A mystery is unfolding at a wild horse inmate program facility in Cañon City.
Bureau of Land Management officials discovered 19 wild horses dead in a pen Monday.
Several other horses in the same pen appeared ill.
The BLM and veterinarians are working with state and federal animal health authorities to find out the cause of the illness.
Some of the horses that fell ill have been euthanized.
The facility has been quarantined while investigators try to determine what happened.