Scientists have developed a new method of creating genetically-modified animals that addresses one of the principal objections of the anti-GM movement.
The "gene-editing" technique is at least 10 times more efficient than existing GM technology and crucially does not involve the use of antibiotic-resistance genes, which has been heavily criticised by opponents.
Researchers at the Roslin Institute in Edinburgh, where Dolly the cloned sheep was created in 1996, announced today that they have created the first GM pig with the technique as part of an ambitious project to produce disease-resistant animals by genetic engineering.
The male piglet, designated "pig 26" and born last August, has been genetically engineered with the smallest of DNA mutations - a single deletion of one out of the 3 billion chemical "letters" of its entire genome.
Scientists said that the power of the new gene-editing technique is that it is extremely precise and improves the efficiency of creating GM animals by ten-fold or more.
It can be performed on fertilised eggs rather than ordinary tissue cells and does not need the antibiotic resistance "markers" and the elaborate cloning process that previous techniques relied on to produce GM animals.
Professor Bruce Whitelaw of the Roslin said that the new technique produces GM animals with between 10 and 15 per cent efficiency compared with an efficiency of less than 1 per cent for the standard method of genetic engineering.
"We can do it without any marker or trace. Unless you do an audit trail there is no way that you would know how that mutation happened. It could have happened naturally, or by a DNA editor," Professor Whitelaw said.
In effect, because the new gene-editing technique does not leave any mark in the animal's genome other than the desired mutation, it merely mimics the natural evolutionary process but using a man-made genome editor.
"With the new technology we can work directly within the zygote [fertilised egg] with an efficiency of 10 to 15 per cent. In a litter of pigs at least one of the animals will have the edited event," Professor Whitelaw said.
"We can get rid of antibiotic resistance and for some situations we can get rid of cloning or nuclear-transfer technology as well. I think cloning does have some baggage attached to it," he said
"We as scientists are very excited about this because of very precise changes, and we see this as very powerful, but whether the public will see that as inherently different is another matter altogether," he added.
Pig 26 is part of a research programme to create GM pigs that are resistant to infections such as African swine fever virus. Scientists are trying to introduce specific DNA mutations into domestic pigs that are known to impart disease resistance to wild pigs in Africa, which do not cross breed with the European domestic pigs.
"Pig 26 has a specific single-base deletion. Out of its 3 billion bases, we have removed one exactly from where we wanted it to be removed. It's extremely easy to do," Professor Whitelaw said.
"This, in essence, is clean genetic engineering, if you want to call it that, and this is what is making commercial companies so excited and it's also going through the minds of the regulators at the minute to find a way of classifying it," he said.
Public opposition to GM food has halted the introduction of the technology in both crops and farm animals. However, a GM salmon could soon be the first GM animal to be declared officially safe to eat in the United States.
The powerful US Food and Drug Administration is near to making a decision on whether to allow Aquabounty Technologies of Massachusetts to produce its GM Atlantic salmon, which has an additional fish gene to make it grow faster all year round.
FAST-GROWING GM SALMON SET TO BE FIRST GM ANIMAL ON THE TABLE
The first genetically-modified animal approved for human consumption is likely to be a fast-growing GM salmon produced by Aquabounty Technologies of Massachusetts.
The US Food and Drug Administration (FDA) is expected to make a decision on the application later this year but has already ruled that there are no major health or environmental risks.
If approval is given, there are about 40 or 50 other GM animal proposals that will be put forward for regulatory approval, said Professor Helen Sang, who works on GM chickens at the Roslin Institute in Edinburgh.
"To feed a growing population that wants more meat in its diet will require all the tools we can lay our hands on to increase the efficiency of food production," Professor Sang said.
Professor Sang and her colleagues have already produced GM chickens that are partially resistance to influenza viruses, which are a huge problem for poultry farmers - 22 million chickens infected with H7N2 flu virus were slaughtered last year in Mexico alone.
"The GM chickens succumb to the disease themselves, but they don't transmit it on. This is just the first step using genetic modification in making birds completely resistant to flu and we are carrying on developing this approach," Professor Sang said.
"It's highlighted that you can use genetic modification to protect poultry, a very important food animal, in a way that cannot be achieved using conventional breeding," she said.
"We predict that this kind of genetic modification will protect against all strains of bird flu and we also predict that if we put this gene into pigs it would also protect against swine flu," she added.
Other GM animals include cows that produce milk with no beta-lactoglobulin, a protein linked with allergies in children. Chinese scientists are also working on GM cows that produce milk rich in omega-3 fats, normally found in fish.