U.S. federal drug regulators have restricted the use of a class of antibiotics known as cephalosporins for livestock, including cattle, pigs, chickens and turkeys, because they say such practices may have contributed to a growing threat in people of bacterial infections that are resistant to treatment.

The FDA initially proposed cephalosporin restrictions in 2008 but withdrew the rule due to opposition from veterinarians, farmers and drug companies. The current rule allows veterinarians to use the drugs to treat sick animals in some ways the FDA has not specifically approved, and wide discretion to treat small-scale-production animals like ducks and rabbits. The rule bans routine injections of cephalosporins into chicken eggs and large and lengthy dosing in cattle and swine.

“We believe this is an imperative step in preserving the effectiveness of this class of important antimicrobials that takes into account the need to protect the health of both humans and animals,” said Michael R. Taylor, deputy commissioner for foods at the FDA.