N.Y. Times News Service Mar 11, 1997
Mad cow outbreak may have been caused by animal rendering plants
When cows in Britain began staggering around and dying, their brains eaten away by a mysterious disease, officials in the United States were reassuring. The disease would not be a problem here, they said. Later, when it appeared that a few people in Britain had contracted a similar lethal condition from eating affected meat, experts at the Department of Agriculture said there was no reason for Americans to worry.
Now, though, the Food and Drug Administration is starting to talk about new regulations in the aftermath of disturbing hints that something similar conceivably could appear in American animals. So far, the only affected animals are a few hundred mink in Wisconsin. Nevertheless, the agency wants to restrict the little-known agricultural practice that lies behind the problem in Britain: the use of rendered animal tissue in animal feed. In the process, they are drawing new attention to rendering -- the ancient but seldom-discussed practice of boiling down and making feed meal and other products out of slaughterhouse and restaurant scraps, dead farm animals, road kill and -- distasteful as it may seem -- cats and dogs euthanized in some animal shelters.
This quasi-cannibalism lies behind the outbreak in Britain and regulators want to be sure it will not cause problems in the United States. The disease that struck the British cows, bovine spongiform encephalopathy, may have originated as scrapie, a mysterious condition limited to sheep. Scientists believe the so-called mad cow disease results when cattle eat feed made from the brains or spinal cords of sheep suffering from scrapie. They believe the people who died were infected when they ate beef or other products from these cows, a theory that remains controversial, though evidence is accumulating.
Public health officials and agricultural experts say there are good reasons to believe that mad cow disease will not become a problem in the United States. Scrapie is less common in this country than in Britain. More importantly, the Food and Drug Administration is moving to ban the use of certain animal tissues in cattle feed. The agency recently held hearings on the effects that such a ban might have on the billion-dollar industry and hopes to decide this year whether to impose a ban.
Rendering, which dates to the early Egyptians, operates in the shadows of polite society, persisting because it provides an essential service: disposing of millions of pounds of dead animals every day.
"If you burned all the carcasses, you'd get a terrible air pollution problem," said Dr. William Heuston, associate dean of the Virginia-Maryland College of Veterinary Medicine at College Park, Md. "If you put it all into landfills, you'd have a colossal public health problem, not to mention stench. Dead animals are an ideal medium for bacterial growth."
Renderers in the United States pick up 100 million pounds of waste material every day -- a witch's brew of feet, heads, stomachs, intestines, hooves, spinal cords, tails, grease, feathers and bones. Half of every butchered cow and a third of every pig is not consumed by humans. An estimated six million to seven million dogs and cats are killed in animal shelters each year, said Jeff Frace, a spokesman for the American Society for the Prevention of Cruelty to Animals in New York City.
For example, the city of Los Angeles sends 200 tons of euthanized cats and dogs to West Coast Rendering, in Los Angeles, every month, according to Chuck Ellis, a spokesman for the city's Sanitation Department. Pet food companies try not to buy meat and bone meal from renderers who grind up cats and dogs, said Doug Anderson, president of Darling International Inc., a large rendering company in Dallas. "We do not accept companion animals," he said. "But there are still a number of small plants that will render anything."
At least 250 rendering plants operate in the United States, said Bruce Blanton, executive director of the 130-member National Renderers Association in Alexandria, Va. While there are still a few small operations on the outskirts of some cities, he said, modern rendering plants are large and centralized, and the industry's revenues amount to $2.4 billion a year.
After trucks deliver the wastes to the plants, the material is minced and fed into a vessel where it is steam-cooked to 250 degrees or more, and then the stew is cooked for 20 to 90 minutes, Blanton said. In the resulting mash, heavier material drops to the bottom and the lighter stuff floats to the top. Fat is siphoned off the top, filtered and sent through centrifuges to further refine it, Blanton said. Chemical manufacturers turn much of it into fatty acids for lubricants, lipstick, cement, polish, inks and waxes. Other fractions, including gelatinous layers, tallow and grease, go into thousands of products, including soaps, candles, pharmaceuticals, homeopathic medicines and gummy candies.
The heavier protein material on the bottom goes through a separate process, Blanton said. It is dried, squeezed to remove more fat and dried again. The resulting powder is the major ingredient in pet and animal feed. It is a cannibalistic practice that has proved highly profitable.
"We are the original recyclers," said Dr. Don A. Franco, a veterinarian and director of scientific services for the Animal Protein Producers' Industry, another trade group representing rendering firms. "We recycle 40 billion pounds of material a year."
Mad cow disease erupted in Britain because of a number of factors there, said Dr. Linda Detweiler, a veterinarian with the United States Agriculture Department's Animal and Plant Health Inspection Service in Trenton. Unlike the United States, Britain has a large sheep population relative to cows and a serious problem with scrapie, a transmissible, slowly progressive degenerative brain disease of sheep.
