'Forgotten' sample tests positive for mad cow disease.

Byline: Barry Shlachter

Jul. 28--The Agriculture Department said Wednesday that a "forgotten" brain sample taken in April from an ailing cow was tested last week and gave a positive but unusual reaction for mad cow disease.

The department said it is too early to call it the nation's third case of bovine spongiform encephalopathy, or BSE. The cow's herd has not been quarantined, nor have its progeny and similar-age livestock been traced.

Officially, the test was "nondefinitive." The USDA said staining on the sample denoted prion proteins of BSE, but not in places where such stains usually occur.

Further testing will be conducted at laboratories in Ames, Iowa, and Weybridge, England, with results expected next week, said John Clifford, the USDA's chief veterinarian.

The animal, killed after experiencing calving problems, was incinerated, and there was no risk to the food supply, Clifford said during a teleconference.

Clifford said early reports indicated that the cow was native-born, but he would not say where its herd was. Texas Animal Health Commission officials said they have not been contacted, The Associated Press reported. Texas has the nation's largest cattle herd.