USDA officials said they completed their field investigation of the group of animals believed to have been transported with a Canadian dairy cow that tested positive for bovine spongiform encephalopathy or mad cow disease in early December.
The investigation involved the identification of more than 75,000 animals in three states, said Ron DeHaven, deputy administrator of veterinary services for USDA's Animal and Plant Health Inspection Service. None of the other animals found to have been in the herd tested positive for BSE.
DeHaven said the inquiry, which involved APHIS personnel examining animals in 189 separate investigations, gave further proof that the BSE-positive cow slaughtered in Washington state on Dec. 9 was born on a dairy farm in Calmar, Alberta, Canada, on April 9, 1997.
She was moved to the United States in September 2001 along with 80 other cattle from that dairy.
"The epidemiological investigation to find additional animals from the source herd led to a total of 189 investigations leading to complete herd inventories on 51 premises in three states: Washington, Oregon and Idaho," he said.
DeHaven said the field investigation involved a total of 255 "animals of interest" on 10 premises in Washington, Oregon, and Idaho.
"Animals of interest are defined as animals that were — or could have been — from the source herd in Alberta, Canada," he said.
Of the 255 animals of interest, investigators traced 28 back to the group of 80 cattle that entered the United States with the BSE-positive cow, as well as seven heifers out of a group of 17 heifers which were also known to be from the source herd.
Investigators do not believe all 17 entered the United States, but all of them would be considered minimal risk and not significant to the investigation.
"Guidelines on bovine spongiform encephalopathy issued by the World Organization for Animal Health (OIE), the international animal heath standard setting organization, state that animals born on a premises within one year (before or after) of a BSE-affected animal should be considered of greater risk to the country reporting the BSE detection," said DeHaven.
"As such, USDA has focused on 25 of the 81 animals also born into the birth herd of the index animal. Based on normal culling practices of local dairies, APHIS estimated that the Agency would be able to locate approximately 11 of these animals. APHIS definitively located 13 of these animals, plus the index or BSE-positive cow, for a total of 14.
"We feel confident that the remaining animals represent very little risk. Even in countries like the United Kingdom where the prevalence of BSE has been very high, it is very uncommon to find more than one or maybe two positive animals within a herd.
"We have had an effective feed ban in place for over six years, thus preventing the transmission of the disease to other animals," DeHaven noted.
USDA officials said that more than 2,000 tons of meat and bone meal being held due to potential contamination with protein from the positive cow is on hold and will soon be disposed of in a landfill in accordance with all federal, state, and local regulations.