I feed all but one of mine the same ration---They eat Southern States Performance textured and beet pulp mixed approximately 1/3 grain-2/3 beet pulp- add water and feed. The horses range in age from 2 yrs to 21 yrs. Grass hay and decent pasture.
The 28 yo gets Triple Crown Senior, pretty much all he will eat(but not free choice), and alfalfa hay, because he will not eat the grass hay. He is also supplemented with Accel Lifetime, and electrolytes. He goes out in the pasture, but I never see him graze, he just watches the other horses.