What you mentioned actually happened, the horses were spooked by the loud military music, other horses and the cheering of the crowds. The most logical argument in these circumstances is to replace the horses and some horse lovers on other threads said that many exhibit sign of distress and have a metal bit in their mouth which is pulled tight to control them.
While beating a horse with a whip is considered animal abuse by those with common sense, it’s the other obligate tool of the racing industry, the bit, that delivers the most harmful blows of all.
What is the bit?
Designed to control horses by applying pressure in the mouth, the bit is a metal device held in place in a horse’s mouth via a bridle then attached to the reins or a lead. The bit is forced against areas of the horse’s mouth that are known to have an extremely high density of sensory receptors, via a rider’s pressure through the rein. The only possible experience for a horse of this pressure from the bit in its mouth is pain.