Actually, keeping to the trotting gait is less stressful on a horse than galloping - trotting's 2-time beat means that as a horse's legs hit the ground, they do so in pairs, so halving the concussive effect compared to the 1-2-3-4 of the gallop.
Most of horses running in the Prix D'Amerique today ran wholly, or partially, unshod (has to be declared, like blinkers etc). They've got pretty hard and well-conformed hooves, as a rule. Great big fiddle heads as well, a lot of them, but you can't have everything I suppose.
I don't think there's any mental stress either, it's harder to persuade a recalcitrant or unhappy horse to do something he feels uncomfortable with when you're driving him, than when you're riding him.
Most of horses running in the Prix D'Amerique today ran wholly, or partially, unshod (has to be declared, like blinkers etc). They've got pretty hard and well-conformed hooves, as a rule. Great big fiddle heads as well, a lot of them, but you can't have everything I suppose.
I don't think there's any mental stress either, it's harder to persuade a recalcitrant or unhappy horse to do something he feels uncomfortable with when you're driving him, than when you're riding him.