Calgary Stampede officials say they are imposing the largest fine ever in connection with a chuckwagon collision that resulted in the death of a second horse at the world-renowned rodeo this year.

A horse belonging to driver Jim Knight was euthanized after a Stampede veterinarian discovered it had a fractured leg, officials said Friday.

In the first heat of Friday's chuckwagon races, Knight's rig collided with another belonging to Cliff Cunningham.

The event's safety commission announced Saturday that the collision was the result of Cunninghan's error. It also confirmed that the horse broke its leg in the crash. 

It had reviewed video of the crash and interviewed both Cunningham and Knight.

Cunningham was initially fined $2,500 for "wagon interference" during the race, but the amount was increased to $12,500.

One of Cunningham's own was euthanized a week ago, on the first night of the Stampede, after suffering a broken leg during a race.

The death of Cunningham's horse was considered due to a "catastrophic" injury and not the result of driver error, Stampede officials confirmed.

During a chuckwagon race, a driver leads a team of horses around a circuit.

After the death of six horses at the Stampede in 2010, rodeo officials have revamped the annual event's chuckwagon racing protocol.

All competing horses are now implanted with a microchip that tracks them during the races and at rest. Owners also have more stringent record keeping rules and are asked to submit a list of horses competing daily at 4 p.m.

In previous years, four outriders on horseback have accompanied each wagon as it thunders around the dirt track. This year the number of outriders is limited to two.

Still, several animal rights organizations have continued to denounce the Stampede's chuckwagon races believing that they are inherently cruel.

A week ago, when Cunningham's horse died, the Vancouver Humane Society (VHS) called upon the Calgary Stampede to suspend chuckwagon racing.

VHS spokesperson Peter Fricker argues that the most recent horse death is further evidence of how unsafe the races are.

"It's just too fundamentally dangerous for horses," he told CTV News Channel on Saturday. "It needs to be stopped immediately until it can be proved to the public that it can be made safe."

With files from The Canadian Press