The death toll continued to mount at the Calgary Stampede on Wednesday as a fifth horse died after the conclusion of the evening's chuckwagon races.

Stampede spokesman Doug Fraser said owner and driver Kurt Bensmiller noticed one of his horses was having difficulty after the race and asked a veterinarian to examine it.

"There was no apparent reason for the distress that this horse was under," said Fraser.

"The animal received minor treatment as of that time but passed away approximately 40 minutes later. The cause of death is unknown and Bensmiller has requested a post-mortem on the horse."

That could take several days.

So far this year, two horses have suffered fatal heart attacks, one was euthanized after a shoulder injury and a fourth broke its back from bucking too hard.

A rider is also in hospital suffering from a serious head injury after her horse fell on her.

A growing number of animal welfare organizations have taken the Stampede to task for what they see as cruelty masquerading as entertainment.

The protest spread this year to Britain, where an group called League Against Cruel Sports called on Ottawa to end "the immense cruelty" inherent in rodeos and suggested British travel agencies boycott the event by refusing to offer vacation packages to the Stampede.

In addition, more than 50 members of Parliament signed a motion in the British House of Commons asking the Canadian government to improve how animals are treated during the event.

Peter Ficker of the Vancouver Humane Society has called the deaths "depressingly predictable," noting more than 50 chuckwagon horses have died since 1986.

Many of those deaths have been in crashes or collisions, but not this year.

"They seem to be different and they're not being caused by accidents," said Fraser. "A lot of this is unfortunate because we just don't know why it's happening.

"The bottom line is that any death is a concern to the Calgary Stampede. We pride ourselves in animal care and we lead the industry in animal care, so when something like this happens it's concerning to all of us."

He noted that track conditions were good on Wednesday, though the chuckwagon races had been cancelled on Tuesday because of heavy rains turning the field into mud.

The Canadian Press