The U.S. Department of Agriculture's (USDA) National Veterinary Services Laboratories (NVSL) in Ames, Iowa, has determined that the non-definitive test result reported on July 27 is negative for BSE. Tests conducted by the Veterinary Laboratories Agency in Weybridge, England, are also negative for BSE.
The furore began after the cow died and the USDA did not receive brain samples until July.
At the time the tissues were treated with a preservative and, when tested, produced a "non-definitive" result.
Many felt this was unsatisfactory and more tests were run at the USDA's national animal disease laboratory and by the Veterinary Laboratories Agency in Weybridge, England.
The tests ultimately showed the cow, which was at least 12 years old, did not have the fatal disease.
USDA Chief Veterinarian John Clifford said that the initial non-definitive test result was caused by artifactual staining and while the staining did not resemble mad cow disease, they felt the prudent course was to conduct additional tests.
They are very pleased with the final results.
Since December 2003 there have been two cases of mad cow disease in the U.S., one in Washington state, in a Holstein dairy cow imported from Canada, and the other in a beef cow in Texas.
According to scientists, the brain-destroying disease is caused by malformed proteins called prions.
People can become infected with a human version of the disease by eating contaminated beef products.