This One's an Udder Gas
Cows' indigestion problems lead to larger woes for humans
FRIDAY, May 25, 2001 (HealthDayNews) -- Too much starch, not enough fiber.
But it's Bessie the cow who's not eating properly these days. Too much grain in the diet of American cattle means all kinds of digestion problems for the animals. And that translates into increased reliance on antibiotics for the cattle -- and a heightened risk of bacterial contamination for humans, a new study says.
For millions of years, cows munched on fiber -- mainly grass and hay, according to James B. Russell, an Agricultural Research Service microbiologist in Ithaca, N.Y. Fifty years ago, at least 40 percent of cattle diet was still hay, grass and other forage. But today's farmers chiefly feed their cattle corn and other grains, finding that cheaper and more efficient for beef production.
The absence of fiber, Russell says, means cows have big digestive problems, so farmers feed them antibiotics. And that, he adds, endangers the usefulness of the drugs for humans. In addition, the cows' changed digestive environment creates a super-strong version of the dangerous Escherichia coli 0157:H7 bacteria, which kills dozens of Americans each year.
"Cattle didn't evolve as grain eaters, they evolved as grass-and-hay eaters. They need fiber in their digestive tract in order to keep it functioning well," Russell says. "Grain feeding can be bad for the cow."
In general, too much grain means the digestive system becomes more acidic, Russell says. That means cattle only produce about half the usual 50 to 100 liters of saliva each day, because saliva production is triggered by cud chewing, which, in turn, is prompted by eating fiber. And because starch ferments more rapidly than fiber, the result is a highly acidic mush in the cow's rumen, or large stomach.
Then, Russell says, because there is no protective mucous in the rumen, the acidity creates ulcers. The ulcers then launch the bacteria Fusobacterium necrophorum into the bloodstream. The bacteria travel to the liver, where they create thumb-sized abscesses. About 13 percent of cows' livers are discarded because they're contaminated by the abscesses, Russell says. But without the preventative antibiotics that cows are regularly fed with their chow, that number would rise to about 75 percent. In fact, preventing liver abscesses is probably the primary reason for feeding cattle antibiotics, he says.
The overuse of antibiotics in agriculture -- and in people -- is highly controversial, Russell says, because many bacteria are becoming resistant to antibiotics. Estimates vary, but somewhere between 17 million and 24 million pounds of antibiotics are fed to cattle, pigs and chickens each year in the United States. Humans consume about 3 million pounds of the drugs, too.
A more immediate danger to humans is the rise in E. coli 0157:H7 in cattle. The heightened acidity in the stomachs of cattle transforms the E. coli so it's resistant to acidity in human stomachs -- and that acidity protects us against harmful bacteria.
What that means, Russell says, is that if you eat beef contaminated with this transformed E. coli, your stomach can't kill it off.
E. coli contamination has been a rising concern in the United States in the last two decades. The Centers for Disease Control and Prevention estimates that about 73,000 Americans are sickened by, and 63 die from, contaminated beef each year.
Researchers are working to develop vaccines and bacteria and yeast that can fight harmful bacteria. And other, new forms of fiber may help improve cows' diets, Russell says. For instance, researchers are exploring the use of soybean hulls and leftover fiber from distillery grains.
And it looks as if a little may go a long way, Russell adds. One study showed that if you replace just five days of a cow's grain diet with fiber, you reverse the acid resistance that has built up over the previous 100-plus days.
"Given time and the right strategies, we could have a situation where grain-related disorders could be minimized," he says.
Russell's study appears in a recent issue of Science.
What To Do
For more on the latest outbreaks of E. coli, see these HealthDay stories.