Tornado Story Twists Again: Colorado State Artificially Inseminates Dead Mare’s Eggs, Fetuses Thriving via Surrogate Mares

When a devastating tornado hit Windsor, Colorado, around noon on an otherwise quiet day in May, a 12-year-old mare named Tuesday had to be euthanized. Tuesday’s owner, Jennifer Mears, is looking forward to not one but two foals who will be born about 11 months after Tuesday’s death. The clincher: Tuesday will be their mother, yet she was not pregnant when she was killed.

Colorado State University veterinarians were able to harvest Tuesday’s ovaries after she was euthanized from critical injuries she suffered after the tornado rolled a shed on top of her, shattering part of her leg. Soon after, staff at the university’s world-renowned Equine Reproduction Laboratory collected eggs from the ovaries and fertilized the eggs using advanced sperm injection techniques.

The fertilized eggs, called embryos, were implanted into surrogate mother mares. Mears just recently got the news that two of the four surrogate mares will foal this spring if all continues to go well during their pregnancies.

Both foals are somewhat of a miracle, said Dr. Pat McCue, director of the Equine Reproduction Laboratory. Working quickly, doctors in the hospital harvested 20 eggs from Tuesday the evening she died. Of those eggs, eight developed into embryos after being inseminated at the ERL, and the best four were implanted into four separate mares.

“There was a 30 percent chance that just one embryo would take, and it was something of a miracle that two pregnancies survived in surrogate mares,” said McCue, who performed the work pro-bono after volunteering in Windsor with his family after the storm and getting an eyewitness account of the devastation. McCue cautions that, like all pregnancies, something may still go amiss before the two mares carry their foals to full term. However, he remains optimistic – both of the surrogate mares are healthy and doing well. “Both mares have very normal-looking pregnancies, and we have healthy heartbeats in each of the two embryos.”

The ERL specializes in assisted reproduction of horses, with experts who see mares and stallions from around the world and work to develop new technology to preserve their bloodlines. In addition, much of the innovative work at the ERL also benefits humans. Several techniques used today in reproduction assistance were pioneered at the ERL including semen freezing and cooling. The center also was the first to harvest eggs from deceased mares and develop full-term, healthy foals.

“This is a way to continue the reproductive life span of great horses that by themselves are no longer able to get pregnant or carry a foal to term,” McCue said.

When unexpected losses of a mare or stallion occur, teams coordinated by Dr. Elaine Carnevale and Jason Bruemmer have been instrumental in salvaging eggs and sperm to preserve bloodlines. The teams make it possible for new foals to be born from deceased parents at least once a month, and have assisted with dozens of such pregnancies over the last few years as the technology has advanced.

Mears, her sister Mandy and her mother Wendy have followed the progress of Tuesday’s future foals from the emergency room harvesting of the ovaries, to the intricate process of fertilization when a sperm was is injected into the egg with a tiny glass needle, to watching the splitting of the initial cells into an embryo in the laboratory, to the moment when Dr. McCue discovered the pregnancies during follow-up ultrasounds. And finally, the thrill of the ultrasound examination and hearing the sound of two new hearts beating.

One of the pregnant surrogate mares, Katie, is owned by the Mears family. The other pregnant surrogate mare is owned by the ERL and was renamed Friday by McCue as a tribute to Tuesday. Mears already has names picked out for the foals who will carry on Tuesday’s life: Wednesday and Thursday.




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