Prime Minister Stephen Harper and Calgary Mayor Naheed Nenshi donned their cowboy hats at the centennial Calgary Stampede kickoff Friday, which drew an estimated 400,000 people to one of the largest parades in Canada.

Calgarians and visitors from around the world watched the Stampede’s parade of floats, marching bands, horses, First Nations presenters and dancers wind its way through the city’s centre.

Billed as the “Greatest Outdoor Show on Earth,” the Stampede is celebrating its 100th anniversary this year. It’s one of the world’s largest rodeos, with a midway, stage shows, concerts, agricultural competitions and the famous chuck wagon races.

More than one million people are expected to attend Stampede events over 10 days.

Harper saluted the Stampede’s 100th opening as “a truly historic milestone and cause for great celebration.”

“I would like to thank all those involved in making the Stampede a success every year, and encourage everyone to take part in celebrating its 100th anniversary,” Harper said.

Nenshi posted messages on Twitter while riding his horse Garfield in the parade, CTV Calgary’s Lane Fraser reported.

“I’m on a horse. Tweeting,” Nenshi wrote, posting a photo of himself on the horse.

Other dignitaries who participated in the parade included Alberta Premier Alison Redford, who rode her horse Rowdy.

To mark the centennial, a 900-foot long zipline was set up across the parade grounds on which visitors could travel up to 60 kilometres an hour, starting at about 120 feet off the ground.

The Stampede has drawn more international attention this year due to both the milestone anniversary and Prince William and his wife Kate's visit to Calgary last summer.

Earlier Friday, Nenshi said he didn’t know if the Stampede’s founders in 1912, including visionary Guy Weadick, had any premonitions about how it would become ingrained in the “bloodstream and DNA” of every Calgarian a century later.

“So what’s unbelievably exciting about this year is there’s more of everything,” he said.

The Stampede also lives in the community, with citizens sharing in the celebrations through everything from neighbourhood pancake breakfasts to inviting friends to visit for the week, he said.

The event showcases what communities can do when they pull together and it’s a great example of Canada to show the world, he added.

Nenshi attended the Stampede as a young boy and said he has many fond memories from his childhood.

“I grew up here and I remember going with my parents to parade as a kid, I remember being on the midway as a teenager and trying to win big stuffed animals for various girls,” he said.

But his favourite Stampede memory isn’t from his childhood, but rather last year when he first rode a horse in the parade with a half million people watching, he said.

For many Albertans, the Stampede is a longstanding tradition.  Rose Recsky told CTV Calgary that her family has been attending the parade for 70 years.

“As young children, there were seven in the family, and my father used to pack us all in the car and take us to down to the parade,” she said.

But the parade also drew plenty of curious tourists, with some visitors coming from as far as Scotland and Taiwan.

The Stampede is expected to give the local economy a $12-million boost.

Stampede critics raise animal rights issues  

Nenshi brushed off complaints from animal rights groups that heavily criticized the Stampede for what they believe is mistreatment of calves and other animals.

The Vancouver Humane Society has used letter-writing campaigns to try getting sponsors to back away from rodeo events.

“Things evolve over time, they certainly do, and I think it’s worth noting that those activists are people who have largely never been to the Stampede and in fact, the Calgary Stampede works with the Calgary Humane Society extremely closely,” Nenshi said.

He said when people from places like the U.K. start writing him about calf-roping, he invites them to come see it in person and then determine if they have a problem with it.

“I think it’s great that people raise their issues, but I hope those discussion are informed discussions,” Nenshi said.

The rodeo is the heart of the Stampede, with prizes of more than $100,000 for bull riding, barrel racing, steer wrestling, tie-down roping, saddle bronc and bareback riding.

There’s about $1 million in prizes for the chuck wagon racers, who have their own separate competition.

The event is No. 5 on CNN’s top places to visit in 2012 on the American network’s list of “15 places to party sort of like a rock star”.

Wirth reports from The Canadian Press.