A recent University of Minne­sota study indicates distillers’ grains with soluble (DGS) do not contain significant antibiotic residues to be of concern to livestock producers.

Antibiotics are added during ethanol fermentation to control bacterial contamination. Bacteria compete with yeast during the ethanol fermentation process, which can lead to a reduction in ethanol yields and reduced-quality DGS. Virginiamycin and penicillin are designated by the U.S. Food and Drug Administration (FDA) as generally recognized as safe (GRAS) for use in ethanol and DGS production, though they are not the only antibiotics being used.

Livestock producers and their nutritionists have been wondering whether antibiotic residues might linger in the distiller’s co-products used in livestock diets and if they have any biological activity.

Seeking answers, Devan Paulus, a graduate student working with Jerry Shurson, swine nutritionist at the University of Minnesota, collected 20 distiller’s (wet) grains with solubles (DGS) samples and 20 distiller’s dried grains with solubles (DDGS) samples from various ethanol plants throughout the United States. The samples, collected quarterly for a year, were analyzed for virginiamycin, erythromycin, penicillin, tetracycline and tylosin residues. Further testing on E. coli and Listeria monocytogenes sentinel bacteria revealed whether the residues were active.

While all of the 117 samples tested to date contained antibiotic residues, only one sample was found to have an antibiotic residue active enough to inhibit E. coli growth. The residue concentrations in the distillers’ grains are much lower than minimum-approved Food & Drug Administration (FDA) feed levels for finishing swine. “Extremely low concentrations of penicillin (less than 0.2 ppm), erythromycin (less than 1 ppm), tetracycline (less than 0.008 ppm) and tylosin (less than 0.02 ppm) residues were detected in wet and dried distillers’ co-products,” Shurson explains. “Only two of the 117 samples contained low, but detectable, concentrations (0.5 and 0.6 ppm) of virginiamycin residues, but this level is well below the 1 ppm FDA GRAS approval level,” Shurson explains.

“It appears that there is minimal, if any, concern about residues having inhibitory properties when tested with the sentinel bacteria; thus, it is likely that the majority of antibiotic residues in distillers’ grains are inactivated during the ethanol fermentation process and subsequent derivation of distillers’ grains,” he adds. 

Lora Berg is a freelance writer from Lakeville, MN.