Drugged Cows

Antibiotics are feed for thought

Antibiotics like penicillin, streptomycin and tetracycline have revolutionized medicine, and they have been wonder drugs for agriculture as well. Today about two-thirds of our cattle and nearly all poultry, hogs and veal calves are raised on feed laced with the drugs. Animals consume almost 8 million Ibs. a year, nearly 40% of U.S. production. The antibiotics not only keep them healthy in their crowded pens but, for reasons not yet clear, also speed up growth on less feed. Now, after a quarter-century of largely uncritical acceptance, the practice is being sharply questioned. Reason: the drugs the animals consume may cause difficulties in man.

The trouble stems from the growing resistance of disease-causing microbes to antibiotics. By the 1970s, the trend had grown to alarming proportions. Penicillin, once a sure cure for most forms of venereal disease, in more and more cases turned out to be ineffective. When doctors tried alternative therapies, they discovered that some bacteria had resistance to several drugs.

These defenses were an example of extraordinary bacterial cunning. Along with their regular complement of DNA, of genes, the single-celled creatures are endowed with extra bits of genetic material called plasmids, which often provide a remarkable capability. The plasmids contain instructions enabling the microbe to produce enzymes that either destroy or immobilize the most powerful antibiotics. Floating freely within the cells, the plasmids can be transferred from one microbe to another. When this happens, a bacterium once vulnerable to a drug can acquire a resistance to it and, more important, pass that genetic defense on to its descendants.

Many scientists are afraid that the acquisition of such bacterial immunity is greatly hastened by adding antibiotics to animal feed. Most livestock already harbor large populations of drug-resistant bacteria, since the less hardy microbes are wiped out by the drugs. Opponents of the feed practice argue that even with relatively clean handling and packaging conditions, these bacteria could be transferred to meat and poultry products and eventually wind up in the human gastrointestinal tract. There they could pass on their defensive plasmids to resident bacteria in the gut. One strong piece of evidence: people who are often in contact with drug-containing animal feed or raw meat, like workers on farms or in slaughterhouses, have more drug-resistant bacteria in their intestines than do those in other occupations.

Since 1972 the Food and Drug Administration has been trying to follow the example of Britain and other European countries in limiting antibiotics in animal feeds. But a coalition of pharmaceutical manufacturers and farming interests has persuaded Congress to stay any action pending further studies.* This group contends that the real culprits are physicians who prescribe antibiotics indiscriminately for almost any ailment: colds, for instance, which are caused by viruses and are unaffected by antibiotics.

Another consideration, they add, is economic: limiting antibiotics in animal feed could substantially raise the cost of producing poultry and meat, in some instances by as much as 25%.

*The FDA has also been stymied in banning another substance given to animals to boost growth: the hormone DES (diethylstilbesterol), which is known to cause cancer in humans.

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