Feed-grade corn oil is easy to add to a grain mix. Some commercial grain mixes contain added fat. Rice bran is a source of added fat too. Another advantage of fat in summer rations, in addition to less feed being eaten, is the fact that fat seems to aid thermoregulation or allows horses to more easily get rid of the extra body heat produced by exercise. Often owners mistakenly feed too much protein.
Protein needs, as well as that of other nutrients, is related to energy intake.
As energy needs increase, so does that of other nutrients. There is probably a small increase in protein required for more intense performance. However, this need for extra protein is easily met by the increased amount of feed fed to meet the energy needs of the horse. For example, a horse is fed three pounds of a 10 percent protein feed. This is increased to six pounds to meet the added energy needs due to extra performance.