Washington ? Agriculture Department officials said Wednesday that the dairy cow that tested positive this week for “mad cow” disease, a first in the United States, probably contracted the illness through feed containing tainted animal parts, despite a federal ban on putting such materials in cattle feed.

Federal officials continued to describe the health risk to consumers as extremely low, yet economic damage to the beef industry mounted. Additional trading partners placed import bans on U.S. beef, and investors dumped meat and restaurant stocks. Cattle prices tumbled by their maximum allowable level.

Agriculture Secretary Ann Veneman said Wednesday that the Holstein had come from a herd of about 4,000 dairy cows in southern Washington state, but federal officials said they presumed that the animal had contracted the disease through contaminated feed before joining that herd in October 2001. They were working to identify farms where it previously lived and other cattle that had shared the same feed supply.

The diseased cow was born about 1999, officials said, two years after a federal rule took effect that was designed to stop cattle from receiving tainted feed. Officials said they could not speculate whether a violation of the rule had led the animal to become infected.

The rule says cattle feed may not contain most proteins from mammals. It is intended to prevent a repeat of Britain’s “mad cow” crisis, in which the disease was thought to have infected more than 183,000 cattle in the 1980s and 1990s, primarily because proteins from diseased animals were fed to healthy ones.

Dr. Stephen Sundlof, director of the Center for Veterinary Medicine at the Food and Drug Administration, said compliance with the feed rule was only about 75 percent when it was enacted in 1997. It has since risen to 99 percent, he said.

The Agriculture Department also said the slaughterhouse that processed the diseased animal, Vern’s Moses Lake Meats of Moses Lake, Wash., had on Tuesday agreed voluntarily to recall all meat it handled Dec, 9, the day the animal was slaughtered. That meat may have been exposed to the infectious agent that causes “mad cow” disease, Veneman said.

Extensive recall

The recall covers 10,410 pounds of meat from the diseased animal and 19 others. Officials said they had identified three facilities where the carcasses underwent further processing after slaughter. But they were still working to locate the meat.

Late Wednesday, Albertsons announced that the recall affected some meat sold at stores in Washington state, Oregon and northern Idaho. No other Albertson stores were affected, the company emphasized.”People should continue to feel very confident in the safety of our meat supply,” Veneman said in a telephone news conference.

She and other officials emphasized that parts of the diseased animal considered most infectious — the spinal cord, brain and a portion of the small intestine — had never entered the food supply and that only the muscle meat, which is thought to harbor little or none of the infectious agent, was sent for processing into steaks, hamburger or other food products.

“The meats produced are cuts that would not be expected to be infected or have an adverse public health impact, but are being recalled out of an abundance of caution,” Veneman said.

Low risk but fatal

Known scientifically as bovine spongiform encephalopathy, or BSE, “mad cow” disease is caused by a poorly understood agent that creates holes in the brain, causing it to look like a sponge. Eating meat that contains the agent is thought to cause a human form of BSE, variant Creutzfeldt-Jakob disease, which has affected 153 people worldwide, nearly all in Britain. There is no known treatment for the disease, which is invariably fatal. Scientists do not know how long after eating infected meat a person may develop the disease, but it is probably “many years or decades,” according to the Centers for Disease Control and Prevention.

Agriculture Department officials first announced the “mad cow” findings Tuesday. They said the animal was “presumptive positive,” based on two tests that Veneman has called the “gold standard” for BSE detection. Samples were to arrive in Britain on Wednesday for confirming tests at a laboratory that specializes in the disease. Those tests will take three to five days.

Possibly isolated

Officials want to examine other animals that came from the “birth herd” of the diseased cow, as well as cattle it lived with elsewhere that may have eaten the same feed. But Dr. Ron DeHaven, the Agriculture Department’s chief veterinarian, said it was possible that no other cases would emerge.

“Even in those countries where the prevalence of the disease has been very high, it’s not uncommon at all — in fact, more common — that the number of animals that are infected within any herd is very small,” he said. “Very often, just one animal within a herd is found to be infected.”