British scientists say the world's first cloned mammal, Dolly the sheep, has developed arthritis. The announcement raises new questions about the practice of cloning animals, as we hear from correspondent Michael Drudge in London.

Scientists say Dolly the sheep has developed arthritis in the hip and knee of her left leg.

She has come down with the ailment at the age of five-and-a-half, years earlier than most sheep, who typically have a life expectancy of 13 years.

Ian Wilmut is the leader of a team that cloned Dolly in Scotland in 1996. He told British radio Friday that Dolly may be aging prematurely.

"The fact that Dolly has arthritis at this comparatively young age suggests that there may be problems. We don't know, and it is very important that we look," he said.

Mr. Wilmut says that in other aspects, Dolly is leading a normal life, and she has given birth to six healthy lambs.

Still, Mr. Wilmut points out that most attempts to clone animals have ended with deformities and early death.

He is calling for a systematic, large-scale study of cloned animals, and he appealed for companies that are raising cloned animals to share their observations.

Animal rights groups say Dolly's arthritis proves cloning is dangerous. Dan Lyons is an activist for an animal protection society called CAGE.

"You cannot just interfere with one aspect of an animal's system and expect the rest of the system to continue to function perfectly. This is just the latest report of animal welfare and health problems with cloning," he said.

Mr. Lyons has warned that commercial pressure on companies developing cloned animals is overriding the need for scientific caution.