Feed Additives and “Subtherapeutics” in Cattle

First, what is a “subtherapeutic”?The Food and Drug Administration Center for Veterinary Medicine (FDA/CVM) has a variety of approval classifications for antimicrobials in food animals. These include…1. Improvement in rate of gain2. Improvement in feed efficiency3. Control of disease4. Prevention of disease5. Treatment of diseaseThe first 2 would fall into the “subtherapeutic” category by all of the definitions I am aware of. This is regardless of whether these applications have an effect on disease or not. Control and prevention of disease are considered therapeutic uses by the FDA/CVM and the American Veterinary Medical Association. However, anti-food animal activist groups attempt to cast control and prevention uses into the “subtherapeutic” categories in an attempt to sway public opinion that these are irresponsible uses.Actually, I don’t know as I have ever heard the FDA/CVM use the term “subtherapeutic”, probably because it is a term designed more to incite public indignation than describe an activity of a drug. It is also typically used to imply that somehow these uses cause more of a problem with selection for resistant bacteria than uses for control, prevention, or treatment.Antimicrobials don’t cause mutations for resistance in bacteria. Antimicrobials select for bacteria in populations which have developed mutations, or have acquired genes for characteristics which allow them to resist the activity of antimicrobials at concentrations above that at which the general population of bacteria would be either growth-inhibited or killed.