Researchers from Ohio State University have revealed that pigs raised without antibiotics are more likely to carry bacteria and parasites that can lead to food borne illnesses.
During the study, the team pigs raised outdoors without antibiotics had higher rates of three food-borne pathogens than did pigs on conventional farms, which remain indoor, 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.
The researchers 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.
The presence of the Toxoplasma gondii parasite was detected in 6.8 percent of antibiotic-free pigs, compared to 1.1 percent of conventionally raised pigs.
Moreover, 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.
As long as pork is cooked thoroughly, the presence of these infectious agents in should pose no risk to human health.
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.
The infection resulting from Trichinella parasite has historically been associated with undercooked pork, but in the recent past, the parasite has been associated mostly with wild mammals.
People with this infection typically experience diarrhoea, vomiting, fatigue and fever first, followed by headaches, cough, and aching joints and muscle pains. The symptoms can last for months, and severe cases can be fatal, according to the Centers for Disease Control and Prevention.
"The advantage of using antibiotics is to prevent these infections from occurring. The disadvantage is it appears to create a favourable environment for strains of the bacteria that are resistant to antibiotics," he said.
"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.
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," he added.
The study is published in a recent issue of the journal Foodborne Pathogens and Disease.