Pregnancies from Dead Mare Ovaries

"You think breeding mares on foal heat is tough, try dead mares!" said Elaine Carnevale, DVM, PhD, professor in equine reproduction in the department of biomedical sciences at Colorado State University (CSU), with a laugh as she began her talk following a presentation on foal heat breeding success. Her presentation at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004, covered CSU's work with deceased mares' ovaries and oocytes, and their success rates.

"Death or euthanasia of a valuable mare results in loss of her genetic potential," she said. "However, when a mare dies, her ovaries still contain potentially viable oocytes that can be harvested to produce additional offspring. Some mares seem to have a lot of viable oocytes, while others have very few."

Factors that can affect this are:

  • Donor variability;
  • Age and fertility;
  • Time of year (seasonal variations in ovarian activity);
  • Quality of oocytes;
  • Medical history and treatment;
  • The interval from death to harvest and use; and
  • The transportation interval and conditions.

"This technique also has clinical use," Carnevale added. "In 2001, a Quarter Horse mare was euthanized, and her ovaries were transported to CSU. We transferred five oocytes, had five embryonic vesicles in a recipient's uterus, and got a healthy foal."

She further reported that in this retrospective study, this technique had been used with ovaries from 27 mares that were four to 30 years old. The ovaries are very sensitive, so they need to be kept isolated and padded during transport, she said. Two mares that were more than 20 years old yielded zero viable oocytes or one of poor quality, so no oocytes were transferred from them. From the remaining 25 mares, a total of 226 oocytes were harvested. Oocyte transfer was done with 191 (72%) of the oocytes; one to three recipients per donor (a total of 46 recipients) had one to 14 donated oocytes placed in their oviducts.

"Thirty percent (14/46) of recipients were diagnosed as pregnant with one or more embryonic vesicles by Day 16," she reported. "Six of the 14 pregnancies (43%) were lost by Day 60. To date, no pregnancy losses have occurred after Day 60. Currently, seven foals have been born."

She noted that their work had shown an embryo loss rate of 43% for these mares. "Many (donor) mares were older, sick, and/or ovaries had been exposed to very low temperatures," she said. Also, ovarian activity at the time of death varied greatly. But the researchers had foals or ongoing pregnancies for 24% of donors.

"All of the foals have been normal and healthy," she said. "Most problems end up in embryo loss; once they get on the ground, they're pretty normal."

She described in detail the procedures for removing and transporting the ovaries, as well as harvesting the eggs and working with the recipients. She noted that with a transport interval of less than one hour (between ovary harvesting and oocyte recovery work beginning at CSU), they found a pregnancy rate of 36% per oocyte recovered. However, if the transport time lengthened to eight to 26 hours, the pregnancy rate per oocyte dropped to 10%. She described the optimal temperature for long transport intervals as 12-22 degrees Celsius (53.6 to 71.6 degrees Fahrenheit).

She concluded that roughly one of four donors had yielded pregnancies, and commented that "For younger mares, such as those dying from traumatic injury, for which transportation time was short, I think (pregnancy) rates will be quite good."

Future considerations for donor selection might include age, ovarian activity, and medical treatment, she said. Future considerations for offering the service might include increased locations to minimize transport distance and time.

One attendee asked if euthanasia solution might be problematic for the work. "Possibly, we just don't really know yet," answered Carnevale. "We don't yet know if that's actually decreasing our pregnancy rate.

"When faced with the death of a valuable mare, owners can be given the option to attempt to obtain additional pregnancies," Carnevale concluded. "If possible, euthanasia should be planned to minimize the transportation interval and the time that the ovaries remain in the mare after death. A semen shipment must be arranged, and hair follicles should be collected if needed for DNA analysis for the respective breed registry."

More Options

She also mentioned cryopreservation of oocytes for getting foals from subfertile mares. While this has resulted in two normal, healthy foals, Carnevale noted that the problem with this technique is, "the efficiency of the procedure is so low it probably won't help us with these already compromised oocytes."

Intracytoplasmic sperm injection (ICSI) is another option in which sperm is injected directly into the egg. "It reduces the amount of semen required, reduces potential cost, and might increase efficiency. It's potentially a very good way to go," she commented.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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