LONDON (AP) - Dolly the sheep, the world's first mammal cloned from an adult, was euthanized well short of her normal lifespan after being diagnosed with progressive lung disease, her creators said Friday. The decision to end the life of 6-year-old Dolly was made after a veterinary examination confirmed the lung disease, a statement from the Roslin Institute said. Researchers had previously cloned sheep from fetal and embryonic cells, but until Dolly it was unknown whether an adult cell could reprogram itself to develop into a new being. The death of the famous clone was sure to raise the debate over whether animal cloneding from adults inevitably produces flawed copies. There are now hundreds of animal clones around the world, including cows, pigs, mice and goats, many of them appearing robust and healthy. But many attempts to clone animals have ended in failure. Deformed fetuses have died in the womb with oversized organs, while others were born dead. Still others died days after birth, some twice as large as they should have been. Dr. Harry Griffin of the institute said Friday that sheep can live to 11 or 12 years and lung infections are common in older sheep, particularly those like her which are kept indoors. ``A full post-mortem is being conducted and we will report any significant findings,'' Griffin said. Dolly was born July 5, 1996 in a research compound of the Scottish institute, and she created an international sensation when the achievement was announced on Feb. 23, 1997. Researchers had previously cloned sheep from fetal and embryonic cells, but until Dolly it was unknown whether an adult cell could reprogram itself to develop into a new being. The Dolly breakthrough heightened speculation that human cloning inevitably would become possible. Dolly, a Finn Dorset sheep named after the singer Dolly Parton, bred normally on two occasions with a Welsh mountain ram called David, first giving birth to Bonnie in April 1998 and then to three more lambs in 1999. In 1999, scientists noticed that the cells in Dolly's body - cloned from a 6-year-old sheep - had started to show signs of wear more typical of an older animal. Then in Jan. 2002, her creators announced she had developed arthritis at the relatively early age of 5 1/2 years, stirring debate over whether cloning procedures might be flawed. Some geneticists said the finding provided evidence that researchers could not manufacture copies of animals without the original genetic blueprint eventually wearing out. Dolly's body has been promised to the National Museum of Scotland and will eventually be put on display in Edinburgh, the Roslin Institute said.