Wisconsin agricultural officials have quarantined 17 horses on 11 farms around the state after they were exposed to a contagious venereal disease.

State officials say most are mares bred to one of seven stallions that have tested positive for contagious equine metritis in other states.

The quarantines are part of an investigation that involves at least 250 horses in 27 states, including quarantines of at least one mare in Montana and farms in two Virginia counties.

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. The U.S. Department of Agriculture, however, fears the outbreak could threaten the country's $415 million horse, semen and embryo export business.