FRESNO — The California dairy cow found to have mad cow disease was very old for a milk producer and had been euthanized after it became lame and started lying down, federal officials revealed in their latest update on the discovery.
The 10-year-old dairy cow, only the fourth such animal ever discovered in the United States, was found as part of an Agriculture Department program that tests about 40,000 cows a year for the fatal brain disease. It was unable to stand before it was killed and sent to a rendering plant’s Hanford transfer station.
It was one of dozens that underwent random testing at the transfer site, and the positive results have set off a federal investigation into the source of the disease.
U.S. health officials say there is no risk to the food supply. The California cow was never destined for the meat market, and it developed “atypical” BSE from a random mutation, something that scientists know happens occasionally. Somehow, a protein the body normally harbors folds into an abnormal shape called a prion, setting off a chain reaction of misfolds that eventually kills brain cells.
A USDA spokesman says they do not yet know what causes this strain of the disease. Agriculture officials are investigating, among other things, whether feed sources might have played a role in the animal contracting the fatal illness.
The strain of bovine spongiform encephalopathy that appeared in the UK in the 1990s and set off a worldwide beef scare was a form caused by cattle eating rendered protein supplements derived from slaughtered cattle, including brains and spinal columns, where the disease is harbored. Scientists know less about the “atypical” strain.
It “may or may not be related to feed or forage type,” said Larry Hawkins, spokesman for the USDA’s Animal and Plant Health Inspection Service in California.
The dairy in question is one of 381 in Tulare County, the No. 1 dairy county in the nation. Most mega-dairies have computerized records which would allow investigators to easily track any offspring the cow had in order to keep up her milk production.