A bacon sandwich for slimmers

A new breed of healthy transgenic pigs has been created to produce leaner meat. The swine, which have been bred successfully through two generations from the creation of their genetically modified grandfather, represent a breakthrough in the effort to engineer animals that might one day wind up on the dinner plate.

The advance has been made by a team of experts at the United States department of agriculture's gene evaluation and mapping laboratory in Beltsville.

Earlier attempts by the same group ran into problems that resulted in arthritic, impotent pigs that could barely move and provoked angry reactions from animal rights campaigners.

Vernon Pursel, who has led the project,

announced his latest results at a recent conference on genomics in California.

"There is no question that we can put a gene into an animal that can be transmitted to the next generation and has a positive effect on the carcass composition," he said.

The pigs' DNA was altered to carry a gene that produces insulin-like growth factor-I (IGF-I), a chemical that stimulates tissue growth. This gene was, however, only active in striated muscle - other tissue remained unaffected.

This made their meat up to 12 per cent more lean while the loin, where the most expensive meat is found, was up to 30 per cent larger. Carcass quality was also improved in previous transgenic pigs that were injected with a growth hormone gene.

However, those animals also suffered a range of health problems triggered by raising growth hormone levels throughout the body. The new pigs, where IGF-I activity was restricted to striated

muscle, were not afflicted with the same difficulties.

In Dr Pursel's tests, the transgenic pigs and the next two generations produced by breeding with conventional animals developed normally in all respects other than they possessed more muscle and less fat.

However, despite the project's success, there are no plans for any of the pigs involved to be eaten - the experiment was intended to confirm the feasibility of the technology involved.

"It is a proof of concept and if society says we don't want this, maybe this will never go into production," said Dr Pursel.

The team is now investigating how to make further improvements to the quality of the meat.