Getting the tendons cooled well after each class (or day if the classes are close together) will really help them feel more energised the next day - the IceVibe boots are great because they cool and massage the tendons!
I agree, electrolytes, water, even ice boots work very well.
Walk the horse between the classes. Give it electrolytes and a lot of water to drink. I recommend "Cavalor an energy boost" it's full of electrolytes and gives the horse new energy super quick!