Three horses died and a rider was seriously injured during a grim 24 hours at the Calgary Stampede.

CTV Calgary's Sage Pullen reported Monday evening that a horse on a chuckwagon team died of a heart attack Monday morning during a routine training run.

Later in the day a horse died during the novice saddle bronc event.

"We understand that the horse actually bucked its rider off and then continued bucking, it's called an empty buck, and bucked so hard that it actually broke its own back and had to be put down," Pullen told CTV News Channel.

On Sunday, a horse died instantly of a heart attack during the team cattle penning competition. The female rider sustained a traumatic head injury when she was pinned under the horse as it fell to the ground. The rider, identified as Amy Carver, is in intensive care in hospital, Pullen reported.

"The family says they are cautiously optimistic she will make a full recovery, but do say that it is still too early to tell," she said.

Animal deaths at the Stampede are not rare. Last year, three horses died during the chuckwagon events, while a steer died during the steer wresting event.

The Calgary Humane Society advocates banning events such as steer wrestling and calf roping from the Stampede, and helped bring about changes, such as untying a calf more quickly after it is roped. But Pullen said agency representatives are reserving judgment on the most recent incidents until they can speak with veterinarians about exactly what happened.

Stampede spokesperson Doug Fraser said the horse that broke its back, named Snider Mountain, belonged to the Stampede and was from its "Born to Buck" program. The program is based at a ranch in Hanna, Alta.

The other two horses were privately owned, Fraser said.

"To lose an animal regardless of the circumstance is difficult for the Calgary Stampede and the owners," he said.

With files from The Canadian Press