Second possible case of mad cow in the U.S.

A second possible case of mad cow disease is making cattle producers in the United States fear for their livelihood as it could mean that U.S. beef could be again shunned by other countries.

The U.S. Agriculture Department (USDA) says that one of three suspect cows has tested positive for mad cow disease, and a second case was suspected in an older Texas cow. At this stage it is not known if it was imported, as was a cow of Canadian origin in Washington state confirmed positive for mad cow disease in 2003.

USDA secretary Mike Johanns says brain samples from the latest animal will be sent to the world's top mad cow lab in Weybridge, England, for final testing, he is hoping that this information will not impact on discussions with Japan, Korea or Canada regarding beef exports.

The greatest fear of course is of another global shutdown of beef markets from the U.S., as in 2003, but Johanns insists that U.S. beef is safe.

Beef producers in Australia say it is too early to predict how international markets will react to the positive test, but believe they are well placed to fill any extra demand.

It was hoped an 18-month ban on U.S. beef would be lifted later this year allowing the meat to re-enter Japan. The ban has given Australia a beef export boom.