Farm Animal Antibiotic Resistance and Stewardship

During the February 1st Animal Care Wednesday Webinar, we heard one of the leading experts discuss the challenging social concerns of antibiotic resistance. Michael Apley, Frick Professor of Clinical Sciences with the Kansas State University College of Veterinary Medicine, challenged listeners to better understand the difference between judicious use and stewardship of antibiotics by reviewing the many factors involved in epidemiology (study of incidence, distribution, and possible control of diseases).

Veterinary Feed Directive Considerations

A change in how antibiotics are authorized to be used in food animals is at the forefront of the antibiotic resistance discussion. Authorization by a veterinarian, through a veterinary feed directive (VFD) or a prescription, is how farmers and ranchers now have access to antibiotics used in feed or water, respectively. Veterinarians hold a huge responsibility and additionally are held accountable for how the products are used. Dr. Apley highlighted a “checklist” that veterinarians should go through for prescribing a VFD treatment for an animal.

  • Do I have a valid VCPR (Veterinarian-Client-Patient Relationship) to authorize this use?
  • Is there a reason (diagnosis) to use the product, or is it just habit?
  • Is it legal? (label directions allow its use in the species)
  • Is it proven effective?
  • Are there any residue issues to consider (in meat or milk)?
  • Are there any issues with antibiotic resistance?

Beyond this checklist, an additional overview discussed the U.S. uses and sales of the “Medically Important” and “Not Currently Medically Important” products. The tetracyclines (primarily oxytetracycline and chlortetracycline) make up approximately 70% of the total antibiotics sold for use in food animals. Approximately 95% of the antibiotics sold for food animal use in the United States are labeled for use in feed or water.

Public Perception

Another change around the antibiotic discussion is the influence social media and marketing campaigns have had on driving public perception. The drivers of change in food animal antimicrobial use were discussed in three categories 1) Legislation, 2) Regulation, and 3) “Retailation”. Examples of legislation included the California Senate Bill 27 that removed all over-the-counter sales of antibiotics and stated that no antibiotic could be used for prevention purposes, and the Animal Drug User Fee Act (ADUFA) that requires the sales of antibiotics to be reported. An example of regulation included the VFD. “Retailation” is described as retailers developing marketing claims on perceptions of antibiotic use in food animals to improve their market share. The likelihood of drastic changes to antibiotic use will be at the state level legislation or “retailation” by different companies making market claims.

Understanding Disease Outcomes


Antibiotic stewardship starts with understanding how antibiotics fit into treating infectious disease. A disease outcome is determined by the interaction of the Disease, the Animal, and the Therapy. In Figure 1, the yellow line on the left shows the linkage between the regimen of the antibiotic to the susceptibility of the pathogen causing the disease. All of the factors within the red-shaded area represent judicious use of antibiotics. All of the factors within the yellow-shaded area represent stewardship of antibiotics; this is where we do everything possible to not even need to use antibiotics on an animal. Dr. Apley challenged that the core question is not to justify the use of antibiotics because they make a clinical outcome difference in a specific disease, the core question is why do we have to use antibiotics to make a difference.

Human Medicine


In addition to discussing the factors that influence the outcome of a disease and how antibiotics are used, the relationship between antibiotic use in food animals and antibiotic resistance in human medicine was also explored. Resistance can be described as a person not receiving the correct antibiotic the first time to treat the bacteria. However, with some antibiotic resistant microorganisms there may be a very limited number of antibiotics the pathogen is susceptible to. It is also important to understand that some bacteria can be transferred between people and animals and result in an illness in both (zoonotic disease), while some bacteria only cause illnesses in one or the other. We all need to be aware that food animals do have a relationship to the potential of antibiotic resistance through the food chain, but the direct relationship of food animal antibiotic use to antibiotic resistance within human medicine is a very small piece of the bigger picture. Nevertheless, veterinarians and animal caregivers assume their responsibilities to care for the animals to the best of their abilities through the stewardship of and judicious use of antibiotics.