The work load of each horse needs to be determined to accurately gauge your horses energy requirements. A quick example would be that a horse in light work will need 1.25 times the energy of a sedentary horse and 1.5 times the energy for a horse in medium work. Generally horses in intense work will require twice as much energy as a horse not in work.
But this simple calculator takes all the guess work and math out and does it all for you and allows you to calculate the energy and nutrient requirements for your horse.