Antibiotics in Animal Feed

Antibiotics have been used increasingly over the last 50 years in animal feed for a couple of reasons. The antibiotics act as an anti-microbial agent as well as a growth-promoting agent. There are now a dozen antibiotics put into animal feed, including chlorotetracycline, procaine penicillin, oxytetracycline, tylosin, bacitracin, neomycin sulfate, streptomycin, erythromycin, linomycin, oleandromycin, virginamycin, and bambermycins (1). These twelve antibiotics are of microbial origin, and on top of these there are other chemically synthesized antimicrobial agents. The three main groups of chemically synthesized antibiotics are arsenical, nito-furan, and sulfa compounds.
Antibiotics are used in animal feed at a rate of 2-50 grams per ton for improved performance of animals. The rate increases to 50-200 grams per ton when specific diseases are being targeted. From 2009-2011, 72 percent of all United States sales of antimicrobials comprised of those routinely added to water or animal feed (2). There are major benefits from antibiotics, including increased efficiency and growth rate, treating clinically sick animals, and greatly reducing the incidence of infectious disease. There are a lot of risks with using this amount of antibiotics in feed, however. After being fed this food filled with antibiotics, the animals start to retain the strains of bacteria that are resistant to antibiotics (2). The resistant bacteria are then transmitted to other animals, and the resistant bacteria do well in the intestinal flora of the animals. The three main ways bacteria can exchange genetic material with other bacteria are transformation, conjugation, and transduction. All three of these ways of exchanging genetic material can change genomes and create new, more powerful strands of resistant bacteria. Humans can become infected with the bacteria too, mostly from interaction and contact with the infected animals' feces or by eating the infected meat.

1. "Effects of Antibiotics on Animal Feed." N.p., 1998. Web. 10 Oct. 2013.
2. Wallinga, D. "Do Antibiotics in Animal Feed Pose a Serious Risk to Human Health?"ScienceDaily. ScienceDaily, 11 July 2013. Web. 19 Oct. 2013.