..."We are looking at any and all appropriate changes we might make to our BSE surveillance program," Ron DeHaven, chief veterinary officer of the U.S. Department of Agriculture, said during a news briefing updating the mad cow investigation. Mad cow is also known as bovine spongiform encephalopathy or BSE.

Changes being considered include increasing the number of cattle that are screened for the disease and modifying the ban on feeding cattle tissue back to cattle -- a practice that is thought to spread mad cow disease among herds if the feed contains tissue from infected cattle.

DeHaven said the surveillance program in place to date has ensured the safety of the U.S. beef supply, but in light of the case of mad cow found in a cow on a farm in Mabton, Wash., earlier this month, "It's time to relook at that."

Efforts to track down the origin of the cow and about 10,000 pounds of beef that may have contained meat from the infected animal continued on Sunday.

The available information continues to indicate the animal came from Canada, DeHaven said. "We're continuing to work with Canadian officials to verify the trace back," he said, adding that media reports U.S. officials were in disagreement with Canadian authorities about the origins of the animal were unfounded.

"We are not in disagreement with our Canadian colleagues about the data we received," he said. Canadian officials said yesterday it was still too early in the investigation to conclusively determine the animal came from the Alberta province of Canada -- where a case of mad cow was identified in May.

DeHaven said the view is shared by the USDA. Indications about the origin of the animal are preliminary and "still not verified," he said.

However, he went on to say the investigation is focused on tracing down the other 73 head of cattle that came across the U.S border with the infected cow. In addition, U.S. and Canadian authorities are also conducting DNA testing to confirm the origin of the cow, he said.

The age of the animal is still in question. Initially, it was thought to be 4-1/2 years old based on U.S. records, but Canadian records indicate its age is closer to 6 1/2.

USDA authorities initiated a recall of 10,000 pounds of meat that may have contained tissue from the infected cow earlier this week, and efforts to track it down have revealed it went to grocery stores in eight different states and Guam, said Kenneth Petersen from USDA's Food Safety and Inspection Service.

Authorities said yesterday the meat had been distributed to Oregon, Washington, Nevada and California. New information indicates limited amounts also went to Alaska, Montana Hawaii, Idaho and Guam.

Some of the meat may have already been consumed, but Petersen said it was safe. "The recall was initiated out of an abundance of caution," he said. "We remain confident in the safety of these beef products ... and will continue to verify the distribution of all products related to recall."

However, surveys from the USDA's own Food Safety and Inspection Service going as far back as 1997 have found bits of spinal cord -which can carry the mad cow infectious agent - in meat processed by machines called advanced meat recovery systems. The infectious agent, known as a prion, can infect humans and cause a fatal brain-wasting condition called variant Creutzfeldt-Jakob disease.

The spinal tissue was thought to have been introduced into the meat in part due to the routine practice of splitting open the animal's spine during processing. Petersen said the Washington cow's spine had been split open prior to removing it from the carcass...

But the American system was never intended to keep sick animals from reaching the public's refrigerators, said Dr. Ron DeHaven, the Agriculture Department's chief veterinarian.

It is "a surveillance system, not a food safety test," Dr. DeHaven said in an interview on Wednesday.

Statistically, it is meant to ensure finding the disease only if it exists in one in a million animals, and only after slaughter.

December 24, 2003 Excerpts from USDA Briefing. Commentary: Michael Greger, M.D.

USDA Chief Veterinarian Dr. Ron DeHaven: "There is no scientific evidence to suggest that the disease is transmitted from mother to offspring."

On the USDA's own website they list the European Commission's report on maternal transmission which concludes, "The results of all epidemiological studies undertaken to date have been consistent with a rate of direct maternal transmission of approximately 10%..."