The US Food and Drug Administration reports that 13.1 million kilograms, or 80% of all antibiotics sold in the country go to livestock and poultry, raising further concerns about their excessive use being linked to a growing incidence of bacterial resistance to antibiotics.
http://civileats.com/2010/12/23/new-fda-numbers-reveal-food-animals-consume-lion%E2%80%99s-share-of-antibiotics-2/
http://www.organicauthority.com/blog/organic/twenty-nine-million-pounds-of-antibiotics-used-on-americas-livestock-fda/C6