Joey is a seasoned endurance horse now and our crewing techniques seem to work well.
After a ride he gets 1 day off at pasture for each 10miles that he's completed. He is fed arnica and an arnica gel is applied to any sore / tight muscles. This is normally not necessary though.
He sometimes loses weight if we've had to travel a long way to the ride. So his feed is increased for a few days. And he also gets electrolytes a few days before and after each ride.
He has a thermatex rug which he wears while waiting for the vetting - it's important that he doesn't shiver.
To be honest, if the horse is fit enough for the work you ask, he wont need a lot extra compared to normal. x