More than a dozen horses belonging to the California Highway Patrol (CHP) and other agencies are in quarantine while investigators work to determine what killed a CHP Mounted Patrol Unit horse earlier this week.

Lt. Rick Campbell, CHP spokesman, said that on May 5 CHP personnel discovered the 13-year-old Belgian Draft Horse mare dead in her stall. When a veterinary examination failed to immediately reveal the animal’s cause of death, the horse’s remains were transported to the California Animal Health and Food Safety Laboratory at the University of California, Davis (UC Davis), for necropsy and other testing, Campbell said. After the dead horse was discovered, 15 other horses belonging to the CHP, the Sacramento Police Department, and other agencies were quarantined, he said.

"We didn’t know what killed her, so we decided to lock (the other animals) down," Campbell said.

Campbell said the mare was a recent addition to the Mounted Police Unit, which is used in crowd control, special events, and public relations situations. The animal had just finished a 30-day trial period to determine her fitness for duty and had not yet been out on assignment