New evidence suggests that a class of antibiotics previously banned by the U.S. government for poultry production appears to remain in use, suggesting that growers are evading a ban on their use in treating chickens and turkeys.

The study, conducted by the Johns Hopkins Bloomberg School's Center for a Livable Future and Arizona State's Biodesign Institute, looked for drugs and other residues in feather meal, a common additive to chicken, swine, cattle and fish feed. The most important drugs found in the study were fluoroquinolones—broad spectrum antibiotics used to treat serious bacterial infections in people, particularly those infections that have become resistant to older antibiotic classes. The banned drugs were found in 8 of 12 samples of feather meal in a multi-state study. The findings were a surprise to scientists because fluoroquinolone use in U.S. poultry production was banned by the U.S. Food and Drug Administration in 2005.

This is the first time investigators have examined feather meal, a byproduct of poultry production made from poultry feathers, to determine what drugs poultry may have received prior to their slaughter and sale. Americans each year eat an average 100 pounds of poultry products, more than any other animal- or vegetable-derived protein source. Each year, the U.S. poultry industry raises 9 billion broiler chickens and 80 million turkeys, according to the U.S. Department of Agriculture. A large percentage of the fresh weight of these animals is inedible—an estimated 33 percent for chickens, for example—and is recycled for other uses, including feather meal.

Read more from Arizona State University Biodesign Institute.

To read about a federal push to limit antibiotic use in livestock, go to startribune.com.