For related articles and more information, please visit OCA’s Factory Farming and Food Safety page, Farm Issues page, and our Health Issues page.

WASHINGTON-The vast majority of antibiotics given to livestock in the U.S. is mixed into the feed that animals eat, according to the Food and Drug Administration, raising concerns that mass dosing increases risks to human health.

Rep. Louise Slaughter (D., N.Y.), who made public the FDA revelation Friday, and others contend that the large-scale feeding of antibiotics to livestock speeds up antibiotic resistance in bacteria that can threaten human health. Livestock groups, such as the National Pork Producers Council, disagree.

The FDA itself has long been concerned that the widespread use of antibiotics on farms contributes to the quickening of the pace that the drugs become useless to humans.

When feed is used as a method of administering antibiotics, “some animals will eat too much, some animals won’t eat enough and some will eat just the right amount,” according to Gail Hansen, a farming specialist with the Pew Charitable Trusts’ Health Group. And sick animals will likely be the ones that don’t get enough because they tend not to eat as much as healthy animals, Ms. Hansen said.

There is no evidence, though, of “inconsistency” in the feeding of antibiotics fed to livestock, according to the pork group, which stressed that “feed mill mixing equipment is designed to add antibiotics in the proper amounts.”

The group also said there is no evidence that “the widespread use of antibiotics on healthy animals is contributing to the growth of bacteria resistant to the drugs we use to treat humans.”