The Union of Concerned Scientists estimates that 70 percent of the antibiotics used in this country are fed to farm animals. These animals do not receive these drugs the way humans do — as discrete short-term doses. Agricultural antibiotics are a regular feed supplement intended to increase growth and lessen the chance of infection in crowded, industrial farms.

These practices are putting both humans and animals increasingly at risk. In an environment where antibiotics are omnipresent, as they are in industrial agriculture, antibiotic-resistant strains of diseases quickly develop, reducing the effectiveness of common drugs like penicillin and tetracycline.

Despite that danger, the Food and Drug Administration had been reluctant to restrict routine agricultural use of antibiotics. The F.D.A.’s principal deputy commissioner, Dr. Joshua Sharfstein, signaled a welcome change in direction recently, testifying on behalf of a new bill, the Preservation of Antibiotics for Medical Treatment Act. It would allow veterinarians to prescribe antibiotics to treat individual animals or prevent disease, but it would sharply restrict the routine feeding of antibiotics to farm animals — the practice most closely associated with the development of drug-resistant pathogens.

The legislation is drawing strong opposition from the farm lobby since the restrictions would make it much harder for industrial farms to crowd thousands of animals together in confined, inhumane and unhealthy quarters. But the current practice is dangerously self-defeating: treating more and more animals with less and less effective drugs and in turn creating resistant strains of disease that persist in the soil and water. Congress should stop this now before an entire class of drugs becomes useless.