The World Health Organization (WHO) published guidelines in November 2017 that state livestock industries should stop using antimicrobials to prevent disease or improve production in livestock. WHO also advocates reducing overall antimicrobial use in livestock, especially use of medically important drugs in human medicine. The guidelines contend that the potential human health benefits of lowering the prevalence of antimicrobial resistance in humans outweighs any potential harm of limiting antimicrobial use. (JAVMA news bulletin, December 2017)
    Most people in the United States would probably think this all sounds reasonable. However, in reality, these statements are confusing, make some assumptions that have little basis in science or facts and could lead to harm.
    First of all, there is a difference between using antimicrobials to prevent disease or improve production. In the United States using antimicrobials to improve production is no longer allowed. An example of preventing disease might be giving a pen of calves an antibiotic injection to prevent a pneumonia outbreak when moving into a new pen, or arriving on a new farm, for example, and this type of use is medically appropriate, and can significantly reduce animal suffering and disease. Lumping these two different types of use confuses the public and does not advance the cause of appropriate antimicrobial use.
    Second, while it is true that lowering the prevalence of antimicrobial resistance in humans could likely have human health benefits, it is not necessarily true that broadly limiting antimicrobial use in animals will reduce antimicrobial resistance in human disease. Antimicrobial resistance is a very complicated subject. Efforts to reduce resistance in humans need to be targeted toward specific actions. A recent summary of antimicrobial use in food animals for 2016 published by the Food and Drug Administration offers some insight why this is true.
    FDA classifies antimicrobials into two broad classes: medically important (for human medicine) and not medically important. FDA is concerned about developing drug resistance to medically important antimicrobials, not necessarily all antimicrobials. In 2016, medically important antimicrobials accounted for only 60 percent of all sales to the livestock industry. Blanket statements about antimicrobial use in livestock almost never consider this fact. Not medically important products are mostly ionophores (82 percent). While it is technically correct to call ionophores such as Bovatec and Rumensin antimicrobials, they really have nothing to do with antimicrobial resistance in humans, and including them in the discussion makes no sense.  
    Second, there is a difference between antimicrobial resistance to different antimicrobials. If we again look at the FDA summary, we find that 70 percent of all sales of medically important antimicrobials was for tetracyclines. Oxytetracycline, Tetracycline and Chlortetracycline are the specific compounds used in agriculture. Most of us will recognize oxytetracycline as the product in LA 200, and chlortetracycline as the product in Aureomycin crumbles. While it is important to minimize resistance to tetracyclines in humans, it is not accurate to blame resistance to newer antimicrobials that are critically important to human medicine, e.g. fluoroquinolones, or cephalosporins on tetracycline use in livestock. According to the FDA report, fluoroquinolones and cephalosporins each accounted for less than 1 percent of sales of medically important antibiotics in 2016. Again broad statements about overall antimicrobial use in livestock are not helpful and do not focus efforts toward solutions that actually could promote better human health. For example, some years ago Denmark introduced a requirement for mandatory reduction of antimicrobial use. Many dairy farmers stopped using dry cow antibiotic treatments as a result. While it is true that blanket dry cow therapy may not be necessary in well managed dairy herds, and implementing selective or no dry cow therapy could be considered responsible antimicrobial use, it is pretty clear that dry therapy represents a tiny fraction of antimicrobial use, and that its contribution to antimicrobial resistance to medically important human antimicrobials is probably miniscule.
    There are some other interesting statistics in the FDA report. First, total sales of approved antimicrobials decreased by 10 percent from 2015 to 2016. Total sales of medically important antimicrobials declined by 14 percent in 2016. The new Veterinary Feed Directive rule did not go into full effect until Jan. 1, 2017, so it is likely overall sales will decline even more in 2017. Second, the percentage of sales of medically important antimicrobials that were for improvement of production was 69 percent. This use will largely go away with the new VFD rule, so we can expect significant reductions in total sales for 2017.
    It would be helpful if discussions of antimicrobial use in livestock and its relation to antimicrobial resistance in humans would always start with understanding of facts about actual antimicrobial use in animals. Animal agriculture needs to be at the table of discussion regarding antimicrobial resistance, but opinions should be based on actual, specific use of antimicrobials rather than just citing overall use, or even overall use of medically important products.
    Jim Bennett is a dairy veterinarian at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.