The current status of equine embryo transfer.
Abstract: The use of embryo transfer in the horse has increased steadily over the past two decades. However, several unique biological features as well as technical problems have limited its widespread use in the horse as compared with that in the cattle industry. Factors that affect embryo recovery include the day of recovery, number of ovulations, age of the donor and the quality of sire's semen. Generally, embryo recoveries are performed 7 or 8 d after ovulation unless the embryos are to be frozen, in which case recovery is performed 6 d after ovulation. Most embryos are recovered from single-ovulating mares. Because there is no commercially available hormonal preparation for inducing multiple ovulation in the horse, equine pituitary extract has been used to increase the number of ovulations in treated mares, but FSH of ovine or porcine origin is relatively ineffective in inducing multiple ovulation in the mare. Factors shown to affect pregnancy rates after embryo transfer include method of transfer, synchrony of the donor and recipient, embryo quality, and management of the recipient. One of the major improvements in equine embryo transfer over the last several years is the ability to store embryos at 5 degrees C and thus ship them to a centralized station for transfer into recipient mares. Embryos are collected by practitioners on the farm, cooled to 5 degrees C in a passive cooling unit and shipped to an embryo transfer station without a major decrease in fertility. However, progress in developing techniques for freezing equine embryos has been slow. Currently, only small, Day-6 equine embryos can be frozen with reasonable success. Additional studies are needed to refine the techniques for freezing embryos collected from mares 7 or 8 d after ovulation. Demand for the development of assisted reproductive techniques in the horse has increased dramatically. Collection of equine oocytes by transvaginal, ultrasound-guided puncture and the transfer of these oocytes into recipients is now being used to produce pregnancies from donors that had previously been unable to provide embryos. In vitro fertilization, however, has been essentially unsuccessful in the horse. One alternative to in vitro fertilization that has shown promise is intracytoplasmic sperm injection. However, culture conditions for in vitro-produced embryos appear to be inadequate. The continued demand for assisted reproductive technology will likely result in the further development of techniques that are suitable for use in the horse.
Publication Date: 2000-03-23 PubMed ID: 10729065DOI: 10.1016/s0093-691x(98)00234-9Google Scholar: Lookup
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Summary
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The research paper discusses the current state of equine embryo transfer, detailing factors which affect recovery and pregnancy rates, and highlighting improvements and challenges faced in the practice. It also highlights alternative reproductive techniques being explored.
Equine Embryo Transfer: Overview and Limitations
- The research starts by pointing out that despite its growing mainstream acceptance, equine embryo transfer’s use is not as widespread as in the cattle industry. Biologically unique features, technical issues, and variables like the timing of recovery, number of ovulations, age of donor, and semen quality are cited as reasons.
- Embryos get recovered usually after 7 or 8 days following ovulation, except in cases of intended freezing wherein it’s done on the 6th day. The majority of these embryos are collected from single-ovulating mares.
- Due to the absence of commercial hormonal treatment for inducing multiple ovulation in horses, equine pituitary extract is often used. However, FSH derived from sheep or pigs has shown comparatively little effectiveness in causing multiple ovulation in the mare.
Pregnancy Rates Post-Embryo Transfer
- Aspects influencing pregnancy success post-embryo transfer include the transfer method employed, the donors and recipients’ synchrony, embryo quality, and recipient management.
- One of the key advancements discussed is the capacity to store embryos at 5°C, enabling their transportation to a central location for grafting onto recipient mares. This process involves practitioners collecting the embryos on the farm, chilling them to 5°C in a passive cooling unit, and sending them to an embryo transfer station, with minimal impact on fertility.
- It was noted, however, that progress on strategies for freezing equine embryos has been sluggish. So far, only smaller Day-6 equine embryos have been successfully frozen to reasonable degrees of success.
Assisted Reproductive Techniques
- The paper ends with a look at the increased demand for alternative reproductive technologies. For instance, the collection of equine eggs by transvaginal ultrasound-led puncture and the transfer of these eggs into recipients is now used to induce pregnancy in donors previously unable to produce embryos.
- In vitro fertilization has not met with success in horses. However, a viable alternative, intracytoplasmic sperm injection, shows promise.
- The research concludes that due to the rising demand for assisted reproductive technology, there will likely be further developments of suitable techniques for horse reproduction
Cite This Article
APA
Squires EL, McCue PM, Vanderwall D.
(2000).
The current status of equine embryo transfer.
Theriogenology, 51(1), 91-104.
https://doi.org/10.1016/s0093-691x(98)00234-9 Publication
Researcher Affiliations
- Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins 80523, USA.
MeSH Terms
- Animals
- Embryo Transfer / trends
- Embryo Transfer / veterinary
- Female
- Horses / embryology
- Male
- Pregnancy
References
This article includes 58 references
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