I think part of it too, is that you have to stay, and the horses are controlled all night... The horses have that added stress of standing tied to the trailer... The endurnce folks aren't, are they? They can go home. Home food, home surroundings, home water, home turnout. And... No one would know if they colicked.
I think that could be a big factor in it too, never thought about it.
Thinking about it, if I remember correctly, when I have seen horses colic, it's usually been when the weather was very humid also.
Becky
Some rides are two day events, 50 each day, but most times, yes, the horse can go home and relax at the end of the day.