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, Mr.
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, Mr.
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, Mr. 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.
Dr. 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 1980's, Dr. Detweiler said.
Yet another factor lay in the way greaves were processed
in conventional rendering plants, Mr. Anderson said. Until the early
1980's, 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, Mr. 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 so.
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 six-tenths of 1 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, Dr. 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, Dr. 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, Dr. 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, Dr. 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, Dr. 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, Dr. 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.
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