(Finish Line Horse) Apple-A-Day Horse Electrolyte is the original apple-flavored source of electrolytes and trace minerals for horses. Increased temperatures, humidity and workouts cause your horse to sweat more, requiring electrolyte replenishment. Apple-A-Day is free of sugar and fillers, so less is required. Feed 1/2 - 2 oz. daily, depending on temperature and conditions. Apple-A-Day may be mixed with feed or water. Powder.