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Mad cow case raises questions about weaning calves on blood
January 29, 2004 The Kansas City Star by Scott Canon
Cattle infected with the disease carry nearly indestructible prion proteins in their brains, spinal cords and other central nervous tissues. The surest way to pass along the disease is to feed those slaughterhouse leftovers to cattle.
Yet cattle blood by the tankerload routinely leaves slaughterhouses to end up in a sort of infant formula for calves _ young livestock most vulnerable to mad cow infection.
The practice is among those the U.S. Food and Drug Administration is re-evaluating after the country's first confirmed case of mad cow disease last month, a spokeswoman said.
Blood poses yet another mad cow issue where the line between caution and panic is controversial.
"The information that we've got to date is that the blood is safe," said Larry Hollis, an extension beef veterinarian at Kansas State University. "If there was any hint that it wasn't safe, it would be banned."
Critics note that efforts to stop humans from passing a variant of the disease to each other prompted a ban on blood donations from potential human carriers.
They believe that weaning cattle on blood is taking an unwarranted risk, that it creates a public health hazard in order to help the cattle industry cut costs.
"In terms of how good a vehicle blood is (for passing the disease), it's not like brain matter or spinal cord," said Michael Greger, a physician working for the Organic Consumers Association. "If you inject mad cow brains into (laboratory) mice, all of them die ... But with blood it's on the order of one out of the 15 times. We know it happens."
The government sides with industry, allowing cattle blood in feed while barring anything else from slaughtered ruminants.
That's in line with a series of Harvard University studies concluding that the risk of passing the disease by feeding calves cattle blood runs so slight it defies calculation.
"I'm unwilling to say never," said George Gray, a biologist and toxicologist at the Harvard Center for Risk Analysis. "The risk is very, very low."
Dairy cattle pose a particular problem in containing mad cow disease. Bovine spongiform encephalopathy, or BSE, takes nearly four years to incubate and is unlikely to be passed on until then. In the United States, cattle raised strictly for beef typically head to slaughter before their third birthday. Dairy cows, however, live longer and pose a greater risk.
The two confirmed cases of mad cow disease in North America _ both came last year _ were dairy cattle. The last case was in a 6.5-year-old cow, likely sickened by feed as a calf in Alberta, Canada.
Cattle raised purely for beef typically spend their early days nurtured on the milk of their mothers. Cows in dairy herds, on the other hand, are otherwise occupied. So their young often wean on so-called calf starter or milk replacers made with cattle blood.
People in the beef industry make an emphatic case that experiments injecting cow brains with BSE-infected blood did not pass on the disease. So when the FDA adopted a ban on feeding animal parts to cattle in 1997, it left an exemption for blood.
"The agency believes (blood and blood products) represent a minimal risk," regulators concluded. "The excluded proteins and other items are materials that the available data suggest do not transmit" mad cow disease, the FDA said.
The United Kingdom saw its beef industry nearly collapse under more than 176,000 cases of mad cow and nearly 150 deaths from its human variation since 1989. Only when it banned feeding of all animal products, including blood, did it begin to contain its epidemic, said Steve Dealler, a microbiologist at the Lancaster Royal Infirmary.
"I hope the Americans are doing the right thing," said the physician, who has been studying the cattle and human variations of the disease since 1988. "But I don't think so."
It's possible, he said, that blood can become contaminated when bits of brain matter get knocked loose during slaughter.
Two methods thought most likely to pulverize brain matter _ one in which compressed air is injected into the brain, the other that deliberately pierces the brain stem _ are now outlawed. The preferred method of slaughter, the now common captive bolt stunning, uses an explosive charge that powers a rod into the skull. At least one study found that it causes less internal splattering of the brain. Contamination of the lungs and blood with brain matter can still happen. "However," researchers wrote, "the incidence appears to be very low."
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