Intestinum tenue
The small intestine consists of the duodenum (~1 m), jejunum (~20 m, the longest segment), and ileum (~0.3 m). The duodenum receives bile from the liver (no gallbladder in horses) and pancreatic enzymes. The jejunum is the primary site of nutrient absorption, with a massive mucosal surface area amplified by villi. The ileum connects to the cecum at the ileocecal valve and is the site of vitamin B12 absorption. The entire small intestine is suspended by a long mesentery, which provides mobility but creates risk for volvulus, intussusception, and entrapment.
The equine small intestine is approximately 20-27 meters long with a capacity of 40-70 liters. It is the primary site of enzymatic digestion and absorption of proteins, fats, simple carbohydrates, vitamins, and minerals. Transit time through the small intestine is rapid (1-2 hours). Transabdominal ultrasound (wall thickness >3mm is abnormal; normal diameter <3-5 cm) and nasogastric intubation are essential diagnostics. Surgical colic involving the small intestine generally has a more guarded prognosis than large colon issues.
Ulcers in the duodenal mucosa, more common in foals.
See Anterior Enteritis above.
Narrowing of the duodenum, often from healed ulcers.
Small intestine herniates through the epiploic foramen and becomes strangulated.
Inflammation of the proximal small intestine causing massive fluid sequestration.
A fatty tumor on a stalk wraps around a loop of small intestine, causing strangulating obstruction. Most common in older horses (>15 years) and ponies.
Obstruction of the ileum, often from coastal Bermuda grass hay.
Obstruction of the small intestine by a bolus of dead or dying Parascaris equorum following anthelmintic treatment in young horses (3-12 months). Mass die-off causes impaction.
Ulcers in the duodenal mucosa, more common in foals. Signs include: Teeth grinding (bruxism) in foals; colic after nursing; diarrhea; poor growth
See Anterior Enteritis above. Signs include: Massive nasogastric reflux; depression; fever; dehydration
Narrowing of the duodenum, often from healed ulcers. Signs include: Recurrent colic after feeding; weight loss; gastric reflux
Small intestine herniates through the epiploic foramen and becomes strangulated. Signs include: Acute severe colic; nasogastric reflux; rapid deterioration; surgical emergency
Inflammation of the proximal small intestine causing massive fluid sequestration. Signs include: Depression; large volumes of nasogastric reflux; dehydration; laminitis risk; fever
A fatty tumor on a stalk wraps around a loop of small intestine, causing strangulating obstruction. Most common in older horses (>15 years) and ponies. Signs include: Acute severe colic; nasogastric reflux; tachycardia; absence of borborygmi; multiple distended small intestinal loops on ultrasound
Obstruction of the ileum, often from coastal Bermuda grass hay. Signs include: Moderate to severe colic; small intestinal distension on ultrasound; decreased fecal output
Obstruction of the small intestine by a bolus of dead or dying Parascaris equorum following anthelmintic treatment in young horses (3-12 months). Mass die-off causes impaction. Signs include: Acute colic in a young horse within 24-48 hours of deworming; nasogastric reflux; small intestinal distension; surgical cases may yield hundreds of worms
The equine small intestine is approximately 20-27 meters long with a capacity of 40-70 liters. It is the primary site of enzymatic digestion and absorption of proteins, fats, simple carbohydrates, vitamins, and minerals. Transit time through the small intestine is rapid (1-2 hours). Transabdominal ultrasound (wall thickness >3mm is abnormal; normal diameter <3-5 cm) and nasogastric intubation are essential diagnostics. Surgical colic involving the small intestine generally has a more guarded prognosis than large colon issues.
See the Small Intestine on our interactive 3D horse model. Open 3D Model