should no longer be used as embryo recipients.

Equiception owns a large number of quality recipient mares that have all been critically evaluated before making the decision to use them as surrogates. These mares are available as surrogate mares for the embryos from our clients’ donor mares. It is not unusual, however, for clients to want to use their own mare(s) as the recipient of their donor mare’s embryo. This is understandable and can be an acceptable option, but it is recommended to discuss this with your own veterinarian to decide if the mare would make a suitable surrogate.

Equiception will not be held accountable for the possible consequences of using a less than ideal client-owned recipient mare.

Equine embryos can be frozen/vitrified successfully, however this is not a straightforward procedure and because of the significant challenges involved Equiception does not currently offer this service.

Only small equine embryos (<300μm) seem to be able to be frozen and then successfully used to impregnate a mare. Using frozen larger embryos is not seen as a viable technique as it has resulted in low pregnancy rates. Yet managing mares to recover embryos when they are <300μm requires accurate timing of ovulation so that an early flush is performed for embryo recovery exactly 6.5 days later. The equine embryo leaves the oviduct and enters the uterus around day 5.5. However, embryos that have a delay in entering the uterus may not be retrieved with a flush on day 6.5 and are subsequently missed. However, a second flush may be performed on the mare several hours later. Adding to what is already a difficult task is the rapid growth of an equine embryo at this stage of development. Even being 8-12 hours late with a flush can be the difference of recovering an appropriately sized embryo versus one too large to freeze.

Given the very small window to perform these early flushes, Equiception is not able to logistically perform them for clients.

The larger embryos, which are regularly flushed on days 7 to 9 post-ovulation, need to be ‘collapsed’ prior to the freezing process. This technique has been developed in the laboratory using microscopes with manipulators, embryo holding capabilities, and specialised drills to make small holes in the embryo. Successful operation of this equipment requires considerable expertise.

The ET pregnancy rate per donor mare cycle is dependent on both the embryo collection rate and the recipient pregnancy rate after transfer. In order for the whole process to be successful, management of the donor and recipient mare must be optimal and the techniques of both embryo collection and transfer well understood.

The embryo collection rate can vary significantly per cycle, depending on the fertility of the donor mare and stallion and whether fresh, transported chilled or frozen semen is used. The recipient pregnancy rate after transfer can also vary, depending on the quality of the embryo, factors associated with the recipient mare and the experience of the person performing the transfer. It is also important to be aware that there is an 8 to 10% chance of pregnancy loss after first detection of pregnancy, this rate being similar between embryo transfer recipient mares and mares bred to carry their own pregnancy. However, pregnancy loss may be higher in recipient mares carrying embryos from older donor mares.

Equiception has a pregnancy rate of 80% when transferring embryos to our own recipient mares. However, there is a significant variation of results associated with the time of season, with a noted decline in pregnancy rates in periods of high temperature.

The approximate costs of ET at Equiception B.V. (excluding 21% VAT) are the following: flush procedure: €267,50, excluding required drugs: approximately: €15,-, transfer procedure: €267,50, excluding required drugs: approximately €50,-, packaging and transportation of the embryo (to Equiception B.V. recipient mare site): €167,50 and lease of recipient mare: €2890,-.

For example, your donor mare is flushed twice as the first attempt does not result in an embryo recovery. The second embryo flush is successful; this embryo is transferred, resulting in a pregnant recipient. 2 x flush procedure and 1 x transfer procedure (including drugs) is €852,50. Total costs including packaging and transport of the embryo and the lease of the recipient mare add up to a total of €3.910,-

Depending on factors like the fertility of the donor mare and the semen and recipient mare factors, more or less flush and/or transfer attempts will be needed to result in a pregnant recipient. At Equiception B.V. the overall costs for a successfully pregnant recipient mare by ET are on average €4.700,-

Please refer to Equiception B.V. current pricelist (hyperlink) for all up to date costs.

One of the big advantages of embryo transfer is that mares in athletic competition can remain in performance and still produce offspring. However, disruption to training and competition schedules, for some mares at least, may be necessary to optimise embryo recovery rate as exercise, heat (including exercise-induced heat) and stress (including increased cortisol levels caused by transportation) can disrupt ovarian function. These factors should especially be considered in mares from which there is a repeated failure of embryo recovery in the absence of clinically detectable reproductive abnormality. To optimise embryo recovery, owners may have to accept that alterations to management will be necessary and potentially training as well as competition may have to cease entirely during the periovulatory period and the gap between insemination and flushing. Having said this, in many cases mares manage to conceive repeatedly and donate embryos despite the stresses of training, competition and transportation. This is very fortunate, nonetheless it is important for mare owners to have realistic expectations and realise caution is warranted when it comes to deciding to breed from competition mares.

ET is generally a safe and well-established assisted reproduction technique in mares with no detrimental effects on the mare’s future fertility.

Repeated cycles of breeding and embryo flushing, however, may predispose embryo donor mares to uterine inflammation and infection by the third to fifth cycle. These affected mares tend to accumulate fluid in their uterus, have inflammatory cells present on uterine cytology and show growth of bacterial organisms on uterine culture. Consequently, close attention is paid to the uterine health of individual donor mares and appropriate treatment initiated when needed.

Furthermore, rectal tears are a small, yet serious risk of every rectal palpation and can be life-threatening for the mare. Depending on the degree of the tear, conservative treatment or surgical management may be warranted. Overall prognosis for horses with rectal tears depends on size, grade and location of the tear, time between occurrence and treatment, and first aid measures applied.

All the veterinarians at Equiception B.V. are experienced and work with caution during rectal examinations and to increase safety, young inexperienced and fractious mares will be sedated just prior to the examination.