The unassisted birth was "a further demonstration" that the cloning method used to produce Dolly has not hampered her ability to breed normally and produce healthy offspring, said Dr Harry Griffin, assistant director of the Roslin Institute near Edinburgh, where the sheep lives.
It could have important implications if human cloning were ever made legal. The cloning method, by which the nucleus of an egg cell is replaced by that of an adult cell, appears to "reset the clock" of the cell, which means that clones can breed normally. If that did not happen, Dolly would behave like a nine-year-old sheep, rather than a three-year-old, because the cells used to create her came from the udder of a six-year-old ewe. She was born in July 1996.
Similarly, a human cloned from a 50-year-old would apparently start at the same age as any other baby, though scientists are still unsure whether accumulated damage to the "parental" DNA would affect the clone late in life.
Dolly, the first mammal to be successfully cloned from an adult cell, was already a mother: she gave birth to Bonnie last spring. The newborn lambs are being kept in a special pen at one of the institute's farms, where there is infra-red heating. They have the same father as Bonnie - a Welsh mountain ram called David. "Dolly and her lambs [two males and one female] are in good health. The births were unassisted and all three are suckling well," the institute said.
Dr Griffin added: "We are delighted. The birth of Bonnie almost exactly 12 months ago confirmed that despite Dolly's unusual origins, she is able to produce healthy offspring. It's a nice story at Easter - a pleasant one, when there's a lot less pleasant news around."