It is the first detailed study of the physiology of a cloned animal from birth and the scientists say the results "should be taken into account in debates on reproductive cloning in human beings."

Dr Harry Griffin: There are clearly problems which need to be overcome

Dr Harry Griffin, at the Roslin Institute, Edinburgh, where Dolly was created, told BBC News Online: "This reinforces the point we have made repeatedly in response to speculation about human cloning.

"No-one should be contemplating the cloning of a human being using technology which is at a very early stage of development and the mechanisms of which we understand very little."

Red blood cell counts

The research was carried out at the Institute National de la Recherche Agronomique, France, by Dr Jean-Paul Renard and his colleagues.

They took an ear cell from a healthy adult cow and used it to create a new clone. The adult cow was itself a clone, but was made using an embryonic cell. Six weeks after the calf was born, there was a sudden, dramatic fall in its red blood cell counts.

It died a week later. It had also lost many lymphocytes, a white blood cell important for the immune system. A post-mortem showed that the lymphoid tissues - spleen, thymus and lymph nodes - had not developed normally.

The scientists considered two possible causes. In the first, they examined the idea that there was something wrong with the process of embryo transplantation. This is necessary because all clones are born from surrogate mothers.

The second possibility centred on the use of adult cells in the new technique of cloning. This requires genetic material taken from these cells to be "re-set" so that the complete instructions contained in the DNA to be acted upon.

Problems to overcome

The scientists reasoned that because the adult cow had undergone implantation and was perfectly healthy then it must be the use of adult cells that was the likely cause of the calf's deformity and death.

"Nuclear transfer involves the reprogramming of adult, differentiated cells and persuading them to act like early-embryo cells," said Dr Griffin. "It's not surprising at all that it doesn't work all the time."

Dr Griffin points out that this study involved only one animal and cannot be used to make broad conclusions. But he said that this type of research must be done more often in the future.