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 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, Calif. 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.
However, USDA spokesman Matt Herrick said investigators are laboring through paper records. That fact, combined with the fact that the cow was more than twice as old as most milk cows in the system, could indicate one of the region's smaller dairies is the target of the probe.
The World Organization for Animal Health has established protocol for investigations into cases of bovine spongiform encephalopathy that includes finding other cows that the Holstein in question was raised with, tracking down all progeny and determining what she ate.
After the UK crisis, federal regulations changed to keep brains and spinal columns in cattle over 30 from being rendered into protein products for human consumption. In addition, bovine protein is not supposed to be fed to other bovines.
However, bovine protein is routinely fed to egg-laying chickens, and the "litter" from those chickens _ chicken excrement and the feed that spills onto the floor _ is collected and rendered back into cattle feed. Neurodegenerative researchers such as UC San Francisco's Dr. Stanley Prusiner, who received the 1997 Nobel Prize in Medicine for discovering prions _ the protein associated with BSE _ has warned that the US should ban poultry waste in cattle feed.
Most dairy cows typically experience declining milk production by age 5 and are sent to slaughterhouses to be ground into hamburger. The FDA tests 40,000 of the nation's 35 million slaughtered dairy and beef cattle annually for BSE, targeting animals older than 30 months, when the disease is more likely to appear. However, there are cases of BSE that have been detected in cattle as young as 20 months.
"We are testing .12 percent of the cattle slaughtered," Michael Hansen, senior scientist at the Consumers Union and a longtime critic of the US policy regarding mad cow disease. "In Japan they test all cattle over 20 months, in Europe it's all cattle over 24 or 30 months, depending on the country. They've been able to find sick animals that look healthy but could have ended up in the food supply."
A move by a Kansas beef packer in 2006 to voluntarily test all of its beef so it could label the packages "BSE free," was thwarted by the USDA, which argued that it would create instability in the market. Creekstone Farms Premium Beef had challenged the USDA's position that it held legal authority to control access to the test kits.
In the current case, the USDA didn't elaborate on the cow's symptoms other than to say it was "humanely euthanized after it developed lameness and became recumbent." Outward symptoms of the disease can include unsteadiness and incoordination.
The unidentified Tulare County dairy where the cow died was not under obligation to report its suspicious behavior, according to state and federal agriculture officials, because the symptoms mimic other neurological diseases that can afflict cattle, said Dr. Richard Breitmeyer, director of the California Animal Health and Food Safety Laboratory at UC Davis.
"In reality (mad cow disease) is so rare in this country and there are just very little in the way of clinical signs specific to BSE alone," said Breitmeyer, who spent 17 years as California's state veterinarian.