Researchers are inching their way toward producing cows that are immune to BSE but it's unlikely to result in herds of beef or dairy cattle with built-in resistance, according to an infectious disease expert in Saskatoon.

Scientists at Japan's Kirin Brewery and the U.S. biotechnology company Hematech genetically engineered 150 cow embryos that are resistant to bovine spongiform encephalopathy, the brain-wasting disease.

The cows won't carry the gene for misshapen prion protein that causes BSE, the companies said.

Chris Clark, an infectious disease expert at Western College of Veterinary Medicine in Saskatoon, said it is possible to produce a cow that is immune to BSE but he doesn't know how useful it would be.

First scientists would have to figure out what the prion protein does and what happens if it disappears.

"I know some of the British research groups are coming to the theory that they think that the prion protein may be important for what they call a scavenger probe," said Clark.

"What it may do is allow cells to kind of remove the natural waste materials that are produced by cellular metabolism and allow it to be recycled to prevent things accumulating."

The two companies developed the technique to produce pharmaceuticals in milk and have no plans to breed the cows for human consumption.

Clark said right now it is too costly and complicated to produce a BSE-immune cow that is viable for the beef and dairy industries.

There is a danger that introducing a genetically modified animal could cause the industry to lose hundreds of years of selectively breeding for good quality milk and beef, he said.

The risk of BSE in cattle can be virtually eliminated through strict controls over what they're fed, Clark said.