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DNA analysis to help locate mad cow source

"We're pretty confident that we have the herd, but we want to make sure."

John Clifford, US Department of Agriculture

The US government hopes DNA analysis can pinpoint the herd of the cow that tested positive for mad cow disease and lead investigators to the source of the animal's brain-wasting illness, the Agriculture Department's chief veterinarian said Saturday.

Genetic testing is needed because of mistakes in how the beef cow was labeled and how its tissues were stored, John Clifford told reporters in an interview.

The cow, a "downer" that could not walk, was delivered last November to a plant where animals unfit for human consumption are killed. The department has not identified the owner or the plant.

The cow's type of breed was mislabeled, possibly because the animal had been soiled heavily with manure, and its tissues were mixed with tissues from other cows, Clifford said.

"When we went back to this particular owner, the breed we identified, he indicated he did not sell that breed. He sold another breed," Clifford said. "In addition to that, we found that after the tissues were processed, there was some mixing."

Parts from the diseased animal and four other cows were supposed to be kept in separate waste barrels, but some of the waste was combined, Clifford said.

Department officials think they have found the right herd. To confirm that, they must find relatives of the dead cow and test DNA.

"We're pretty confident that we have the herd, but we want to make sure," Clifford said. "Testing is being done now on tissue from cows that may have been herdmates."

When he announced the mad cow test results on Friday, Agriculture Secretary Mike Johanns pointed out that US cattle "move all across the country."

"They might be born in one state; they might be fed to a certain weight in another state," said Johanns, a former governor of Nebraska, a major beef state. "They might be fed out in another state and slaughtered yet in a fourth state."

The new case was confirmed by an internationally recognized laboratory in England. A series of tests in the US had produced conflicting results.

US officials had declared the cow to be free of the disease in November, but the department's inspector general ordered a new round of tests that came back positive and led to the British tests.

It may be the first native-born case of mad cow disease. Johanns said there is no evidence the animal was imported. The only other US case, confirmed in December 2003 in Washington state, was in a dairy cow that had been imported from Canada, where three other cases have been found.

Like the 2003 case, the November cow was born before the 1997 feed ban, Johanns said.
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