Holstein calves killed as a precautionary measure against mad cow disease (search) were buried Wednesday at a landfill, a disposal method that state officials said will protect the public from any possible health threat.

A snowstorm had delayed federal officials' plans to bury the herd of 449 calves Wednesday, but by late afternoon two trucks containing the animals had pulled up to the southern Washington landfill.

"They had a break in the weather and [the calves] were taken to the landfill," U.S. Department of Agriculture (search) spokesman Nolan Lemon said Wednesday evening. "By this time, they probably have been buried."

USDA veterinarians and other federal workers finished sedating and lethally injecting the herd at a vacant slaughterhouse in northeast Washington late Tuesday, Lemon said.

The calves were part of a herd that included the offspring of a Holstein (search) infected with mad cow disease that came from Canada. The Holstein, slaughtered Dec. 9, was diagnosed with mad cow disease Dec. 22, becoming the first and only cow in the United States found with the brain-wasting illness.

Agriculture officials said the herd had to be killed because the calf born to the sick cow was not tagged and could not be identified. They have been unable to rule out the possibility that mad cow disease can be transmitted from mother to calf.

The infected cow was born at a dairy farm in the Canadian province of Alberta and came to the United States two years ago. The only other case of the disease in North American-born cattle was discovered in May in a cow from an Alberta herd.

Several Democrats, including Senate Democratic leader Tom Daschle of South Dakota, announced their support Wednesday for testing all cattle at slaughter. USDA officials have said they are considering a range of options, including more extensive testing.

Daschle also joined with other lawmakers from the Midwest in calling on Agriculture Secretary Ann Veneman to close the border to all Canadian beef products for the time being.

"We need to get as much information about the safety of products from Canada as we can," he said in Washington, D.C. "The only way to do that effectively is to shut down the border."

The United States restricted imports of Canadian beef after the May case of mad cow, but reopened the border to some beef cuts in October. Canadian officials and cattlemen are pushing for the further opening of markets.

"Science dictates that these markets should be open to Canadian beef," Prime Minister Paul Martin said.

The landfill where the USDA planned to dispose of the calf carcasses is considered one of the most secure in North America, according to Rabanco Regional Disposal, a Seattle company that contracts with Klickitat County to operate it.

"Once we get them covered up, the risk is very close to zero," said Kevin Barry, the county's director of public health. His agency regulates the landfill, near Roosevelt and about 60 miles south of Yakima.

There is virtually no chance for the rogue proteins called prions that are believed to cause the disease to escape the landfill, Barry said. The landfill, lined with plastic and clay about 1,500 feet above the region's aquifer, is expected to operate until about 2040, then be capped and covered with many feet of dirt, he said.

Landfill workers burying the calves were not required to wear any special protection, such as respirators or clothing, and the earth-moving machines will not need to be disinfected, Barry said.

"With an intact carcass, there really is no risk at all," he said.

Mad cow disease, or bovine spongiform encephalopathy, eats holes in the brains of cattle. The disease is a concern because humans can develop a brain-wasting illness, variant Creutzfeldt-Jakob disease, from consuming contaminated beef products.

Officials have said they believe the cows probably were infected as calves because they were born before August 1997, when the United States and Canada banned cattle feed that contained parts of cattle, sheep or other cud-chewing animals.