On talking about a horses diet he needs everything in a fair amount.
corn corn
Oats. Not good for ponies though as they get a real energy boost
howse answer riding level 3 - corn
energy food barley or oats
Corn usually provides the most energy for horses. also Rolled oats.
oats that's my guess
Corn.
Out of the common feed stuffs in the USA, corn has the highest Mcal value. The problem with corn is it is lower in protein, especially the necessary amino acid LYSINE. So It is important to add a protein supplement if feeding corn to horses. Always remember to do any dietary changes gradually to avoid colic and founder.
The more massive horse that is moving at the same speed will have greater kinetic energy. How do you define large and small? A small fat horse may have more mass than a large skinny horse.
You will need to feed the next highest amount available on the drop down menu. Or you can feed 13 pounds and then get the remainder by putting the horse in the meadow.
In comparison to its size, the horse is not the highest jumper in the world. Proportionally, it is the grasshopper.
Horses need a certain amount of minerals. Ask your vet which type of horse feed is best for your horse. here's the types of vitamins and minerals a horse needs: http://alpharmaequine.com/info-vitamin-mineral.html and here's more about horse's energy: http://alpharmaequine.com/info-vitamin-mineral.html