Increasing Embryo Recovery Rates and Transfer Success

"With the continued changes in the equine industry, particularly the reproductive industry, we need to have a reasonable embryo recovery rate," said Jason J. Hudson, DVM, veterinary resident at Colorado State University (CSU). "With multiple foals able to be registered per year, along with superovulation in the mare and advances in cryopreservation of equine embryos, we need to have the ability to have enhanced embryo recovery rates."

Hudson found that embryo recovery can be enhanced by slight modifications of the standard embryo flush technique, and embryo transfer success can be improved by verifying that the embryo was not retained in the tip of the sheath with which the veterinarian performs the embryo transfer.

 In the commercial embryo transfer program at CSU, veterinarians attempted to recover 334 embryos in 2002-2004. A standard flush of three infusions using 4 liters of media yielded a 35% success rate in recovering embryos. After instituting an extra flush, 46 more embryos were recovered (14%). The overall recovery rate was 49% (163/334).

In a recent study performed at CSU where Hudson modified the flush technique (see the following description), 73 flushes were performed after 255 ovulations (these mares were superovulating due to equine follicle stimulating hormone provided by Bioniche). Hudson said 148 embryos were recovered (107 embryos were recovered after the standard flush and 41 were recovered after the "extra" flush), which worked out to a 58% embryo recovery rate. 

Hudson found:

  • There was an enhanced embryonic recovery rate if after the veterinarian added additional flushing media to the initial amount in the uterus, it was allowed to remain in the mare for three minutes, and the mare was given oxytocin (which helps contract the uterus and recover the fluid);
  • Age, fertility of donor mare, quality of the sire's semen, day of recovery, the number of ovulations, and the clinician's experience influence the embryo recovery rates;
  • The tip of the embryo transfer sheath should be rinsed with media post-transfer to ensure that the embryo hasn't been retained; and
  • Flushes of embryos on Day 6.5 (following ovulation) are much more difficult to retrieve than on Day 7 or early on Day 8.

The modified embryo recovery procedures were economically significant. The cost of the additional media, the oxytocin, and the clinician's time added up, but is minimal compared to the potential value of a recovered embryo. Hudson said it would be useful to find out if the additional flush, the three-minute waiting period, the oxytocin, or the combination of all three was the catalyst in improving recovery procedures.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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