Many scientists who have studied the problem now believe that scrapie somehow crossed a species barrier to infect cows, possibly when the cows ate feed composed in part of brain tissue from infected sheep. The disease presumably jumped to people who ate infected cow brains. Current theory holds that some people may have genes that make them particularly susceptible.
Mad cow disease was first recognized as a cattle disorder in November 1986. Since then more than 165,000 cows have been affected. Heuston said renderers were shocked to learn that an agent like scrapie might survive the rendering process.
But British rendering practices may have helped spread the disease, said David Evans, president of Carolina Byproducts, a rendering company in Greensboro, N.C. There are people in Britain, called knackers, who make a living going around the countryside picking up dead animals and rendering them in their backyards. The fat they obtain brings good money from chemical firms, he said.
These knackers simply grind up and partly cook their daily haul to break fat cells and collect the gunk from the top of their vats. The remaining material, called greaves or crackling, was sold to farmers who then mixed it with grain and fed it to their animals. This material, some derived from sheep with scrapie or cattle with mad cow disease, was fed in large amounts to dairy herds in the late 1980s, Detweiler said.
Yet another factor lay in the way greaves were processed in conventional rendering plants, Anderson said. Until the early 1980s, many renderers had used flammable solvents to dissolve fats and the solvents may have deactivated the agent that causes mad cow disease and scrapie. But after several plant explosions, the companies switched to other methods that appear not to deactivate the agent -- a mysterious particle called a prion.
Since 1989, British renderers have tried to keep infected meat out of their products, many knackers have gone out of business and brains are no longer put into hamburger. But the incubation for the human disease is 7 to 30 years, Evans said. While only 15 cases of human disease have been confirmed, many experts fear a latent epidemic.
In 1989, the American rendering industry initiated a voluntary program under which, for example, no sheep heads were to be accepted at rendering plants. An Agriculture Department survey three years later found that 6 of 11 plants inspected still did accept sheep heads. Nevertheless, many experts feel that American shores are safe from mad cow disease, especially if scrapie is the underlying vector. In Britain, sheep account for 14 percent of raw rendering material. Here it is 0.6 percent and most of that material is free from scrapie.
The reason is that scrapie is closely monitored by United States Agriculture Department veterinarians under a federal program. There are no knackers in this country and no greaves to infect cattle, Detweiler said. Few ranchers here feed meat and bone meal to young cows and American renderers usually treat the raw material at higher temperatures.
But the key element in efforts to prevent the cow disease is a newly proposed Agriculture Department ban on feeding protein derived from ruminant animals to other ruminants. Ruminants are animals that chew cuds, including cows, sheep, goats, deer and elk. Mink are included in the ban because they can be affected by a disorder similar to mad cow disease.
If the Agriculture Department rules are adopted, cow protein might still be fed to fish, chicken or pigs in hope that if mad cow disease were to appear, a species barrier would stop it from spreading. At the same time, the Agriculture Department continues to monitor American cows for signs of mad cow disease. Scientists have examined the brains of 5,342 cows that displayed symptoms of central nervous system disease; no cases have been discovered.
But a major reason to worry is that the cow epidemic may have nothing to do with scrapie or the processing techniques used by renderers, said Dr. Richard F. Marsh, a veterinarian at the University of Wisconsin in Madison. There are reasons to believe that mad cow disease has already risen spontaneously in American cattle, he said. But it apparently has not jumped into the animal feed supply at this point.
The strongest evidence is an outbreak of mink encephalopathy (a disorder similar to mad cow disease) that occurred in 1985 in Stetsonville, Wis. The mink farmer did not feed commercial meal to his animals, Marsh said. Rather he fed them the meat from a downer cow, a cow that is down and cannot get up. It is possible that the cow had a spontaneous case of mad cow disease and passed it into mink, Marsh said.
Spontaneous cases of mad cow disease may well occur in one cow out of every million cows each year, said Dr. Joseph Gibbs, a leading expert on mad cow disease at the National Institute of Neurological Disorders and Stroke in Bethesda, Md. There are 150 million cows in this country, which means that each year 150 of them might develop mad cow disease -- all on their own, without any exposure to tainted feed.
Renderers pick up the carcasses of 100,000 downer cows every year and mix them in with other animals, Marsh said. Although the Agriculture Department tries to test downer cows for signs of mad cow disease, it can only sample a small percentage. Moreover, animals can be quite sick and not show signs of it before they are sent to slaughter, Marsh said. Thus, try as they might to avoid the problem, renderers could unknowingly introduce infected animals into animal feed and start an epidemic.
Deer and elk also have a spontaneous mad-cow-like disease, Gibbs said. If they die in the woods, the disease would not be transmitted. But if they are killed on the road, they are sent to zoos or greyhound tracks or, more often, go straight to the rendering plant to end up as cattle feed or pet food.