Your horse’s physical activity falls into two general categories. Anaerobic exercise (characterized by short bursts of maximum effort—think cow horse, barrel racer) is primarily fueled by glycogen, a polysaccharide composed of sugars and stored in muscle fibers. Soluble carbohydrates from the diet provide the building blocks for glycogen. Aerobic exercise (characterized by low- to moderate-intensity activity lasting from several minutes to several hours—think reiner, trail horse) is primarily fueled by fat, a slow-burning fuel. No performance activity is either all anaerobic or all aerobic, but fueling your horse with a mind to the dietary energy source from which he draws the most fuel can boost his performance (purinamills.com/horse-feed).