A House committee is challenging the Agriculture Department's view that the nation's first cow sick with deadly mad cow disease (search) was lame.

Contrary to the department, three eyewitnesses at the Washington state plant where the Holstein (search) was slaughtered on Dec. 9 say the cow appeared healthy, lawmakers on the House Government Reform Committee said in a letter Tuesday to Agriculture Secretary Ann Veneman.

The issue is significant because Agriculture Department officials that monitor meat plants target "downer" (search) cattle — animals that are sick, injured or that exhibit symptoms of disease — for testing of mad cow, a brain-wasting illness. Critics have argued that the agency needs also test healthy animals as a safeguard against the illness, which can incubate for four or five years.

Committee chairman Tom Davis, R-Va., and Rep. Henry Waxman, the senior Democrat on the committee, questioned the adequacy of the government's mad cow testing program.

"If the new information is accurate, USDA's surveillance system may need to be significantly expanded," they said.

"The new information also raises questions about USDA's credibility," wrote Davis and Waxman, of California. "The American people need to have confidence in what USDA (search) reports about the safety of the food supply."

Tom Ellestad manages Vern's Moses Lake Meats (search), the small meat plant in Moses Lake, Wash., where the cow was slaughtered. He says the dairy cow was able to walk.

"The BSE-positive cow was not a downer," he said in an affidavit given to a watchdog group, the Government Accountability Project, which was cited in the lawmakers' letter.

In a telephone interview Tuesday with The Associated Press, Ellestad said everything in his 18-page affidavit taken by GAP and cited by the House committee is accurate.

A USDA veterinarian had labeled the cow as a downer, but Ellestad said that after the vet made the notation in the paperwork, the animal stood up again, according to his statement to GAP.

Ellestad said tissue from the Holstein was sent for testing because Vern's had a contract with USDA that allowed it to send samples from healthy animals, not because it was a downer, Ellestad said.

The department maintains that the animal was a downer, and says its testing program was effective in helping it find the second known case of bovine spongiform encephalopathy (search), or BSE, in North America. The first case turned up in Canada last May.

Agriculture Department spokesman Steve Cohen said Tuesday that the infected Holstein was unable to walk at the plant, and department veterinarian at the plant tagged it as a downer. He said he did not know whether the plant had the separate contract for testing that Ellestad mentioned in his affidavit.

Cohen also said another cow that day initially was classified as a downer, but then was reclassified as ambulatory after it got up. He said he was not in a position to tell if the people who handled the Holstein had mistaken it for another.

Ellestad, asked if a case of mistaken identity was possible, said, "No."

Another witness, David Louthan, recalls killing the animal. "That was a walking cow," he told the Washington state Legislature's House and Senate agriculture committees at Feb. 3 hearings.

Randy Hull, the hauler, said in a statement in January that he loaded three cows from the Sunny Dene Dairy farm for delivery to the meat plant. "The animals each walked onto my trailer," he said.

After the case was confirmed Dec. 23, Veneman doubled from 20,000 to 40,000 the number of cattle to be tested annually for mad cow disease. But an international panel she appointed and a Food and Drug Administration (search) advisory committee have said testing needs to go far beyond that.

The department's inspector general's office is investigating how the case was handled.