Animal rights activists want chuckwagon races suspended at the Calgary Stampede after three horses died in a crash on Thursday night.

The accident happened in the fourth heat of the GMC Rangeland Derby when the left lead horse on Chad Harden's wagon collapsed in the back stretch.

The crash brought down the three other horses in the rig, and caused one of the two outriders and his horse to collide with the wagon.

A necropsy done Friday determined that the first horse died of a ruptured aortic aneurysm near the kidney, said Stampede spokesman Doug Fraser.

Harden and his outrider were not hurt in the crash.

The outrider horse and the right lead horse, both badly injured in the crash, were euthanized by veterinarians.

A third horse, on the right wheel, was also injured but was expected to survive.

Protests planned

Michael Alvarez-Toye of the Calgary Animal Rights Coalition wants an outright ban on rodeos.

"It always shocks and infuriates me … you'd think after 100 years they'd come to realize they cannot prevent deaths."

Christy Thompson of the Calgary Humane Society says the group does not agree with using animals for entertainment, but it will continue to work with the Stampede to ensure the welfare of the animals. (CBC)

Animal rights groups are planning protests to take place at the Stampede on Friday and Saturday. They are protesting what they describe as the cruel and unnecessary use of animals at the Stampede rodeo and chuckwagon events.

The groups say horses continue to die needlessly and an outright ban is the answer.

The Calgary Humane Society agrees, although it won't be out protesting, instead vowing to keep working with the Stampede to protect the health of the horses.

"Because there are no laws being broken we are monitoring what's going on down there, but certainly we would like to … make sure that with the inherent risks in these events that we are doing whatever we can to make these events as safe as possible for the animals," said Christy Thompson of the Calgary Humane Society.

She said they have peace officers down on the grounds every day ensuring the welfare of the animals.

Horses 'part of the family'

The president of the Alberta Professional Chuckwagon and Chariot Association says horses at the Stampede are treated well.

Shane Cartier is a good friend of the driver of the wagon involved in Thursday night's crash.

Chuckwagon driver Chad Harden speaks to reporters shortly after the crash Thursday night that led to the deaths of three of his horses. (CBC)

"They all drive horses because they love to drive horses and have horses in their life," he said. "If they didn't want to, they wouldn't be there, because it's way too much work. If you didn't like horses why would you feed 30 head of horses and take care of them and everything if you didn't love them."

Cartier saw the crash on TV and said it is always hard to watch.

"About as tough as it gets," he said. "He's a good friend and I know how much he cares for his horses, so it's a tough one to take. It was a terrible feeling for me watching it, and I know exactly what he is going through."

Cartier says rodeo and chuckwagon horses are like part of the family, echoing what the driver involved in the crash said in a emotional statement to the media.

"They're just like humans, they're our family," said Harden after the loss of his horses Thursday night. "It's just devastating for our whole family. It's hard to take."

Safety review wanted

Peter Fricker, a spokesman for the Vancouver Humane Society, says there should be a full safety review to find out why the accident happened.

Following the death of four chuckwagon horses in 2010, Stampede officials revamped the rules in a bid to make the sport safer.

A protest put on by animal rights groups was held near the Stampede Friday. (CBC)

The number of outriders for each chuckwagon was cut from four to two to make the track less congested.

Pre-race health checks by veterinarians and rest days for the horses were also made mandatory.

But Fricker said it's clear now those changes haven't made the sport safer.

"We think that there's something more fundamentally wrong with the race, and we're calling for a suspension of the chuckwagon races and a full and fundamental safety review to be conducted,” he said.

With files from The Canadian Press