Regulators have reported finding antimicrobial residues in distillers grains, which are often used as animal feed.
The Food and Drug Administration reported in April 2012 that antimicrobial residues were found in four of 46 samples of distillers grains left over from ethanol production. Virginiamycin and penicillin were found in one sample, virginiamycin alone in two samples, and erythromycin in one sample. The FDA Center for Veterinary Medicine reported that it would take the information into consideration in developing a policy on antimicrobial residues in distillers products.
A 2009 FDA document on the project indicated that, at the time, about 98 percent of distillers grains sold were produced as fuel industry byproducts, and most of the rest resulted from beverage production. Of 2.65 million metric tons available for domestic use in the U.S. and Canada, about 90 percent was used in animal feed, with more than 80 percent fed to ruminants. Antimicrobials are used to combat bacterial contamination in ethanol fermentation.
In a 1977 proposal to withdraw some production uses of penicillins and tetracyclines, the FDA indicated that livestock owners had discovered antimicrobials increased growth among their animals a quarter-century earlier, when animals were fed grains left over as byproducts of the fermentation process used to create chlortetracycline.