Pigs Raised with Antibiotics Exhibit Lower Levels than “Organic” Pigs

A new study finds that although the demand for antibiotic-free pigs is increasing, pigs raised without antibiotics are more likely to have bacteria and parasites.

Pigs raised outdoors without antibiotics had higher rates of three food-borne pathogens than pigs on conventional farms, according to a comparison made between antibiotic-free and conventional methods.

“Animal-friendly, outdoor farms tend to have a higher occurrence of Salmonella, as well as higher rates of parasitic disease,” said lead study author Wondwossen Gebreyes, associate professor of veterinary preventive medicine at Ohio State University.

More than 50% of pigs reared on antibiotic-free farms tested positive for Salmonella, compared to 39 percent of conventionally raised pigs infected with the bacterial pathogen. The Toxoplasma gondii parasite was detected in 6.8 percent of antibiotic-free pigs compared to 1.1 percent of conventionally raised pigs. compared to 1.1 percent of conventionally raised pigs. And two naturally raised pigs of the total 616 sampled tested positive for Trichinella spiralis, a parasite considered virtually eradicated from conventional U.S. pork operations.

The U.S. Department of Agriculture recommends that consumers cook fresh pork to an internal temperature of 160 degrees Fahrenheit, since thorough cooking ensures that these infectious agents in food animals should pose no risk to human health. Gebreyes won’t recommend one type of pork production practice over another.

“We are just doing the science and showing the results,” he said. “Does having an antibiotic-free and animal-friendly environment cause the re-emergence of historically significant pathogens? I think that is an extremely important question for consumers, policymakers and researchers to consider.”

In an earlier published paper, Ian Philips, et al., wrote “The use of antibiotics in food animals selects for bacteria resistant to antibiotics used in humans, and these might spread via the food to humans and cause human infection, hence the banning of growth-promoters. The actual danger seems small, and there might be disadvantages to human and to animal health. The low dosages used for growth promotion are an unquantified hazard. Although some antibiotics are used both in animals and humans, most of the resistance problem in humans has arisen from human use. Resistance can be selected in food animals, and resistant bacteria can contaminate animal-derived food, but adequate cooking destroys them. How often they colonize the human gut, and transfer resistance genes is not known.”

It’s important to note that the study was funded by a grant from the National Pork Board. The results were published in a recent issue of the journal Foodborne Pathogens and Disease.


  • J. Journal of Antimicrobial Chemotherapy, Vol. 53, No. 1. (1 January 2004), pp. 28-52
  • Foodborne Pathogens and Disease, April 1, 2008, 5(2): 199-203.