Six horses have died at the Calgary Stampede — four of them from the chuckwagon races — of various causes since the event began a week ago. (CBC)

A chuckwagon horse that was put down Thursday night after falling during a race is the sixth to die at the Calgary Stampede this year.

Veterinarians euthanized the animal, which had been outriding for Grant Preece's rig in the sixth heat, after it fell in the corner of the track with a breakdown injury to its right front leg.

"The injury really is the most common catastrophic musculoskeletal injury among racing horses," said Stampede spokesman Doug Fraser. "That's not to be mistaken with a broken leg,"

Thursday's death brings to six the number of horses that have died at the Stampede in 2010:

• Two suffered apparent heart attacks.
• One was put down after it broke its back in the saddle bronc event.
• One was euthanized after it suffered a shoulder injury in the chuckwagon races.
• Another died of undetermined causes.

"To lose six horses in one year is very unusual. It's also very upsetting," Fraser said.

"Each of the six deaths is the result of distinct circumstances. And we want to point out that none of the deaths are the result of an on-track accident, human error or negligence."

'Always room for improvement'

While acknowledging that some of the deaths were unpreventable, Calgary Humane Society spokeswoman Desiree Arsenault said the Stampede still needs to make changes so that animals are less often put at risk of injury and death.

"In light of the stressful situations that some of the animals are in, in the events, I think there could be questions raised around physiological stress," Arsenault said.

"We need to take an in-depth look and always keep the animals' welfare at top of mind. And I think the Stampede does a pretty good job of doing that. That being said, there's always room for improvement."

Stampede wives defend rodeo

Alberta Tourism Minister Cindy Ady said on Friday that the Calgary Stampede is very responsible in the way it handles animals.

"If they were doing something they shouldn't be, I think that they would correct that and they make new rules all the time," she said.

"I think that you're seeing them act responsibly and it's the greatest show on Earth ... I think we have a very very good festival here and I think it will continue."

Meanwhile, the wives of some Stampede cowboys also spoke out on Friday, saying the rodeo doesn't deserve a bad reputation.

About 25 rodeo wives held up pink signs reading, "We love rodeo and animals" during the show.

Barb Robson, who organized the silent protest, said the wives had to stand up because it was unlikely the men would.

"Cowboys are very .… they don't say much and they don't necessarily want us to make a big deal, so it's really the wives who are taking more of a very quiet stance saying, 'We support rodeo and we don't want it to go away,'" she said.

Myra Takeda, whose husband is a tie-down roper, said some horses at the Stampede are worth as much as $100,000, so it wouldn't make sense to treat them poorly.

"All these animal rights people — you know, we're just as concerned as they are," she said.

"We are in the livestock business and we look after our animals. We feed and water them. If they weren't in tip-top condition like these athletes, they wouldn't be here competing."