 Concerns have been raised about Smithfield's use of low doses of antibiotics to promote the pigs' growth, in addition to using antibiotics as part of a treatment regime.The concern was that the antibiotics were harmful to the animals and were contributing to the rise of antibiotic-resistant strains of bacteria.Smithfield said in 2005 that it would administer antibiotics only to animals who were sick themselves, or who were in close proximity to sick animals; however, in CAFOs all pigs are in close proximity to each other.