In 2010 the U.S. Food and Drug Administration (FDA) called for a strategy to phase out production use of medically important antimicrobials and bring the remaining therapeutic uses under the oversight of a veterinarian. The guidance document was issued December 2013. The formal implementation period began Jan 2017. It is now illegal to use medically important antibiotics (those used in human medicine) to promote growth or improve feed efficiency in farm animals. Any medically important antibiotics to be used in the feed or water to treat animal disease must be prescribed by a veterinarian. The Center for Veterinary Medicine (CVM) and the FDA have joint efforts in strategies to reduce the risk of antibiotic resistance.
FDA page on Antimicrobial Resistance: https://www.fda.gov/AnimalVeterinary/SafetyHealth/AntimicrobialResistance/default.htm
FDA page on About the Center for Veterinary Medicine (CVM): https://www.fda.gov/aboutfda/centersoffices/officeoffoods/cvm/default.htm