As the battle wages on over the safety of feeding antibiotics to livestock for growth promotion, a new report reveals yet another source of unregulated antibiotics in American animal feed–spent ethanol grain.

The new report by advocacy group the Institute for Agriculture and Trade Policy suggests that a relatively new source of food for livestock may contain levels of penicillin, erythromycin and other antibiotics. Both of these are medically important drugs whose effectiveness in treating humans can be compromised by overuse in animal feed for non-sick animals.