The National Research Council (NRC) creates nutritional requirements for each species. With horses they use a calculator that factors in specific things for each individual horse in order to be certain the horse’s nutritional needs are being met.
As you could probably figure out, a race horse needs a different diet than a pasture ornament. A warm blood broodmare has different dietary needs than a miniature horse.
I found this horse feed calculator that is VERY similar on HorseMath.com Click this link and fill in the necessary info to determine what your horse(s) needs and to see if his current diet meets them.
Peace and good feed,