The Agriculture Department said that additional checks were needed after an initial screening proved inconclusive for Mad Cow Disease in a single animal. The announcement raised fears that the U.S. might have its second case of the fatal brain-wasting disease and rattled the cattle industry, meat companies and hamburger restaurant chains.

Mad cow disease, bovine spongiform encephalopathy (BSE), attacks an animal's nervous system. People who eat food contaminated with BSE can contract a rare disease that is nearly always fatal -- variant Creutzfeldt-Jakob disease.

"The inconclusive result does not mean we have found another case of BSE in this country," said Andrea Morgan, associate deputy administrator of the department's Animal and Plant Health Inspection Service.

She said the department "remains confident in the safety of the U.S. beef supply."

The "inconclusive result" was the same term the agency used in June when two potential cases turned out to be false alarms.

Industry and consumer groups emphasized that the test results were preliminary and that no part of the animal in question had entered the food or feed chain.

Jan Lyons, a Kansas cattle producer who is the president of the National Cattlemen's Beef Association, said the test result "is simply one step in the process," and that a tissue sample was being tested at a national agricultural laboratory in Ames, Iowa.

"We can't assume at this point that this `inconclusive' represents a positive case," Lyons said.

The Consumer Federation of America suggested that the inconclusive label was misleading and that the government should have reported the findings as a "preliminary positive test."

Still, federation official Carol Tucker said, the announcement should not alarm consumers.

In the only confirmed U.S. case, a Canadian-born Holstein was found to have been infected in Washington state last December. More than 40 countries cut off imports of U.S. beef, and more than 700 additional cattle in Washington state, Oregon and Idaho were killed as a precaution.

Ranches and businesses dependent on beef are still feeling financial effects from that episode. The most-recent announcement sent cattle prices tumbling. Shares of McDonald's, Wendy's and other restaurant chains that feature hamburgers slumped, as did those of U.S. meat producers such as Tyson Foods Inc.

The government gave no information about the location or origin of the slaughtered animal, and the announcement led to a flurry of assertions by state agriculture officials that the animal did not come from their states.

The department said in a statement that information about the animal and origin would be released only if the tests come back positive. "These tests cast a very wide net, and many end up negative during further testing," the statement said.

The agency says it has performed rapid screening tests on over 113,000 cattle since an enhanced surveillance program began June 1 on cattle considered at high risk for BSE.

Alisa Harrison, a department spokeswoman, said the animal in question was one of these high-risk animals. This group includes animals that died on the farm, have trouble walking or showed signs of nerve damage.

The announcement comes less than a month after U.S. negotiators reached tentative agreements with both Japan and Taiwan to resume U.S. beef and beef product shipments.

Morgan told reporters that she did not anticipate the announcement would undermine those negotiations because of safeguards already in place and "measures that we have already taken to date."

Exports represent about $3.8 billion of America's $40 billion a year beef industry.

The American Meat Institute (AMI) assured that U.S. beef is safe and consumers need not worry about news of a new "inconclusive" test result for BSE.

"Inconclusive test results are just what they sound like -- inconclusive," said AMI president J. Patrick Boyle. "Regardless of the outcome of this test result, U.S. beef is safe."

Boyle urged consumers and the media to remember that:

-- If this test result is positive, consumers need not worry, because the infective agent has never been detected in beef -- only in parts of the animal that are removed and not permitted to be sold for human consumption.
-- In addition, consumers may be reassured to know that USDA announced that beef from this animal was not released into commerce.
-- The U.S. took proactive measures more than a decade before a single case was detected in an imported cow in 2003. These measures ensure that any case of BSE will be rapidly detected and contained and the public health will be protected.
-- More than 113,000 high-risk cattle have been tested for BSE since June under USDA's enhanced surveillance program. To date, none have been positive.

"Consumers should have absolute confidence in the U.S. government's ability to respond to this inconclusive test result swiftly and thoroughly," Boyle said. "If the test ultimately is positive, it must be treated as an animal health issue, not a public health concern. In fact, expert scientists say that thanks to U.S. efforts to protect cattle from this disease, the risk that BSE poses to consumers is so low it can scarcely be quantified."