Dose imprecision and resistance: free-choice medicated feeds in industrial food animal production in the United States

Abstract

Background: Industrial food animal production employs many of the same antibiotics or classes of antibiotics that are used in human medicine. These drugs can be administered to food animals in the form of free-choice medicated feeds (FCMF), where animals choose how much feed to consume. Routine administration of these drugs to livestock selects for microorganisms that are resistant to medications critical to the treatment of clinical infections in humans.

Objectives: In this commentary, we discuss the history of medicated feeds, the nature of FCMF use with regard to dose delivery, and U.S. policies that address antimicrobial drug use in food animals.

Discussion: FCMF makes delivering a predictable, accurate, and intended dose difficult. Overdosing can lead to animal toxicity; underdosing or inconsistent dosing can result in a failure to resolve animal diseases and in the development of antimicrobial-resistant microorganisms.

Conclusions: The delivery of antibiotics to food animals for reasons other than the treatment of clinically diagnosed disease, especially via free-choice feeding methods, should be reconsidered.

Figure 1

Dose imprecision for food animals that consume FCMF and a pathway to antibiotic resistance. Overadministration leads to very high plasma or target tissue levels of antibiotic. Underadministration leads to levels of antibiotic that never reach minimum inhibitory concentrations (MICs). Intermittent dosing leads to levels of antibiotic that fluctuate and periodically dip below MICs for variable periods of time. ROS, reactive oxygen species. Dotted lines indicate positive feedback, potentially driving increased use of FCMF.