In a study of 80 New England horse barn workers, 50 percent reported coughing, wheezing or other ailments in the past year. That's compared to just 15 percent from a control group of 74 people. More exposure to barn work also increased the rate of self-reported respiratory symptoms.

"It has long been known that lower respiratory illness is common in horses, and this is typically attributed to the amount of dust in barns," says lead study author Melissa Mazan, DVM, associate professor at Tufts.

"Our hope was to see whether this poor air quality affects horse owners, and it appears that it might," she says.

Respiratory distress may be as common among pig, dairy and chicken farmers, says Mazan. A 2001 study of European animal farmers found similar results.