A horse was put down Sunday night at the Calgary Stampede after it suffered a broken hind leg during the fifth heat of the chuckwagon races, officials confirmed Monday.

The horse was taken away in an ambulance and examined by a veterinarian, who determined it had a severely fractured cannon bone on its left hind leg, the Stampede said in a release.

The veterinarian determined the horse, part of Roger Moore's team, should be put down.

"It's not specific to chuckwagon racing, it's just a running injury," said Calgary Stampede spokesperson Kristina Barnes, adding the horse did not come into contact with anything on the track.

Barnes said the driver, Moore, is a man of few words, but you could see he was visibly upset by the death. She said the Stampede was respecting his privacy following the incident.

Rick Barnett often attends the Stampede and said incidents like this are difficult to watch.

"You know, those kinds of things do happen and it's unfortunate, but they do their best to make it as safe as possible."

One of the horses on Roger Moore's team, seen here getting in place for the 5th heat, suffered a broken leg during the race on Sunday night. (CBC)

After four horses died in the 2015 Rangeland Derby — as the chuckwagon races are officially called — the Stampede introduced new safety measures, including new wagon inspections that test the welds of the vehicles, a rebuilt inner rail of the track to prevent erosion during rainstorms and "minor tweaks" to the barrel placements to better align drivers as they come out of the opening figure-eight turns and reduce the chance of collisions.

More recently, the Stampede helped fund research with the University of Calgary, looking at the stress placed on chuckwagon poles during races.

Cause unclear

"Data is preliminary right now, it's going to progress, we'll have a report in to the Stampede by the end. But what we're finding now, it's not shocking, is that polls are bending during races, but nowhere near the point where they're going to break," said researcher Sam Pollock.

He hopes his work with help refine chuckwagon design and provide a template for consistency.

It's not yet clear what caused Sunday night's incident.

Chuckwagon horse dies at Calgary Stampede. More than 60 have died in race since 1986. <a href="https://t.co/kiA537T9e8">https://t.co/kiA537T9e8</a> —@VanHumane

The Vancouver Humane Society, a long-time critic of the Stampede's rodeo events, tweeted about Sunday's incident, saying 60 horses have died in the chuckwagon races since 1986.

The latest horse death prompted others on social media to call for a ban on the chuckwagon races, which have been a fixture of the Stampede's grandstand show since 1923.