California has signed into law the toughest limits on antibiotics for livestock in the U.S.
The law bars the use of antibiotics that are important in human medicine to promote growth in animals raised for profit.
Under the new rules, a veterinarian must approve any use of those drugs to treat sick animals, and does not allow their use for preventing illness—a loophole that opponents say permits the use of antibiotics for fattening.
The regulations are more stringent than federal rules, which allow use of antibiotics to prevent disease.
California's new rules will not go into effect until January 1, 2018.
Online magazine Grist reported that industry opposition to the bill was weak, with farmers stating that they are already following U.S. Food and Drug recommendations to phase out non-medical use of antibiotics.
The U.S. Centers for Disease Control says at least two million people have been infected with bacteria resistant to antibiotics, and at least 23,000 people die annually as a result.