Intestinum tenue (Ileum et Jejunum)
The small intestine consists of the duodenum (approximately 1 m), jejunum (approximately 20 m, the longest segment), and ileum (approximately 0.3-0.5 m). The duodenum receives bile from the liver (horses have no gallbladder) and pancreatic enzymes. The jejunum is the primary site of nutrient absorption, with a massive mucosal surface area amplified by villi and plicae circulares. 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 cranial mesenteric artery supplies these segments and is the vessel most commonly affected by Strongylus vulgaris larval migration.
Small intestinal colic (strangulating or non-strangulating) is a common and potentially life-threatening emergency. Volvulus, intussusception, and entrapment are surgical emergencies. Diagnosis uses clinical examination, nasogastric reflux, and ultrasound. Prognosis depends on the specific lesion and time to treatment.
## Overview Epiploic foramen entrapment is a form of small-intestinal strangulation in which a loop of intestine passes through the epiploic foramen and becomes incarcerated. It causes acute, severe
## Overview A strangulating lipoma is a pedunculated fatty tumor that wraps around a loop of small intestine and cuts off its blood supply. It is common in horses older than 15 years and causes acute
## Overview Ileal impaction is obstruction of the ileum (the last part of the small intestine) by a solid mass of feed. It is more common in the southeastern United States and is strongly associated
## Overview Anterior enteritis, also called duodenitis-proximal jejunitis, is an inflammatory condition of the duodenum and proximal jejunum that produces functional ileus and massive fluid secretion
## Overview Small intestinal volvulus is twisting of the small intestine on its mesenteric axis, strangulating the blood supply. It causes severe acute colic, rapid deterioration, and reflux. It is a
## Overview Jejunal intussusception is telescoping of one segment of jejunum into an adjacent segment, causing obstruction and compromised blood supply. It is more common in young horses and may be a
## Overview A mesenteric abscess is a pocket of infection in the mesentery, often from Streptococcus equi (strangles) or, historically, migrating Strongylus larvae. It can cause recurrent colic, weig
## Overview Equine proliferative enteropathy is a bacterial infection of the small intestine caused by Lawsonia intracellularis. It primarily affects weanlings and yearlings in the fall and winter. T
Signs of colic (pawing, rolling, looking at the flank, lack of manure) need immediate veterinary attention. Early intervention improves outcomes.
## Overview Epiploic foramen entrapment is a form of small-intestinal strangulation in which a loop of intestine passes through the epiploic foramen and becomes incarcerated. It causes acute, severe colic with rapid deterioration and is a surgical emergency. Older horses and those that crib are at higher risk. ## Causes Anatomic passage of intestine through the foramen, facilitated by changes in intra-abdominal pressure or cribbing. ## Diagnosis Acute severe colic, nasogastric reflux, and findings at exploratory surgery. Ultrasound may show distended small intestine. ## Treatment Immediate surgical reduction and resection of compromised bowel if needed. Time is critical. ## Recovery and Prognosis Guarded. Survival depends on the length of strangulation and amount of bowel resected. ## Prevention None proven, though reducing cribbing may lower risk. Signs include: acute severe colic; nasogastric reflux; rapid deterioration; surgical emergency
## Overview A strangulating lipoma is a pedunculated fatty tumor that wraps around a loop of small intestine and cuts off its blood supply. It is common in horses older than 15 years and causes acute severe colic, reflux, and rapid heart rate. Surgery is the only treatment. ## Causes Mesenteric lipoma with a long stalk. ## Diagnosis Age, severe colic, reflux, and ultrasound. Confirmed at surgery. ## Treatment Emergency surgery to remove the lipoma and resect compromised intestine. ## Recovery and Prognosis Fair with early surgery. ## Prevention None. Signs include: acute severe colic; nasogastric reflux; rapid heart rate; typically horses older than 15 years
## Overview Ileal impaction is obstruction of the ileum (the last part of the small intestine) by a solid mass of feed. It is more common in the southeastern United States and is strongly associated with coastal Bermuda grass hay. Horses show moderate to severe colic that often responds only temporarily to pain medication, with small-intestinal distension on ultrasound and reduced manure output. ## Causes Ingestion of coastal Bermuda or poor-quality hay, sudden diet changes, dental disease, tapeworms, or reduced water intake. Narrowing of the ileum from any cause also predisposes. ## Diagnosis History (especially Bermuda hay), rectal examination, abdominal ultrasound showing distended small intestine, and response to treatment. Surgery confirms some cases. ## Treatment Medical management with fluids, analgesics, and lubricants succeeds in many horses. Surgery is required if pain is uncontrollable or the impaction does not resolve. ## Recovery and Prognosis Good with timely medical or surgical treatment. Delayed cases risk bowel damage. ## Prevention Gradual introduction of Bermuda hay, dental care, deworming, and adequate water. Signs include: moderate to severe colic; small-intestinal distension on ultrasound; decreased fecal output; temporary response to pain medication
## Overview Anterior enteritis, also called duodenitis-proximal jejunitis, is an inflammatory condition of the duodenum and proximal jejunum that produces functional ileus and massive fluid secretion into the small intestine. Large volumes of gastric reflux result, leading to dehydration, electrolyte imbalances, and endotoxemia. The disease is sporadic and appears more severe in the southeastern United States. Approximately 30 percent of cases