Washington ? U.S. agriculture officials said Friday they had quarantined the offspring of the slaughtered Holstein cow that tested positive for mad cow disease amid an intensifying search for the stricken cow’s origins.

The government was trying to reassure the public about the safety of the U.S. food supply even as it confronted a wide ban on U.S. beef by countries that account for 90 percent of American beef exports.

The recall of more than 10,000 pounds of meat from the cow and others slaughtered Dec. 9 at the same Washington company also was continuing.

White House spokesman Scott McClellan said President Bush would continue to eat beef, adding that the president’s focus was “the public health aspect of this.”

The quarantine, which now includes herds at two Washington farms, was imposed even though officials said transmission of the disease from mother to calf was considered unlikely.

One calf is at the same dairy near Mabton, Wash., that was the final home of the diseased Holstein cow, said Dr. Ronald DeHaven, the Agriculture Department’s chief veterinarian. The other calf is at a bull calf feeding operation in Sunnyside, Wash., DeHaven said.

A third calf died shortly after birth in 2001, he said.

“The reason for concern with these calves is that even though it is an unlikely means of spreading the disease, there is the potential that the infected cow could pass the disease onto its calves,” he said. No decision has been made on destroying the herds.

The emphasis of the widening investigation is on finding the birth herd of the cow, since it likely was infected several years ago from eating contaminated feed, DeHaven said. Scientists say the incubation period for the disease in cattle is four or five years.

He said tracing the source of the infected cow could take days or weeks and extend to other states and even Canada.