Twenty-nine adult cows from the herd of the Texas cow infected with bovine spongiform encephalopathy, or Mad Cow disease, have been killed and are being tested for the disease.
The U.S. Agriculture Department says tissue samples were removed and will undergo screening referred to as a "rapid test." If results indicate the presence of Mad Cow disease, two additional tests will be done.
The rapid test that was done on the infected cow indicated the presence of the disease, but results from a different test were negative. USDA announced the animal was free of the brain-wasting disease.
USDA's internal watchdog then ordered a third type of test, which came back positive. A laboratory in England confirmed that finding last month.
The new case prompted a change in the government's testing policy. Now, both additional tests will be done if rapid tests indicate a sample is suspect.