Oocyte Transport Protocols and Success Rates

Oocyte Transport Protocols and Success Rates

Intracytoplasmic sperm injection (ICSI) is a form of fertilization in which a single sperm is injected directly into an egg.

Photo: Courtesy University of Idaho

The practice of shipping stallions' semen across the country, and even around the world, is a mainstay in today's equine reproduction industry. Collecting and transporting mares’ oocytes (egg cells) in a similar fashion, then fertilizing and implanting them into donor mares could save breeders money—and donor mares from having to take long, expensive, and potentially health-compromising trailer rides. Veterinarians are determining whether this technique could be a viable approach for saving time and money.

Intracytoplasmic sperm injection (ICSI) is a form of in vitro fertilization in which a single sperm is injected directly into an egg. The technique is not commonly used in equine medicine, but Rob Foss, DVM, of Equine Medical Services, Inc., in Colombia Mo., said, “Its use is increasing for mares that are unable to produce embryos any other way and also for stallions whose available sperm numbers are low.” But, because only a handful of facilities offer the procedure, horse owners often have to transport their mares great distances at great cost, racking up hefty price tags even before procedures get under way.

At the 2013 American Association of Equine Practitioners’ Convention, held Dec. 7-11 in Nashville, Tenn., Foss described a study he and colleagues performed to determine the effect of shipping oocytes on the eventual fertilization rate.

The team incubated two types of oocytes—those recovered from dominant (mature) follicles after inducing ovulation via deslorelin administration (and those from subordinate (immature) follicles—overnight in various media and at varying temperatures to mimic the effects of transport. Then the team performed ICSI using the incubated oocytes and compared the groups’ blastocyst (early embryo) production rates.

All oocyte groups produced blastocysts, but the rate of production varied among follicle types and conditions. Oocytes from dominant follicles produced better blastocyst rates, but they were more sensitive to temperature changes and simulated shipment delays. On the other hand, oocytes from immature follicles could be shipped in a commercially available medium since they were less sensitive to a chemical environment, as well as the variables of temperature and time, tha mature follicles are.

Foss reported that the most successful protocols in the study achieved blastocyst production rates that are similar to those reached when performing ICSI on-site.

He noted that the oocyte donor mares used in this study were all 12 years of age or younger; the typical clinical ICSI donors are in their late teens to early and mid-20s, which could affect the study's applicability to real-life donors. Foss said that older mares’ blastocyst rates are lower than those of younger mares; production rates among an older population of mares might not be as high.

From a practical standpoint, Foss said more work needs to be done to determine what conditions are best for shipping oocytes. He cautioned that while these methods are producing pregnancies and foals, more work is needed to compare the viability of pregnancies resulting from shipped oocytes to those produced from transfer performed on-site.

About the Author

Christy Corp-Minamiji, DVM

Christy Corp-Minamiji, DVM, practices large animal medicine in Northern California, with particular interests in equine wound management and geriatric equine care. She and her husband have three children, and she writes fiction and creative nonfiction in her spare time.

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