Starting with Dolly the sheep, scientists have successfully duplicated pigs, cows, cats, rabbits and rodents. The cloning of horses and other equids eluded them, however, despite numerous attempts. In the new work, Gordon Woods of the University of Idaho at Moscow and his colleagues fused DNA from fetal mule cells with enucleated horse eggs and coaxed the manipulated eggs into maturing by boosting the calcium levels in the cultures. (Previous studies hinted that low calcium concentrations in the cell environment were thwarting development.) The team then implanted 305 of these oocytes into surrogate mares. At the time of Idaho Gem's birth, two other mares were still carrying cloned mule fetuses.
Thus far Idaho Gem--the sibling of a champion racing mule named Taz--appears to be developing normally, Woods and his collaborators report. Meanwhile, a cloned horse may not be far off. An Italian team and an American team have mares expected to give birth in coming months.