Researchers had previously noticed that kids raised on European farms have lower rates of asthma and allergies than other children (see Reuters Health story of June 1, 2010).

But the new findings help identify, at least in part, what specifically may protect some farm-raised youngsters against developing asthma or allergies.

"Nature can really teach us something here," said Dr. James Gern, a childhood allergy researcher at the University of Wisconsin School of Medicine in Madison, who wasn't involved in this research.

"People have grown up with animals and in outdoor environments for eons, and maybe our immune systems are tuned to developing normally in that sort of environment," he said.

Some earlier results suggested the large variety of bacteria and other microbes present on farms may play a role in staving off asthma, but not allergies. And researchers couldn't pinpoint the particular bugs that seemed to be responsible.

To investigate what else might explain the so-called "farm effect," the research team surveyed the parents of nearly 80,000 children who grew up in rural areas of Germany, Switzerland and Austria.

More than 9,600 of the kids were raised on a farm, 18,000 visited other people's farms and 52,000 never spent time on a farm.

The farms in these regions are family-run and often have a range of plants and animals, rather than a single crop or animal species as is common in many large industrial farms in the United States, said Sabina Illi, the lead researcher on the study from Munich University's Asthma and Allergy Research Group in Germany.

Her team found that 11 percent of the farm-raised kids had asthma, compared to about 16 percent of the kids who visited farms but weren't raised on one.

Among the children who never spent time on a farm, 18 percent had asthma.

Similarly for hay fever, about five percent of farm kids had the seasonal allergy, compared to close to 11 percent of kids who visited farms and 15 percent of kids who didn't spend time on a farm.

Wheezing and eczema were also less common in farm-raised kids, according to findings published in the Journal of Allergy and Clinical Immunology.

To parse out what it is about farms that may be tied to asthma and allergy protection, Illi's team asked a smaller group of parents more details about their kids' farm exposure.

The researchers found that having contact with cows and straw and drinking milk that came from the farm was linked with a 21 to 26 percent reduced risk of developing asthma compared to non-exposed kids.

Kids who had contact with cows and drank their milk also had a lower chance of getting hay fever.

Illi said it's possible the actual cows or straw might not be responsible for the reduced risk, but it could be that microbes in their vicinity, for example, have a protective effect.

This study and others suggest that "exposure to non-pathogenic microbes seems to be an important part of the education of the immune system," Gern told Reuters Health.

He said the link between straw and asthma could mean that exposure to certain plants is also beneficial for kids.

Although contact with cows and their milk and straw accounted for much of the lower asthma risk, about half of the farm effect remained unexplained, Illi told Reuters Health.

It would be valuable to find out what exactly is responsible for the lower asthma and allergy rates to ultimately develop some sort of intervention for kids who don't grow up on farms, according to Gern.

Still, Illi said there's currently not enough evidence to say bringing pregnant women or young children to a farm -- or exposing them to hay or raw milk -- could reduce later allergy or asthma risks.

SOURCE: bit.ly/JLQCG4 Journal of Allergy and Clinical Immunology, online April 23, 2012.

• A Permanent Economic Emergency