Here's mud in your eye: Pigs raised without antibiotics in an effort to placate consumer fears over those chemicals carry more bacteria and parasites, which of course consumers fear in the wake of the tomato scare and beef, chicken and spinach contaminations of days gone by.

At least this is the conclusion of a study funded by the National Pork Board.

A comparison of pigs raised outdoors without antibiotics and swine reared in conventional pork production settings revealed that antibiotic-free creatures had higher rates of three food-borne pathogens compared with 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.

Antibiotics are fed to pigs to prevent them from getting sick in enclosed environments. But for the most part, the pigs could probably care less: The pathogens generally do not cause illness in the animals.

The scientists tested the blood of pigs on farms in North Carolina, Ohio and Wisconsin. Of the total studied, 324 were raised in antibiotic-free systems and 292 lived in indoor farms.

Nearly 7 percent of antibiotic-free pigs were infected with Toxoplasma gondii, compared to 1.1 percent of the conventional pigs. Most people with a functioning immune system can resist symptoms associated with infection by Toxoplasma, which is considered most risky for pregnant women and those with compromised immune systems.

Salmonella was common in both groups: 39 percent of the conventional pigs were infected with it and 54 percent of the no-antibiotic swine had it.

It seems this is a lose-lose situation.

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

Of the three pathogens studied, the positive tests for the Trichinella roundworm surprised researchers the most. 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 antibiotic-free pigs were significant.

The infection resulting from this parasite, trichinellosis, 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 diarrhea, 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.

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 university notes in a statement. The U.S. Department of Agriculture recommends that consumers cook fresh pork to an internal temperature of 160 degrees Fahrenheit.

The study is published in a recent issue of the journal Foodborne Pathogens and Disease.