Horse digestive system — hindgut fermenter with a large colon
Overview of the equine digestive tract — hypsodont teeth, a small one-way stomach, no gallbladder, and a cecum and great colon that ferment fiber in a hindgut herbivore.
General educational reference only — not clinical or veterinary advice. Anatomy varies between individual animals; consult a licensed veterinarian for any health concern.
Teeth, saliva, and the stomach
Incisors crop grass, and high-crowned (hypsodont) cheek teeth grind it with a side-to-side jaw stroke, erupting continuously through life to offset wear. Saliva is produced mainly while chewing. The stomach is small relative to the horse's size, and the sphincter where the esophagus enters it is strong and obliquely angled, making flow effectively one-way; horses do not normally vomit.
Small intestine and liver
Beyond the stomach the long small intestine — duodenum, jejunum, and ileum — carries out enzymatic digestion and absorbs starch, protein, fat, and most minerals. The horse has no gallbladder: bile drains continuously from the liver into the duodenum, which suits a grazer that eats through much of the day rather than in a few large meals.
Cecum and great colon
Undigested fiber passes into the hindgut. The cecum is a large blind sac whose entrance and exit both lie near its top; from there ingesta moves through the great colon — right ventral, left ventral, left dorsal, and right dorsal portions joined by the sternal, pelvic, and diaphragmatic flexures — and then the transverse and small colon, where water is reclaimed and fecal balls form. Microbes throughout the cecum and colon ferment cellulose into volatile fatty acids, the horse's main energy source.
Sources
Veterinary anatomy and physiology texts; Merck Veterinary Manual (general reference)
