Yes, the Stampede has had some unfortunate happenings this year. The bronc with the broken back from the empy buck is for sure a freak thing. I've only heard of it maybe once before and it was a horse in pasture that got a little exuberant while playing.
Unfortunately, heart attacks in racehorses are not uncommon. I work in racehorses and have only seen a handfull of horses go down with broken limbs. Heart attacks however, I have sadly seen quite a few times in racing and in training. There is usually a mixture of dehydration, heat, extreme exercise and stress that seems to cause it. I don't think I can remember an instance of a horse dying from a heart attack in winter? Keep in mind too that many of the chuck horses are retired or failed TB's. They tend to have much longer careers and race into older age than they would in flat racing. Lets not forget that there is $$ involved here as well, so don't count out drugs as a contributing factor. It's nice to think that there are no cheaters out there, but the fact is that some of those horses may have been doped. It stands to reason that it may be a contributing factor.
Now the horse that shattered a shoulder in the team penning was just a freak thing. Very sad. The rider was quite badly injored as well and from what I have heard is still in bad shape. They don't know if she will ever be the same.
Having lived near Calgary my whole life, I've never seen as much bad luck and loss of life as this year animal wise (last year, two wagon drivers lost their lives). I'm sure the terrible weather is playing a huge role in it - we've had nothing but severe storms and hail since the beginning of the week. Just today, there was a tornado warning for the south east of the city.
The conditions of the chuck wagon track were so bad on Tuesday that they actually cancelled the races for the first time in ninety-eight years!
But all in all, the Stampede is a very well run rodeo and event. I know a couple of people who perform in the rodeo, and one who worked in the chuck horse barn - they say that the conditions are very nice and the animals are well kept.