In : Recent

The horse evolved primarily as a grazing and browsing, hindgut fermenting herbivore, with a range of hydrolyzable and fermentable forage carbohydrates as its main source of energy. Pastures provide the primary habitat and nutrition for most horses, and the remaining stall-confined horses have approximately one-half of their nutrition supplied by conserved pasture, i.e., hay. Pasture composition varies with season and weather, especially in carbohydrate content [1]. Performance horse owners supplement a diet of pasture and hay with grain concentrates in order to meet energy demands of exercise. Most commercial horse feeds supply energy, protein and micronutrients that complement forages but are based on cereal grains containing abundant starch, which is alien to the nutritional heritage of the horse. When fed as two large meals a day, grain supplements may cause starch overload and set up a feeding-fasting cycle of metabolites and hormones. Common experience has been supported by epidemiological and experimental studies that associate grain concentrates with several digestive and metabolic disorders, including colic [2-4], laminitis [5], gastric ulcers [6], developmental orthopedic disease [7,8] and some forms of exertional rhabdomyolysis [9]. As hindgut fermenters, horses have an opportunity for small intestinal metabolism of simple sugars to glucose, which is more metabolically efficient than fermentation to volatile fatty acids, which is obligatory in the ruminant. Understanding the sites of carbohydrate digestion in the equine gastrointestinal tract is useful when considering energetic efficiency and performance, as well as digestive and metabolic disorders associated with carbohydrate sources rich in starch and sugar. This chapter will summarize carbohydrate metabolism, which encompasses the biochemical events associated with the breakdown of carbohydrate in food, from ingestion to energy production to excretion, with a focus on horses and comparisons with other species. Disorders associated with carbohydrate metabolism will be reviewed briefly, as well as methods for evaluating carbohydrates in horse feeds and assessment of glucose dynamics in horses.