The horse was hurt when Rae Croteau Jr.'s unit, seen leading the pack, bumped into Reg Johnstone's rig, whose horses can be seen at the far right. (CBC)

A horse injured during a chuckwagon race on Wednesday night at the Calgary Stampede had to be euthanized.

In the seventh of the night's nine heats, Rae Croteau Jr.'s unit bumped into Reg Johnstone's rig, said Stampede spokesman Doug Fraser.

It wasn't until the race ended that a veterinarian discovered serious injuries to the horse's left front leg, he said.

"After the race ends, there's a practice in the case of collisions, a veterinarian was called in to check the horses involved. The vet determined one of Johnstone's horses had sustained a significant injury and it was euthanized to avoid further suffering," said Fraser.

Driver Rae Croteau Jr. was penalized 10 seconds and fined $2,500 in the collision. (CBC)

Judges penalized Croteau 10 seconds and fined the driver from Bonnyville, Alta., $2,500 for interference. Under rules introduced at this year's competition, he will also have to pay Johnstone $10,000 for the loss of the horse.

This is the first animal fatality at the Stampede this year.

Last summer, a chuckwagon crash killed three horses and injured a driver. In its wake, a safety review committee recommended tougher penalties for aggressive drivers, as well as a code of conduct and a unified set of rules for chuckwagon racing.