Virginiamycin is a streptogramin antibiotic similar to pristinamycin and quinupristin/dalfopristin. It is a combination of pristinamycin IIA (virginiamycin M1) and virginiamycin S1. Virginiamycin is used in the fuel ethanol industry to prevent microbial contamination. It is also used in agriculture, specifically in livestock, to accelerate the growth of the animals and to prevent and treat infections.  Antibiotics also save as much as 30 percent in feed costs among young swine, although the savings fade as pigs get older, according to a new USDA study.