Therefore a free choice accessibility to a trace mineral salt block or lick may be advantageous. During heavy and prolonged exercise, excessive amounts of sodium, chloride, potassium, calcium and magnesium are lost through extensive sweating. An additional supplement of these minerals given the day prior to competition may be helpful. Mix three parts of this mixture to one part of a calcium additive such as ground limestone to produce a good supplement. Two ounces of this supplement given with feed three or four times on the day prior to the competition may prove beneficial.
Commercial supplements are also available.
A diet of reasonable quality forage, hay and grain will usually supply all the necessary vitamins. The fat-soluble vitamins A, D and E are stored for long periods and shortages do not pop up overnight. Excessive supplementation of these can prove toxic. You should feed a moderate quality grass hay the night prior to the ride. During distance competition, horses get hungry, sometimes even ravenous.