Embryo Transfer
Article by Caro Dach, an equine management student from Germany.
To find more such articles and join the network of equine students worldwide go to www.equineinvestigator.com

Can you spot the link between the pictures?

Picture 1 shows the famous show-jumping mare Weihaiwej with Franke Sloothak who won individual and team gold at the World Championships in 1994. And you probably have already noticed the similarity between her and the fillies shown on Picture 2 and 3. Indeed, both are foals of Weihaiwej, the one on Picture 2 was born in 2001 at Couvains’ stud in France. But Weihaiwej never carried a foal to term herself. So, how did that work then …?

All foals were obtained via embryo transfer by artificially inseminating Weihaiwej, removing a fertilized egg from her and transferring it into a recipient mare. Until now, Weihaiwej had seven foals via embryo transfer which are all owned by San Patrignano in Italy; the last one is shown in Picture 3.

In 2000, Vanderwall reported that embryo transfer is nowadays the most common assisted reproductive method for mares and allows also less fertile or reproductively unsound mares and mares with non-reproductive health problems to have offspring. Hopkins and Meadows (2003) stated that one of the most obvious advantages for ET is an increase in the annual reproductive rate from mares because multiple foals can be obtained in one year (preferable for sport horses). Furthermore, young two year old mares are now already able to have offspring which is worthwhile for breeders who have young, valuable mares and can obtain foals from them earlier.

The first embryo transfer was reported in the 1970s, but embryo transfer was not largely accepted by the equine breeding industry until the 1980s (Vanderwall 2000).

In 1987, Sirois et al. carried out an experimental application in an Equestrian Teaching Center with the goal to produce as many foals as possible from selected mares in one breeding season. The study included only five donor mares and embryo collection was done at 25 occasions 6.5 days after ovulation. 17 embryos were collected, 13 were transferred directly, 3 were frozen and one was lost. From the 13 transferred embryos, 8 started to develop, but only 5 led to foals (38 %). To sum up, five donor mares have produced five foals while having been out of competition or teaching for three months.

The application showed that embryo transfer can be used in a short time-interval to produce multiple foals from mares which otherwise have to interrupt their normal use of purpose for a longer period of time. Even though the study indicated that the loss of embryos is quite high (9 from 17); it should be borne in mind that the technology has considered improved since that date.

Before commencing embryo transfer, a soundness examination of the donor mare is recommended ensuring that she is in optimal bodily condition without any health problems and has normal heat cycles (Vanderwall 2000; Hopkins & Meadows 2003). Actual breeding management of the donor mare contains teasing to monitor reproductive behaviour, and palpation and ultrasound to look at the ovarian follicular activity during estrous (Vanderwall 2000). Hopkins & Meadows (2003) recommend mares which are between 3 to 10 years old and sound. Vanderwall (2000) explains further that synchronization of estrous can be accomplished trough hormones like prostaglandin for instance. It is achieved if the recipient mare ovulates 1 day before to 3 days after the donor mare. In his view the optimal date for an embryo collection is therefore day 7 or 8 after ovulation.

Embryo collection takes place non-surgically by using transcervical uterine lavage. According to Hopkins and Meadows (2003), the uterus is flushed with a fluid which is afterwards examined for embryos and normally, in 50 % to 80 %, 1 or 2 embryos are found. The transfer of the embryo usually takes place at room temperature within 1 hour after collection. The transfer can either be applied surgically or non-surgically, whereas the non-surgical transfer is more common (Vanderwall 2000). Hopkins & Meadows (2003) state pregnancy rates in recipient mares inseminated non-surgically ranging from 40 % to 70 %.

Ed Squires (1999) which could be named as a pioneer in developing embryo transfer techniques in horses talked about a huge development in 1999 when it was possible to store embryos at 5 degrees Celsius. Thus, they stayed viable for at least 24 hours and it was possible to transport them to a specialized station for embryo transfer into recipient mares (Vanderwall 2000).

In 2007, this technology seems to be a little out-of-date when Smith Thomas reports that embryos can now be vitrified making them retainable for months with a success rate from

60 % to 70 %. In view of the international focus of the equine breeding industry this is an important and pioneering possibility.

Nevertheless, the use of embryo transfer in horses cannot be compared to the use of ET in other species like cattle (Sirois et al. 1987). Superovulation (production of multiple follicles), widely used in other species, remains difficult in the horse (Squires 2001). Pregnant Mare Serum Gonadotrophin (PMSG) and Follicle Stimulating Hormone (FSH) are used for superovulation in other species (Bowen et al. 1985). In a study undertaken for Colorado State University, Squires et al. (1999) investigate whether FSH extracted from sheep or pigs increases multiple ovulations in horses. Results showed that at this point in time the technique seemed to be relatively ineffective.

