Driver Layne Bremner says his heart sank when he realized his horse Duke was badly injured during the sixth heat of the Calgary Stampede chuckwagon races on Saturday night.
The animal suffered a broken right hind leg and the decision was made to euthanize it.
Bremner, who is a third-generation chuckwagon driver, says Duke loved to run and was one of his fastest lead horses.
"It's just like losing a family member, your heart just sinks right away. There's no words to describe the feeling that you have," he said.
Stampede officials said the injury appeared to be due to a collision with another wagon. Bremner received a $2,500 penalty as well as a five-second penalty for interference.
Duke was a 10-year-old thoroughbred who had a previous career as a racehorse before Bremner bought the animal three years ago.
The incident renewed criticism of the Stampede by animal rights activists.
"It's no surprise to us. We are angry because every year we say the only way to stop these deaths and injuries is to finally stop the chuckwagons and the rodeo," said Michael Alvarez-Toye with Calgary Animal Rights Effort.
The Stampede brought in new rules in 2011 aimed at making chuckwagon racing safer for the horses and competitors.
To reduce crowding, the number of outriders alongside each competing chuckwagon was decreased to two from four.
All horses are micro-chipped to track their health and racing record and are not allowed to race more than three days in a row.
And each horse is inspected by veterinarians when the animals arrive at the Stampede, and before and after every race.
Stampede lead veterinarian Greg Evans says the horses are very well maintained and cared for.
"In specific regard to chuckwagon racing compared to other sports, these horses are being cared for at an appropriate or above level ," he said.
"Year over year, they get better and better and better and I just think that shows a level of commitment that is impressive to anyone that is a horse owner or horse lover."
Bremner says fellow racers are quick to rally around when such accidents happen.
"They all come and talk to you and give you some moral support and help you along the way," he said.