Foals Born From Frozen Eggs for the First Time

Bijal P. Trivedi
for National Geographic Today

August 31, 2001

For more than two decades, horse breeders have been able to freeze the
sperm of prized stallions to sire healthy foals. Using similar methods
to preserve eggs harvested from mares, however, was not
successful—until now.

Last month, researchers at Colorado
State University (CSU) in Fort Collins celebrated the birth of Ethyl and
Vitreous, the first foals born from harvested eggs. The eggs had been
frozen for several months, thawed, and implanted into a surrogate
mother, which was then artificially inseminated.

"What is exciting for us is that we can now preserve the mares' genetics forever," said Ed Squires, director of the Equine Reproductive Laboratory at CSU.

Freezing the eggs of mares has been difficult because of the relatively large size of the eggs. They are the largest cell in the horse's body and contain a lot of water. If frozen too quickly, they tend to explode.

The researchers made a breakthrough by developing a technique to reduce the amount of water in a mare's eggs by pre-treating them with a clear syrupy liquid called ethylene glycol—from which the new foal Ethyl got her name. This protects the cells from being destroyed as they're frozen.

Then the eggs are dipped into liquid nitrogen, which quickly freezes them at a chilly minus 186 degrees Celsius (minus 302 degrees Fahrenheit). The freezing process is called vitrification, for which Vitreous was named.

"Ethylene glycol helps the cell go from a liquid to a glass-like state without exploding," said Lisa Maclellan, who participated in the project at CSU.

Winning Traits

Harvesting and freezing the eggs of a mare is desirable for a number of reasons.

"Some mares are too busy competing or performing and simply don't have time to produce a foal," said Maclellan. In such cases, the only way to pass on the winning traits of these "career" mares may be to harvest their eggs and implant them into other mares that will give birth to the foals.

If a prized mare dies unexpectedly, the eggs from her ovaries can be harvested quickly and stored. When a suitable mate is found—even decades later—the eggs can be implanted in a surrogate mother to continue the dead mare's genetic line.

Before the technique developed by Squires's team can be commercialized, it must be improved.

"Right now we have about a 15 percent success rate," said Maclellan. "We had two successful pregnancies out of about twelve."

Squires believes the procedure would need to have a success rate of 50 to 75 percent before it could be commercialized.

Growing Market Demand

Changes in the horse-breeding industry suggest there may be a huge market for frozen eggs as well as sperm.

New rules now allow frozen sperm to be used for breeding American Quarter Horses and American Paint Horses, which are the largest breeds in the United States. Together they produce more than 200,000 foals each year, said Squires.

Although the first foal produced from frozen sperm was born in 1957, the use of frozen sperm for breeding was not accepted until recently because there were no tests that could verify the parentage.

"Now, with DNA fingerprinting and other genetic techniques, we are able to confirm parentage," said Squires.

"Within the next five to ten years, freezing techniques will revolutionize breeding, allowing us to move valuable genetic material from horses around the world like never before," he added.

The researchers hope the freezing procedure also may prove effective for harvesting the eggs of endangered species.

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