Antibiotic use on the nation's farms dwarfs the use of the life-saving drugs in human medicine and may play a much larger role than expected in promoting the spread of drug-resistant microbes, a new study of US agriculture shows.
The Union of Concerned Scientists, a Washington-based group often critical of US agricultural policy, reported Monday that 24.6 million pounds of antibiotics --- 70 percent of all such drugs produced --- are used each year on farms and feedlots to treat healthy animals, either to accelerate growth or to prevent outbreaks of disease.
"Feeding antibiotics to animals from birth to slaughter may modestly improve meat industry profits, but it puts everyone's health at risk," said Charles Benbrook, a former economist for the National Research Council and co-author of the report. "It is time to rethink how pigs, cattle and poultry are raised in the United States."
Because most major classes of antibiotics used in human disease also are used in livestock, the use of the drugs in feedlots and chicken farms inevitably increases the selective pressure that leads to the emergence and spread of resistant "superbugs" that, when passed on to humans through contaminated meat or other means, are more difficult, if not impossible, to control.
"Antibiotics are a precious resource and should be used in animals only when necessary," said Margaret Mellon, director of the Union of Concerned Scientists' food and environment program. She warned that indiscriminate use of antibiotics on farms could hasten "an era where untreatable infectious diseases are regrettably commonplace."
The group found that, even while health authorities have been urging humans to use antibiotics more judiciously, the livestock industry has been increasing its use of antibiotics to treat healthy animals.
Among the group's findings:
Most major antibiotics used to treat human disease --- including penicillin, erythromycin and tetracycline --- are used to treat healthy farm animals.
Approximately 13.5 million pounds of antibiotics that have been restricted for animal use in Europe are used on farms and feedlots in the United States.
Use of antibiotics to treat healthy animals has increased sharply since 1985, from about 16 million pounds a year to the current 24.6 million pounds.
Overall, the estimates --- about 10.5 million pounds of antibiotics used in the poultry industry, 10.3 million in hogs and 3.7 million pounds in cattle --- are sharply at odds with recent estimates by the livestock industry.
The Animal Health Institute, which represents livestock interests, challenged the accuracy of the latest estimates. The institute's own estimates, based on a survey of pharmaceutical manufacturers, suggest antibiotics accounted for only about 40 percent of the total antibiotics used in the United States.
The wide divergence between industry figures and those of its critics underscores what health officials say is a critical lack of public knowledge.
Pharmaceutical companies that make drugs for both human and animal use won't disclose their production figures, so no one really knows how, or where, most antibiotics are used. Even the total amount of antibiotics used for all purposes is disputed. Estimates range from 35 million pounds annually to about 50 million pounds.
"We simply don't know how most antibiotics are used in this country," said David Bell, coordinator of the Centers for Disease Control and Prevention's programs to control antimicrobial resistance. "It's a major void in our knowledge."
Although human usage can be tracked by prescriptions, the most extensive uses of antibiotics in animals, in which the drugs are added to feed and water, are virtually impossible to track. The CDC's action plan for combating antibiotic resistance calls for expanded efforts to monitor not only antibiotic use, but the spread of resistant microbes in animals and humans.
The Food and Drug Administration is considering regulations that would require drug companies to report the production and use of their products in agriculture, but the rules could take years to implement.
Mellon said coordinated action is needed by the FDA, CDC and US Department of Agriculture to develop "solid, reliable" information.