February 15, 2010

Too Much or Too Little: The Hazards of Mixing Antibiotics in the Feed Given to Food Animals

Center for a Livable Future

Center for a Livable Future

How food animals are given medication can be very different from how you take medication.  While humans are prescribed antibiotics at specific dosages in pills or injections, food animals are often given antibiotics mixed in their feed and freely choose how much to consume.  These free-choice medicated feeds (FCMF) make it difficult to deliver an intended or predictable dose of antibiotics to food animals. The result can be disastrous; under-administration of antibiotics leads to unresolved infections and contributes to the development of antimicrobial resistance, while over-administration can cause animal toxicity and increase drug residues in meat and milk.

A new commentary in Environmental Health Perspectives, lead authored by Dave Love, PhD, CLF’s project director of Aquaculture and Environmental Public Health, sheds light on the practice of administering antibiotics in FCMF. The Food and Drug Administration has approved 685 drugs for medicated feed, many of which are consumed on a free-choice basis, according to Dr. Love, who looked into the practice with co-authors Meghan Davis, DVM, MPH a CLF Pre-doctoral Fellow and Sommer Scholar, Anna Bassett, Lead Technical Auditor and Andrew Gunther, Program Director of Animal Welfare Approved, an organization which audits and certifies family farms on the basis of humane animal husbandry, and senior author Keeve Nachman, PhD, MHS, Director of CLF’s Farming for the Future Program.

Their commentary, “Dose Imprecision and Resistance: Free-Choice Medicated Feeds in Industrial Food Animal Production in the United States,” discusses the history of medicated feed, the nature of FCMF use, and its role in development of and selection for antimicrobial-resistant microorganisms. The commentary also discusses legislative efforts to address antimicrobial use in food animal production.

While data on antibiotic use in food animal production are not made available to the public, it has been estimated that 13 million kg of antibiotics are administered to food animals annually.  The use of these drugs has been shown to select for antibiotic-resistant bacteria at and around food animal production sites, which can become available for exposures in surrounding communities, potentially leading to infections that respond poorly to antibiotic therapy.  The fraction of resistant infections attributable to food animals has yet to be determined, although it is though to be considerable.  “The increasing number of antimicrobial-resistant infections and their costs in the US, estimated to be $16.6 to $26 billion per year in 2009 (Roberts et al., 2009), are of growing concern,” says the research team.  Antibiotic-resistant infections in humans “have been associated with the production of swine, poultry and dairy cattle in Europe (Broens et al. 2008), and the potential for similar exposure pathways exists in the US” determined the research team.

The authors note increasing concerns surrounding the uncontrolled use of antibiotics in food animal production. “Delivering antibiotics to food animals for reasons other than treatment of clinically-diagnosed disease, especially via free-choice feeding methods, poses an unnecessary public health risk,” they conclude, urging replacement of FCMF with improved hygiene and animal husbandry practices, and when absolutely necessary, enhanced veterinary supervision of antimicrobial administration.

The final commentary will be published in an upcoming print edition of Environmental Health Perspectives.

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