Salt is most commonly given by providing a trace mineralized salt block free choice. Salt is composed of sodium and chloride which are important in maintaining electrolyte and acid base balance. Over consumption of salt is usually not a problem if free choice, nonsaline water is available. The practice of provid-ing trace mineral salt will not only meet the horse's sodium and chloride requirements but will also meet its needs for other trace minerals. Copper and zinc have been implicated in metabolic bone disease.
Selenium is also a trace mineral required by the horse.
Most naturally occurring feedstuff will have enough sele-nium to meet the horse's needs. However, Kentucky is a selenium marginal state and as such most commercial feeds will contain selenium at .1 ppm. Therefore, do not top-dress it as a mineral supplement. Vitamins Vitamins A, D and E are the most common vitamins added to horse diets. Although B complex vitamins may not be commonly supplemented, including them in performance horse diets may be necessary.