Intestinum tenue
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 Duodenal ulceration is erosion of the duodenal mucosa, seen more often in foals than adults. Clinical signs include teeth grinding, colic after nursing, diarrhea, and poor growth. Severe
## Overview Duodenitis-proximal jejunitis (also called anterior enteritis or proximal enteritis) is an inflammatory condition of the proximal small intestine that causes marked fluid secretion, ileus
## Overview Duodenal stricture is narrowing of the duodenum, most often from scarring after ulceration (especially in foals) or from other inflammatory or neoplastic processes. It obstructs outflow f
## 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 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 A pedunculated lipoma is a benign fatty tumor on a stalk in the mesentery. In older horses the stalk can wrap around a loop of small intestine, strangulating it. This is one of the most c
## 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 Ascarid impaction is a small-intestinal obstruction caused by a large mass of Parascaris equorum (or Parascaris univalens) worms. It occurs almost exclusively in foals and weanlings, typi
Signs of colic (pawing, rolling, looking at the flank, lack of manure) need immediate veterinary attention. Early intervention improves outcomes.
## Overview Duodenal ulceration is erosion of the duodenal mucosa, seen more often in foals than adults. Clinical signs include teeth grinding, colic after nursing, diarrhea, and poor growth. Severe ulcers can perforate or heal with stricture formation. ## Causes Stress, illness, non-steroidal anti-inflammatory drug use, or other factors disrupting mucosal defense. The exact triggers in foals are multifactorial. ## Diagnosis Clinical signs plus gastroduodenoscopy or contrast studies. Response to anti-ulcer therapy is supportive. ## Treatment Acid suppression (omeprazole, histamine blockers), sucralfate, and management of underlying stress or illness. Severe cases may need intensive care. ## Recovery and Prognosis Good for uncomplicated ulcers with treatment. Perforation or subsequent stricture worsens the outlook. ## Prevention Minimizing stress in foals and judicious use of non-steroidal anti-inflammatory drugs. Signs include: teeth grinding in foals; colic after nursing; diarrhea; poor growth
## Overview Duodenitis-proximal jejunitis (also called anterior enteritis or proximal enteritis) is an inflammatory condition of the proximal small intestine that causes marked fluid secretion, ileus, and copious nasogastric reflux. Horses present with depression, mild to moderate colic, fever, and large volumes of reflux. The cause is often undetermined. ## Causes Unknown in most cases. Clostridium or Salmonella have been implicated in some horses but are not consistently isolated. ## Diagnosis Clinical findings of depression, fever, and voluminous reflux with relatively mild pain, plus ultrasound showing distended, hypomotile small intestine. Differentiation from surgical small-intestinal lesions is important. ## Treatment Repeated nasogastric decompression, intravenous fluids, anti-inflammatories, and supportive care. Surgery is avoided when the diagnosis is clear, as the intestine is usually viable. ## Recovery and Prognosis Fair with aggressive medical management. Laminitis is a significant complication (reported in up to 30 percent of cases). ## Prevention None specific. Signs include: massive nasogastric reflux; depression; fever; dehydration; mild to moderate colic; risk of laminitis
## Overview Duodenal stricture is narrowing of the duodenum, most often from scarring after ulceration (especially in foals) or from other inflammatory or neoplastic processes. It obstructs outflow from the stomach, producing recurrent colic after feeding, gastric reflux, and weight loss. ## Causes Healed duodenal ulcers, chronic inflammation, or rarely neoplasia or external compression. ## Diagnosis History of postprandial colic and reflux, plus contrast radiographs, ultrasound, or endoscopy/gastroscopy demonstrating delayed gastric emptying and narrowing. ## Treatment Surgical bypass (gastrojejunostomy) is often required for significant strictures. Medical management of concurrent ulcers is supportive. ## Recovery and Prognosis Guarded. Surgical cases can do well if performed before severe debilitation, but complications occur. ## Prevention Prompt treatment of duodenal ulceration in foals may reduce stricture formation. Signs include: recurrent colic after feeding; weight loss; gastric reflux; poor growth in foals
## 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 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 A pedunculated lipoma is a benign fatty tumor on a stalk in the mesentery. In older horses the stalk can wrap around a loop of small intestine, strangulating it. This is one of the most common causes of surgical small-intestinal colic in horses over 15 years. Signs are acute severe colic, reflux, and distended small intestine on ultrasound. Surgery is the only treatment. ## Causes Mesenteric lipoma with a long pedicle. ## Diagnosis Signalment (older horse), severe colic, reflux, and ultrasound. Confirmed at surgery. ## Treatment Surgical removal of the lipoma and resection of any compromised intestine. ## Recovery and Prognosis Fair. Short-term survival rates of roughly 50 to 80 percent are reported, better with early surgery. ## Prevention None. Signs include: acute severe colic; nasogastric reflux; tachycardia; absent gut sounds; distended small-intestinal loops on ultrasound
## 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 Ascarid impaction is a small-intestinal obstruction caused by a large mass of Parascaris equorum (or Parascaris univalens) worms. It occurs almost exclusively in foals and weanlings, typically around 5 months of age when worm burdens peak, and is often precipitated by administration of an effective anthelmintic that kills or paralyzes a heavy adult population. The resulting bolus of dead worms obstructs the jejunum or ileum, producing acute colic. ## Causes Heavy ascarid burdens develop in young horses before age-related immunity appears. Rapid kill by ivermectin, pyrantel, or other effective dewormers can create an obstructive mass. Impaction can also occur spontaneously in heavily parasitized foals. ## Diagnosis Acute colic in a recently dewormed foal or weanling is highly suggestive. Nasogastric reflux, distended small intestine on ultrasound or rectal examination (in larger foals), and sometimes worms in reflux or feces support the diagnosis. Exploratory surgery confirms the impaction. ## Treatment Medical management with fluids, analgesics, and lubricants is attempted in mild cases. Most clinically significant impactions require surgical enterotomy to remove the worm mass. Supportive care addresses dehydration and endotoxemia. ## Recovery and Prognosis Prognosis is fair with prompt surgical intervention in foals that are not yet in septic shock. Delayed treatment or intestinal rupture carries a poor prognosis. Survivors usually do well once the obstruction is relieved and parasite control is optimized. ## Prevention Strategic deworming that avoids sudden kill of massive burdens (for example, starting with fenbendazole in heavily infected foals) and environmental hygiene reduce risk. Fecal egg counts guide treatment in older foals. Signs include: acute colic in a foal or weanling; often shortly after deworming; nasogastric reflux; distended small intestine; depression
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.
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