Antibiotics, such as penicillin and tetracyclines are widely used in animal feed to promote growth in chickens, pigs, and cattle. 80% of the antibiotics used in the U.S. are given to livestock to promote growth and stave off potential infections. The amount of meat which has been treated with antibiotics has grown from 17.8 million pounds per year in 1999 to 29.8 million pounds in 2009.
