Pulmonary hemorrhage is being blamed for the death of an outrider horse used in the GMC Rangeland Derby chuckwagon race during the final days of this year’s Calgary Stampede, which takes place in Alberta, Canada.

The Stampede’s GMC Rangeland Derby chuckwagon race pits four teams of horse-drawn wagons against each other in a series of elimination races over several days. Traditionally, each team consists of four wagon horses and four horses carrying outriders.

In recent years several horses have died in separate Calgary Stampede events, including the chuckwagon races. In 2011, Stampede management announced new rules intended to increase safety for both equine and human chuckwagon race participants, including veterinary inspections to determine whether horses are fit to compete in the race. Those deemed unfit are scratched from the event, while those deemed fit to compete undergo post-race veterinary inspections. The rules also mandate that no horse can run in the event more than three consecutive days, and all horses used in the chuckwagon races must rest at least one day in every four.

Calgary Stampede communications advisor Bonni Clark said that on July 10 a 10-year-old Thoroughbred named Huey collapsed and died just after Heat 4 of the chuckwagon race, during which he was used as an outrider horse. The incident took place after the race had been concluded and while the horse and rider were returning to the infield, Clark said.

Greg Evans, DVM, chief veterinarian for the Calgary Stampede chuckwagon race, said that a subsequent necropsy revealed that the horse had suffered a pulmonary hemorrhage.

“Basically a huge