However, USDA did say that meat from the animal has not entered the food or livestock feed supply.

Mad cow disease is name commonly used to describe Bovine Spongiform Encephalopathy (BSE), a slowly progressive, degenerative and fatal disease that affects the central nervous system of adult cattle.

Humans who eat meat from a diseased animal are at risk of contracting a deadly form of the brain-wasting disease, Creutzfeldt-Jakob Syndrome.

One Prior Confirmed Case

Since 1990, the U.S. Department of Agriculture (USDA) says it has conducted aggressive surveillance of the highest risk cattle going to slaughter in the United States. Prior to the current suspected case, the only cow that had been found to be affected with BSE was one diagnosed in December 2003.

The U.S. beef industry has not fully recovered from the financial setbacks due to that occurrence. Thursday's news sent cattle prices plummeting on fears that demand for U.S. beef exports would decline further. Shares of McDonald's, Wendy's, and other hamburger restaurant chains fell.

Inconclusive Result

Andrea Morgan, Associate Deputy Administrator Animal and Plant Health Inspection Service, U.S. Department of Agriculture, issued the following statement on Thursday:

"Early this morning, we were notified that an inconclusive BSE test result was received on a rapid screening test used as part of our enhanced BSE surveillance program.

"The inconclusive result does not mean we have found another case of BSE in this country. Inconclusive results are a normal component of screening tests, which are designed to be extremely sensitive so they will detect any sample that could possibly be positive.

"Tissue samples are now being sent to USDA's National Veterinary Services Laboratories - the national BSE reference lab - which will run confirmatory testing.

"Because this test is only an inconclusive test result, we are not disclosing details specific to this test at this time.

No Contamination of Food Chain

"APHIS has begun internal steps to begin initial tracebacks, if further testing were to return a positive result. However, it is important to note that this animal did not enter the food or feed chain.

"Confirmatory results are expected back from NVSL within the next 4 to 7 days. If the test comes back positive for BSE, we will provide additional information about the animal and its origin.

"USDA remains confident in the safety of the U.S. beef supply. Our ban on specified risk materials from the human food chain provides the protection to public health, should another case of BSE ever be detected in the United States.

BSE Not Unexpected

"Screening tests are often used in both human and animal health and inconclusives are not unexpected. These tests cast a very wide net and many end up negative during further testing.

"And some subset of these animals may even turn out to be positive for BSE. While none of us wants to see that happen, that is not unexpected either. Our surveillance program is designed to test as many animals as we can in the populations that are considered to be at high risk for BSE.

"Additional measures to strengthen public health safeguards include

• the longstanding ban on imports of live cattle, other ruminants, and most ruminant products from high-risk countries;

• FDA's 1997 prohibition on the use of most mammalian protein in cattle feed;

• an aggressive surveillance program that has been in place for more than a decade;

• the banning of non-ambulatory cattle from the human food chain;

• the process control requirement for establishments using advanced meat recovery (AMR) systems;

• prohibiting the air-injection stunning of cattle;

• and, if an animal presented for slaughter is sampled for BSE, holding the carcass until the test results have been confirmed negative."