Smith Thomas (2007) reports for the US Horse Magazine that since 2004, eFSH (equine Follicle Stimulating Hormone) produced by Bioniche (Canadian biopharmaceutical company) is on the market and should make superovulation in horses feasible. The Colorado State University played an important role in advocating research on eFSH and obtained generally good results for its use. Another study presented to the American Association of Equine Practitioners showed that eFSH increased follicular development, but the number of ovulations per cycle were not significantly higher than without hormonal treatment (2.3 versus 1.5). On the other hand, the difference in embryo recovery was remarkable (1.3 embryos per cycle versus 0.5 in untreated cycles). Further studies are needed to confirm the effectiveness of eFSH.

Embryo transfer is an advanced reproductive technology, but despite all advantages, disadvantages arose, mainly caused by the breeding associations which have no standardized rules for applying embryo transfer. Hopkins & Meadows (2003) indicate that limitations to register offspring obtained by embryo transfer are common at the breeding associations. According to Ed Squires (2001), the horse industry is not utilising embryo transfer to its full potential due to their restrictions regarding the registration of the embryo transfer offspring. To date, embryo transfer remains a very expensive way to produce offspring (Hopkins & Meadows 2003). Smith Thomas (2007) mentions costs which vary from $ 2.000 to $ 5.000, but normally include a recipient mare which has to be returned later on.

Looking to the USA, the number of equine embryo transfers has been increased in 2002 and 2003, according to first changes which were made from the breeding associations regarding the registration of foals obtained through embryo transfer (Hudson & McCue 2004). Quarter Horse, Paint, Arabian, Appaloosa and Peruvian Paso breed registries, as well as several draft and warmblood breeds allow embryo transfer in the USA (Smith Thomas 2007).

Although still expensive today, embryo transfer is extremely useful for more valuable mares to make sure their genetic potential is passed on. Further research is necessary in order to increase the success rate with embryo transfer which is economically needed. Most importantly, breeding registries will have to clarify regulations regarding the registration of embryo transfer offspring, in order to ensure that embryo transfer lives up to its full potential.

This article was written by Caro Dach, an equine management student from Germany.

To find more such articles and join the network of equine students worldwide go to www.equineinvestigator.com

References

AAEP Convention 2006: Reproduction, ‘Superovulation and Embryo Transfer’, Retrieved from The Horse magazine (www.thehorse.com), Article # 9184, March 01 2007

Bowen, MJ, Salsbury, JM, Bowen, JM, Kramer, DC 1985, ‘Non-surgical embryo auto-transfer in the mare’, Equine Vet J 3 (Suppl): 100-02

Hopkins, FM, Meadows, DG 2003, ‘Embryo Transfer in Mares’, The University of Tennessee, TNH-1003 2/03, Retrieved from Agricultural Extension Service (www.utextension.utk.edu)

Hudson, JJ, McCue, P 2004, ‘How to Increase Embryo Recovery Rates and Transfer Success’, 50th Annual Convention of the American Association of Equine Practitioners, 2004 - Denver, CO, USA, (Ed.). Publisher: American Association of Equine Practitioners, Lexington KY., Retrieved from International Veterinary Information Service (www.ivis.org), Last updated: 4-Dec-2004; P1473.1204

Sirois, J, Betteridge, KJ, Brault, A 1987, ‘Transcervical Embryo Transfer in Horses: An Application in an Equestrian Teaching Center’, Can Vet J Volume 28, No. 12 December 1987

Smith Thomas, H 2007, ‘Embryo Transfer: Who’s Your Mama?’, Retrieved from The Horse magazine (www.thehorse.com), Article # 8822, February 01 2007

Squires, E, McCue, PM, Vanderwall, DK 1999, ‘The current status of equine embryo transfer’, Recent Advances in Equine Theriogenology, Issue 01/99, 51(1):91-104

Squires, E 2001, ‘Artificial Reproductive Technologies – Is the Horse Industry Ready? – Interview with Ed Squires, Retrieved from Australian Government Equine Research and Development Program (http://www.usyd.edu.au/su/rirdc/articles/index.htm), Issue 03/01

Vanderwall, DK 2000, ‘Current Equine Embryo Transfer Techniques’, Retrieved from International Veterinary Information Service (www.ivis.org), Document No. A0204.0400

Graphic 1, Retrieved from http://www.horsetalk.co.nz/archives/2006/0608/p/058.jpg, On June 4th, 2007

Graphic 2, Retrieved from http://www.semilly.com/images/weihaiwej.jpg, On June 4th, 2007

Graphic 3, Retrieved from http://cavalliecani.sanpatrignano.org/page.php?sid=1809, On June 4th, 2007