The Agriculture Department is investigating a possible case of mad cow disease. Tests are being conducted in Ames, Iowa and results should be completed within a week.

The investigation does not mean a new case of mad cow has been found.

The agency's chief veterinarian said the cow did not enter the human or animal food chain. In humans, eating meat products contaminated with mad cow disease has been linked to more than 150 deaths worldwide from variant Creutzfeldt-Jakob disease, a rare and fatal nerve disease.

A majority of the deaths were in Britain, where there was an outbreak of mad cow disease that started in the mid-1980s. Just this week, European Union food safety experts agreed to lift a 10-year beef export ban imposed on Britain at the peak of the 1990s mad cow scare, giving a boost to its struggling beef industry.