MADISON, Wis. (AP) -- State agriculture officials have quarantined 17 horses on 11 farms around Wisconsin after they were exposed to an equine venereal disease.

Most are mares bred to one of seven stallions in other states that have tested positive for the disease called contagious equine metritis. It can cause temporary infertility and spontaneous abortion in horses, but it's treatable and poses no threat to humans.

The quarantines are part of an investigation that involves at least 250 horses in 27 states. The probe began in mid-December when a quarter horse stallion on a Kentucky farm tested positive for the disease.

State officials say the general horse population is safe since the disease is transmitted only by breeding. But the U.S. Department of Agriculture is concerned the outbreak could threaten the country's $415 million horse, semen and embryo export business.