develop laminitis as a complication. ## Causes The etiology remains unknown. Clostridium species and Salmonella have been isolated from reflux in some cases, but consistent causation has not been proven. Dietary factors, particularly high-concentrate feeding or abrupt diet changes, are suspected contributors in some horses. ## Diagnosis Acute onset of moderate to severe colic, fever, depression, and large volumes of orange-brown nasogastric reflux are characteristic. Rectal examination reveals distended small intestine. Differentiation from mechanical small-intestinal obstruction is critical; horses with anterior enteritis often become more comfortable after gastric decompression and may be febrile early, whereas obstructive cases usually worsen. ## Treatment Repeated nasogastric decompression, aggressive intravenous fluid therapy, anti-endotoxic and anti-inflammatory medication, and prokinetic agents form the mainstay of therapy. Broad-spectrum antibiotics are frequently administered. Surgery is reserved for cases that cannot be distinguished from strangulating obstruction or that fail to improve. ## Recovery and Prognosis Prognosis is guarded and depends largely on the duration of reflux and the development of laminitis or other complications. Horses whose reflux resolves within 48 to 72 hours generally have a better outlook. Laminitis markedly worsens prognosis. ## Prevention No specific prevention is established. Gradual dietary changes and avoidance of abrupt increases in concentrate may reduce risk in susceptible individuals. Signs include: acute colic; fever; depression; large volumes of nasogastric reflux; distended small intestine on rectal examination; tachycardia
## Overview Small intestinal volvulus is twisting of the small intestine on its mesenteric axis, strangulating the blood supply. It causes severe acute colic, rapid deterioration, and reflux. It is a surgical emergency. Delay results in extensive bowel death. ## Causes Unknown. Altered motility may predispose. ## Diagnosis Clinical signs and ultrasound showing distended small intestine. Confirmed at surgery. ## Treatment Immediate surgical correction and resection of non-viable intestine. ## Recovery and Prognosis Guarded. Depends on the length of compromised bowel and time to surgery. ## Prevention None. Signs include: severe acute colic; rapid deterioration; nasogastric reflux; surgical emergency
## Overview Jejunal intussusception is telescoping of one segment of jejunum into an adjacent segment, causing obstruction and compromised blood supply. It is more common in young horses and may be associated with parasites or enteritis. Ultrasound often shows a target-like lesion, and horses present with acute colic and reflux. ## Causes Altered motility from parasites, enteritis, or other factors allowing one segment to invaginate into another. ## Diagnosis Acute colic, nasogastric reflux, distended small intestine, and the characteristic target lesion on ultrasound. Confirmed at surgery. ## Treatment Surgical reduction or resection of the affected bowel. Time is critical to preserve intestinal viability. ## Recovery and Prognosis Fair if operated before irreversible damage. Delayed cases have higher mortality. ## Prevention Parasite control may reduce one risk factor. Signs include: acute colic; nasogastric reflux; distended small-intestinal loops; target-like lesion on ultrasound
## Overview A mesenteric abscess is a pocket of infection in the mesentery, often from Streptococcus equi (strangles) or, historically, migrating Strongylus larvae. It can cause recurrent colic, weight loss, and fever. Large abscesses may strangulate intestine, creating a surgical emergency. ## Causes Bacterial seeding, most often Streptococcus equi subspecies equi. ## Diagnosis Rectal palpation of a mass in some cases, ultrasound, and clinical signs of chronic colic or weight loss. Acute strangulation presents as severe colic. ## Treatment Long-term antibiotics for abscesses. Surgical resection or bypass if intestine is strangulated or obstructed. ## Recovery and Prognosis Guarded. Abscesses can be difficult to resolve completely. Strangulation worsens the outlook. ## Prevention Strangles biosecurity and, where relevant, parasite control. Signs include: recurrent colic; weight loss; intermittent fever; palpable abdominal mass in some cases; acute severe colic if strangulation occurs
## Overview Equine proliferative enteropathy is a bacterial infection of the small intestine caused by Lawsonia intracellularis. It primarily affects weanlings and yearlings in the fall and winter. The intestinal wall thickens, leading to protein loss. Signs include rapid weight loss, ventral edema, variable diarrhea, and a pot-bellied appearance with very low blood protein. ## Causes Lawsonia intracellularis infection. ## Diagnosis Clinical signs in a young horse, severe hypoproteinemia, ultrasound showing thickened small intestine, and fecal polymerase chain reaction or serology. ## Treatment Antibiotics (often a macrolide or tetracycline), plasma or synthetic colloids for severe protein loss, and supportive care. Most treated horses recover. ## Recovery and Prognosis Good with early treatment. Untreated severe cases can be fatal. ## Prevention Biosecurity and, in some settings, vaccination or monitoring of at-risk weanlings. Signs include: rapid weight loss; ventral edema; variable diarrhea; pot-bellied appearance; very low serum albumin and total protein
Small intestinal colic (strangulating or non-strangulating) is a common and potentially life-threatening emergency. Volvulus, intussusception, and entrapment are surgical emergencies. Diagnosis uses clinical examination, nasogastric reflux, and ultrasound. Prognosis depends on the specific lesion and time to treatment.
Signs of colic (pawing, rolling, looking at the flank, lack of manure) need immediate veterinary attention. Early intervention improves outcomes.
See the Small Intestine (Ileum/Jejunum) on our interactive 3D horse model. Open 3D Model