I have personal expierence with horses tying up, mostly noticed with fillies and horses who recieve a lot of high protein feed. With my expierence the horses that tied up and the ones that would come back after strenous exercise and get so anxious and hot that their muscles and nerves tense up to the point where they can hardley walk. The best way to avoid that is the keep walking the horse after the exercise, don't let them stop, not even for a second and they can't just slowly walk, they need to keep an upbeat walk until they cool off.