Study: Pigs raised without antibiotics more likely to carry disease

While consumers are increasing demand for pork produced without antibiotics, more of the pigs raised in such conditions carry bacteria and parasites associated with food-borne illnesses, according to a new study from Ohio State University.

The study, conducted by Wondwossen Gebreyes, associate professor of veterinary preventive medicine at Ohio State University, found that in a comparison of swine raised in antibiotic-free and conventional pork production settings, 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," Gebreyes said.

Recently, the Pew Commission on Industrial Farm Animal Production released of a two-year investigation of the impact of intensive confinement practices in industrial farm animal production.

The commission is calling out for eventual phaseout and ban on antimicrobials for non-therapeutic use in food animals. 

The commission, concerned about the indiscriminate use of antibiotics in food animal production and the potential threat to public health, called for the following recommendations:

n Restrict the use of antimicrobials in food animal production to reduce the risk of antimicrobial resistance to medically important antibiotics.

n Clarify antimicrobial definitions to provide clear estimates of use and facilitate clear policies on antimicrobial use.

n Improve monitoring and reporting of antimicrobial use in food animal production in order to accurately assess the quantity and methods of antimicrobial use in animal agriculture.

n Improve monitoring and surveillance of antimicrobial resistance in the food supply, the environment, and animal and human populations in order to refine knowledge of antimicrobial resistance and its impacts on human health.

n Increase veterinary oversight of all antimicrobial use in food animal production, to prevent overuse and misuse of antimicrobials.

While the Pew Commission urges the banning of antibiotics in farm-raised animals, the Ohio State University Study found that more than half of the pigs on antibiotic-free farms tested positive for salmonella, compared to 39 percent of conventionally raised pigs infected with the bacterial pathogen.

According to the U.S. Department of Agriculture, as long as pork is cooked thoroughly according to federal guidelines, the presence of these infectious agents in food animals should pose no risk to human health. The USDA recommends that consumers cook fresh pork to an internal temperature of 160 degrees F. The pathogens generally do not cause illness in the animals.

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 percent of those pigs in this study that tested positive for the pathogen. By comparison, 54 percent of antibiotic-free pigs tested positive for salmonella.

On conventional farms, pigs remain indoors in ventilated barns and have free movement within pens. Antibiotics are added to their feed to promote growth and protect against infections, followed by a withdrawal period before slaughter to ensure the meat doesn't contain any antibiotic residue.

On antibiotic-free farms, pigs are reared in open fields with free access to soil and water. They are given antibiotics only for treatment against active infections, and once sick pigs are treated, they are separated from the herds and no longer marketed as naturally raised pork.

Salmonella is a common cause of food-borne illness, typically causing diarrhea, fever and abdominal cramps that resolve within a week and rarely require treatment in healthy people. More than 1 million people are infected by salmonella in the United States each year, according to the World Health Organization.

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

"The advantage of using antibiotics is to prevent these infections from occurring," Gebreyes said. "The disadvantage is it appears to create a favorable environment for strains of the bacteria that are resistant to antibiotics.

"On the other hand, when antibiotics are not used, the pigs tend to get less resistant bugs, but higher rates of the common bacteria of food safety concern," Gebreyes continued. "The prevalence of salmonella was significantly higher in the antibiotic-free herd than in the conventional herd. That could cause concern down the road about eating this product."

The researchers theorized that naturally raised pigs' exposure to moisture, vegetation and other animal species could contribute to their higher rates of pathogens.