Fireworks don't kill horses , the equine business (or hobby) certainly does. Here is the article.
I didn't want to start a topic about the "anti" fireworks people, nor mention names. But none the less, I do find it very frustrating and depressing that the sort of people who viciously campaign against fireworks on the grounds that they are "distressing to animals" are not objecting to stuff like this which goes on all the time and has been for many years in the horse owning world. It's not just the racing industry, although that does seem like the current target of investigation from the BBC, and fair play to them for that.
I actually support open and honest discussion about fireworks including potential distress, but struggle with people whose very grounds for banning fireworks is based on a double standard. That said the BBC themselves are hardly blameless as they screen the Grand National and promote it as a classic British Tradition. Maybe they should have a content warning along the lines of "The sporting event you are about to watch has a high chance of death for some of the animals involved."