Hogs raised without antibiotics carry more pathogens

by Keith Nunes
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COLUMBUS, OHIO — The meat from hogs raised in a free range fashion and without antibiotics carries more pathogens and parasites than the meat from hogs fed low levels of antibiotics and raised in a conventional fashion, according to research conducted at The Ohio State University and published in Foodborne Pathogens and Disease.

A comparison of swine raised in antibiotic-free and conventional pork production settings revealed that pigs raised outdoors without antibiotics had higher rates of three food-borne pathogens than did pigs on conventional farms, which remain indoors and receive preventive doses of antimicrobial drugs.

"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 half of the pigs on antibiotic-free farms tested positive for Salmonella, compared with 39% of conventionally raised pigs infected with the bacterial pathogen. The presence of the Toxoplasma gondii parasite was detected in 6.8% of antibiotic-free pigs, compared with 1.1% 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.

Mr. Gebreyes would not 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."

The scientists tested pigs on farms in North Carolina, Ohio and Wisconsin. Of the total studied, 324 were raised in antibiotic-free systems and 292 lived on conventional farms. The researchers took blood samples to test for the presence of antibodies against bacterial and parasitic infections. The higher rates of infection on natural farms were consistent in all three geographic regions.

Of the three pathogens studied, the positive tests for the Trichinella roundworm surprised the researchers the most. Mr. Gebreyes said federal inspectors might expect to find one positive test for the parasite among more than 14,000 pigs, so the two positive tests among 600 pigs were significant.

The infection resulting from this parasite, trichinellosis, historically has been associated with undercooked pork, but in the recent past, the parasite has been associated mostly with wild mammals.

The nearly 7% of naturally raised pigs infected with Toxoplasma, while a relatively small number, still represented a significantly higher infection rate than that found in the conventional herds.

Mr. Gebreyes noted that routine antibiotic use does not fully prevent the occurrence of Salmonella bacteria even in conventional pig herds, as shown by the 39% of those pigs in this study that tested positive for the pathogen. By comparison, 54% of antibiotic-free pigs tested positive for Salmonella.

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