by Steve Connor
Science Correspondent
THE SCIENTIST who pioneered sheep cloning has admitted its commercial future may be doomed because many of the lambs are born abnormally large and die after birth.
The problem of the "giant" lambs keeps re-occurring, despite attempts to solve it since it was first identified last year.
Dr Ian Wilmut, leader of the cloning team at the Roslin Institute near Edinburgh, said last week that it now seriously jeopardises the exploitation of cloning technology.
"You do sometimes have an increase in size which is sufficiently great to threaten the wellbeing of both mother and offspring. Obviously you are not going to go on using a technique with those effects," Wilmut said.
The most recent cloning experiment produced lambs that were nearly twice the size born naturally. The cloning technique was almost certainly responsible, according to Wilmut.
Other research published earlier this year, which included work on Dolly, the first adult sheep clone, also produced oversized lambs. Dolly was, at 6.6kg, about a third heavier than she should have been at birth.
Scientists from the institute, which is government funded, and PPL Therapeutics, the private biotechnology company set up to exploit its research, last week announced the birth of the first cloned lambs that had been genetically altered to include human genes for a blood-clotting protein.
Of the six clones, one died within hours of birth while the others weighed between 3kg and 9kg. PPL maintained that their weights were within the normal range for the Poll Dorset sheep breed.
One of the lambs was delivered by caesarean section but PPL refused to give details of the individual birth weights, claiming this would prevent formal publication of the scientific research.
However, the Meat and Livestock Commission said that the typical birth weight of a Poll Dorset lamb is 4.75kg.
Jim Dufosee, spokesman for the Poll Dorset Sheep Breeders' Association, said he has never come across a lamb weighing more than 7kg at birth. "A 9kg lamb is impossible. You would never get it out," he said.
Animal welfare organisations criticised PPL for using the Scottish blackface, a small breed of sheep, as the surrogate mothers and a larger breed for the embryos.
Joyce D'Silva, director of Compassion in World Farming, said: "We believe this can cause great suffering to the animals in terms of painful births and caesarean operations. It should be banned."
Last year, when Wilmut vowed to address the problem of oversized lambs, he said: "If we still have this problem in the next generation of lambs, we will go back to the beginning."
Dr Alan Colman, the research director of PPL, said there is not yet enough information on the effects of transferring embryos from one sheep breed to another. "PPL will have to consider what data is available. If there are indications that lambs are bigger than they should be, one thing to look for is a larger breed to use as surrogates," he said.
He hailed the birth of the clones last week as "the realisation of our vision" to produce instant flocks of sheep that can be used for human therapeutic uses.
But Wilmut said: "Before this is used on a large-scale commercial project you would have to have eliminated the difficulties with large size and the increase in perinatal deaths."
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