After Wednesday's chuckwagon races a horse died of unknown causes, the fifth horse to die at this year's Calgary Stampede. (CBC)

A post-mortem has been ordered following the death of a chuckwagon horse at the Calgary Stampede Wednesday evening.

The horse from Kurt Bensmiller's team was examined by a veterinarian when it showed signs of stress after the races. It died about 40 minutes later.

Because the cause of death was not readily apparent, a post-mortem was set for Thursday, said Stampede spokesman Doug Fraser.

Four other horses have died in separate incidents at this year's event.

Three horses died on Monday: one from an apparent heart attack, another was put down after it broke its back during the saddle bronc event and a third was euthanized after it suffered a shoulder injury in the chuckwagon races.

On Sunday night, a horse had a suspected heart attack during the team cattle penning competition.

It fell on its rider, sending her to hospital with a serious head injury and a broken shoulder blade.