"Needless to say, we are very pleased with these results," said John Clifford, the Agriculture Department's chief veterinarian.

It was a quirky case in the prolonged and costly fight to stamp out the highly unusual disease, bovine spongiform encephalopathy, or BSE.

Veterinarian Forgot?

While enduring criticism for the handling of a Texas cow that was found positive for BSE seven months after it was confirmed negative, the department disclosed last week that a private veterinarian had "forgotten" about a brain tissue sample taken in April from a cow with suspicious calving problems. The USDA did not disclose the cow's location.

Cows with calving paralysis are typically considered downers -- alive, but unable to walk -- that require BSE testing under federal guidelines.

The chemicals used by the unnamed veterinarian to preserve the sample made it impossible for animal protection investigators to run an initial screening test, known as rapid BioRad.

Instead, an immunohistochemistry test was made and the result carried tell-tale staining that shows up when BSE is present. But this came in an abnormal pattern, Clifford said earlier.

Wednesday, he explained that the initial non-definitive result was caused by "artificial or untrue" staining. "And while this staining did not resemble BSE, we felt the prudent course was to conduct the additional tests."

'Twists and Turns'

"Through all the twists and turns of this saga, we continue to come to the conclusion that thew US beef supply is safe and the nation's herd is free of BSE," said Matt Brockman, executive vice president of the Fort Worth-based Texas and Southwestern Cattle Raisers Association.

The first case, a Canadian-bred dairy cow, was discovered in Washington state in December 2003. The second was the native-born Texas beef cow whose BSE contamination was confirmed June 24.

At no time was the US food supply at risk, since both carcarsses were incinerated. Both animals were born before the 1997 ban on cattle feed made from rendered cattle parts, a product scientists believe spread the disease. The vast majority of beef now consumed comes from cattle born after 1997.

A rare human disease, variant Cretuzfeld-Jacob, is believed contracted from BSE-tainted beef. The only US case involved a Florida woman who lived in Britain when BSE-contaminated beef products were sold.