Spokane -- Preliminary results of an investigation into cow deaths at a Stevens County dairy found no evidence of foreign animal disease infection or mad cow disease, a Washington State Department of Agriculture spokesman said.

State Veterinarian Dr. Leonard Eldridge and agriculture investigators visited the farm, where 50-60 animals have died over the past several months, spokesman Jason Kelly said Thursday.

Mad cow disease - bovine spongiform encephalopathy or BSE - is a brain wasting disease in cattle that is thought to spread to humans through eating infected meat products.

"The investigators found no evidence of foreign animal disease infection or clinical evidence of BSE," Kelly said in a release.

"This was not a sudden animal death event. The farmer reported to investigators 50 to 60 animal deaths over the last several months," he said. "The WSDA investigation found evidence consistent with that information."

Kelly said state investigators previously had been at the dairy near Addy, about 75 miles north of Spokane and about 50 miles south of the Canadian border. No milk had been sold or distributed there since December, Kelly said.

The investigation was prompted by reports that dead animals were seen at the dairy. "Reports prompted us to begin an animal health investigation," he said.

Officials from the U.S. Department of Agriculture and U.S. Food and Drug Administration were aiding the ongoing investigation, Kelly and others said.

Alan Bennett, a spokesman with the FDA in Portland, Ore., said his agency has been in contact with state agriculture officials, but noted it is not uncommon for the agency to work with state officials.

BSE is a chronic, degenerative disease of the brain and spinal cord in cattle. Cattle can get the disease through contaminated meat and bone meal fed to the animal as a protein source.

It's thought that people eating infected beef can contract the human variant of the disease.

The first U.S. case of the deadly brain-wasting disease was found in a Mabton dairy cow in December 2003. The herd was destroyed and that cow's origins were later traced to Canada, where it was believed to have eaten contaminated feed.