U.S. Team Produces First Mule Clone

Stefan Lovgren
for National Geographic News
May 29, 2003
First there was Dolly, the sheep. Now, scientists at the University of Idaho have successfully cloned a mule. Born on May 4, Idaho Gem is the first member of the horse family to be cloned.

The successful cloning of a mule, and the groundbreaking research on which it was based, could have a significant impact on fields as diverse as cancer research and racehorse breeding, according to Gordon Woods, a professor of animal and veterinary science at the University of Idaho in Moscow, who led the research team.

It's also the first clone of a hybrid animal. A mule results from a cross between a female horse, or mare, and a male donkey, or jack. As hybrids, mules are almost always sterile.

The birth, the culmination of a five-year process, was unassisted and went off without a hitch. Only 12 minutes after being born, Idaho Gem stood up, and 33 hours later he was let out to play on the grass.

"He was shooting around like a rabbit," said Woods. "I think he's very cute, inquisitive and vibrant. He's quite an athlete."

Soon, Idaho Gem will even have company. Two more pregnancies, resulting from the same cloning procedure, are in the advanced stages with the next birth expected on June 9.


Cloning has occurred in nature for billions of years in plants and some animals. The term refers to the process of asexually producing an offspring that is genetically identical to a parent plant or animal.

In the laboratory, scientists use cell nuclear transfer techniques to produce animals with genetic material identical to just one parent. Scientists remove the nucleus from an egg cell, which contains the cell's genetic material, and replace it with genetic material from another somatic, or body tissue, cell.

An electric pulse fuses the egg cell and the new genetic material. The cell is then treated in an activation medium that allows it to develop into an embryo to be implanted in a surrogate mother's womb.

While in-vitro fertilization in cattle is routine, it is rare in horses. Despite numerous attempts, only two "test-tube" horses have been born, back in the late 1980s. The low cell activity in equine species makes both in-vitro fertilization and cloning more difficult in horses than in cattle and even humans.

Idaho Gem's DNA came from a fetal cell culture first established at the university in 1998. For three years, the team worked without success. After transferring the nuclei from the mule cells into 134 horse eggs and implanting them into mares, only two pregnancies resulted. Both failed.

But in 2001, the team began to focus on the calcium levels in the fluid surrounding the eggs. After they raised those levels, "the results were impressive and immediate," said Woods. The team established 14 pregnancies in 113 attempts. Eight of the pregnancies continued to at least the 40-day stage when heartbeats were detected.

Cancer Causes

The understanding of cellular biology in horses may offer new insights into cancer research.

The mortality rate for horses with metastatic cancer is eight percent for all cancers and zero percent for prostate cancer. By comparison, the mortality rate in humans is approximately 24 percent for all cancers, and 13 percent for prostate cancer.

"We believe there is a chemical explanation for this," said Woods. Calcium may be the key. Horses have a lower amount of intracellular calcium than humans and correspondingly a slower rate of cell activity. Their metabolism is slow compared to humans. Researchers believe the difference in cellular activity might play a role in cancer development and reproduction.

When Woods and his team increased calcium levels, putting them at a level closer to that of humans, they also increased the pregnancy success rate.

"Horses can be used as a key to understanding humans," said Woods. "It's important to understand what's regulating calcium activity. If there is a way to manipulate it, we could lower the risk of cancer in humans."

The Perfect Stallion

The discovery could also have a major impact on mule racing.

The main sponsor of the cloning project was Don Jacklin, an Idaho businessman with a passion for mule racing. The cloned foal is the full brother of Taz, Jacklin's best racer. Mule racing is gaining popularity in some parts of the country. But because mules are sterile, breeding new champions is difficult. Cloning is the only feasible way for a mule to reproduce.

Preliminary testing showed that the method developed by the researchers to successfully clone a mule should also work with a horse. But the Jockey Club, which regulates American thoroughbred racing, bans cloning.

Too bad, say some horsebreeders. They would love to clone Funny Cide, the remarkable thoroughbred that has collected wins at the Kentucky Derby and Preakness this year and could complete the Triple Crown with a win at the Belmont Stakes next month. Funny Cide is a gelding, a castrated male that is now a genetic dead end.

A summary of the research appears in the current issue of the journal Science.

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