The Bush administration said Tuesday it will fight to keep meatpackers from testing all their animals for mad cow disease.

The Agriculture Department tests less than 1 percent of slaughtered cows for the disease, which can be fatal to humans who eat tainted beef. But Kansas-based Creekstone Farms Premium Beef wants to test all of its cows.

Larger meat companies feared that move because, if Creekstone tested its meat and advertised it as safe, they might have to perform the expensive test, too.

The Agriculture Department regulates the test and argued that widespread testing could lead to a false positive that would harm the meat industry.

A federal judge ruled in March that such tests must be allowed. U.S. District Judge James Robertson noted that Creekstone sought to use the same test the government relies on and said the government didn't have the authority to restrict it.

The ruling was to take effect June 1, but the Agriculture Department said Tuesday it would appeal — effectively delaying the testing until the court challenge plays out.

Mad cow disease, or bovine spongiform encephalopathy, is linked to more than 150 human deaths worldwide, mostly in Britain.

There have been three cases of mad cow disease in the U.S. The first, in December 2003 in Washington state, was in a cow that had been imported from Canada. The second, in 2005, was in a Texas-born cow. The third was confirmed last year in an Alabama cow.