Scientists seem to think that they can mix and match animals' genes in a controlled way, but actually the control is an illusion

Sarah Kite, BUAV

Professor Ian Wilmut, of the Roslin Institute in Edinburgh, which produced Dolly, has called for a research programme to establish the impact cloning has on animal health. But animal welfare groups have called on scientists to halt their experiments.

They say the revelation proves cloning is harmful to animals and has raised fresh doubts about cloning animals for use in human transplants.

'Innocent animals'

Sarah Kite, research and information director at the British Union for the Abolition of Vivisection (BUAV) said: "Scientists seem to think that they can mix and match animals' genes in a controlled way, but actually the control is an illusion.

"No-one yet understands exactly how genes work or what the effects will be on the innocent animals who are subjected to biotechnology."

The Dolly technology has been used to produce pig clones

The animal welfare group Compassion in World Farming has also called for a halt to cloning.

Its director, Joyce D'Silva, told BBC Radio 5 Live: "I think of the hundreds and hundreds of other cloned lambs who have been born and had malformed hearts, lungs or kidneys.

"They have struggled to survive for a few days and then had their lungs filled with fluid and gasped their way to death or had to be put our of their misery by their creators.

"That is the real story of cloning."

Share results

Professor Wilmut revealed on BBC Radio 4's Today programme that Dolly, the first mammal clone made from an adult cell, had developed arthritis in her left hind leg.

He said: "There is no way of knowing if this is down to cloning or whether it is a coincidence. We will never know the answer to that question."

Professor Wilmut: Cloning has great potential

He said that there needed to be a systematic assessment of the health of animal clones. And he accepted that scientists might be too commercially motivated.

However, he continued: "This is a very young technique.

"It has great potential. As well as studying the animals that are there already, we have to continue with the process to improve and use the technology."

It is unusual but not unknown for a relatively young sheep to develop arthritis.

This has raised the question of whether the cloning process led to Dolly's problem and whether cloning always gives rise to unhealthy animals.

Many cloning companies have reported that their animals are healthy. But there has been no independent assessment of the long-term health of animal clones.

And there is plenty of anecdotal evidence of animals being born overweight, malformed and with damaged immune systems.

Pig cloning race

The news came as rival teams announced the birth of genetically engineered pig clones that might be suitable for animal-to-human organ transplants.

One litter of pigs was born on Christmas Day at the US research division of PPL Therapeutics Plc, a commercial offshoot of the Roslin Institute.

Another team, a joint venture between Novartis AG and BioTransplant Inc, revealed that similar pig clones had been born several months before.

The move towards breeding animals for organs has been condemned by animal rights campaigners. But others argue that the research could lead to a supply of organs to help patients on the transplant list.