There is mounting concern that use of antibiotics in livestock will contribute to antimicrobial-resistant pathogens, with repercussions for human and animal health. This report explores how limiting antibiotic use for livestock productivity-enhancement purposes may affect farmer practices and profits, as well as market prices and volumes. The animal agriculture sector is a major user of antibiotic drugs for disease treatment, disease control, disease prevention, and "production purposes" (such as growth promotion). Routine use of antibiotics-in humans or animals-can encourage antimicrobial resistance, which can lead to significant human and animal health risks. In 2013, the U.S. Food and Drug Administration (FDA) issued final guidance on voluntarily phasing out the use of medically important antibiotics (those important for therapeutic use in humans) for livestock production purposes.