Intestinum
The equine intestinal tract is approximately 30 meters long and is specialized for hindgut fermentation of fibrous feed. The wall of any intestinal segment has four layers: mucosa (absorption and barrier function), submucosa (vessels and nerves), muscularis (peristalsis), and serosa (outer covering). Different segments (small intestine, cecum, large colon, small colon) have distinct roles in digestion, fermentation, and water absorption. Health of the mucosa and the microbiome is essential for normal function.
Colic, enteritis, displacement, or impaction can involve any segment. Wall thickness can be measured with abdominal ultrasound. Malabsorption can be investigated with glucose or D-xylose absorption tests or biopsy in selected cases.
## Overview Small colon impaction is obstruction of the descending (small) colon by dry ingesta. Horses show mild to moderate colic, straining to defecate, and reduced or absent manure. It is less co
## Overview Small colon volvulus is rotation of the small colon that strangulates its blood supply. It causes severe colic and absent fecal output and is a surgical emergency. Delay leads to irrevers
## Overview A fecalith is a hard, stone-like mass of inspissated feces that can obstruct the intestine, most often the small colon. It causes recurrent or progressive colic and straining. Miniature h
## Overview Meconium impaction is retention of the foal’s first feces. Meconium is sticky material composed of intestinal secretions and swallowed amniotic fluid. Most foals pass it within 12 hours.
## Overview Strongylus vulgaris larvae migrate through the cranial mesenteric artery, causing arteritis, thrombus formation, and potentially thromboembolic colic from intestinal infarction. Clinical
## Overview Inflammatory bowel disease (IBD) in horses is chronic inflammatory infiltration of the intestinal wall. Subtypes include granulomatous, lymphocytic-plasmacytic, and eosinophilic enteritis
## Overview Intestinal lymphosarcoma is malignant infiltration of the gut wall by lymphocytes. Multicentric is the most common form of lymphosarcoma in horses; the intestinal (alimentary) form is les
Sudden changes in appetite, manure consistency, or signs of colic (pawing, looking at the flank, rolling) need prompt veterinary attention. Consistent high-quality forage and gradual diet changes support intestinal health.
## Overview Small colon impaction is obstruction of the descending (small) colon by dry ingesta. Horses show mild to moderate colic, straining to defecate, and reduced or absent manure. It is less common than large-colon impaction but can be serious because of the smaller diameter. ## Causes Dehydration, poor-quality feed, or reduced water intake. ## Diagnosis Rectal palpation of a firm impaction in the small colon and clinical signs. ## Treatment Fluids, lubricants, and analgesics. Surgery if medical treatment fails or the colon is damaged. ## Recovery and Prognosis Good with timely treatment. ## Prevention Adequate water and dental care. Signs include: mild to moderate colic; straining to defecate; small or absent fecal output
## Overview Small colon volvulus is rotation of the small colon that strangulates its blood supply. It causes severe colic and absent fecal output and is a surgical emergency. Delay leads to irreversible bowel damage. ## Causes Unknown predisposition to twisting. ## Diagnosis Severe colic, rectal findings, and confirmation at surgery. ## Treatment Immediate surgical correction and resection of any non-viable bowel. ## Recovery and Prognosis Guarded. Depends on the duration of strangulation. ## Prevention None. Signs include: severe colic; absent fecal output; surgical emergency
## Overview A fecalith is a hard, stone-like mass of inspissated feces that can obstruct the intestine, most often the small colon. It causes recurrent or progressive colic and straining. Miniature horses and foals are over-represented. ## Causes Dehydration, poor-quality roughage, dental disease, or reduced motility leading to fecal concretions. ## Diagnosis Rectal palpation (when reachable), ultrasound, and clinical signs of obstruction. Many are confirmed at surgery. ## Treatment Medical management with fluids and lubricants if the mass is reachable and softenable. Surgical removal for complete obstruction. ## Recovery and Prognosis Good if relieved before bowel compromise. Delayed cases risk rupture or severe illness. ## Prevention Adequate water, dental care, and appropriate forage. Signs include: recurrent colic; straining to defecate; reduced manure; abdominal distension in complete obstruction
## Overview Meconium impaction is retention of the foal’s first feces. Meconium is sticky material composed of intestinal secretions and swallowed amniotic fluid. Most foals pass it within 12 hours. Impaction causes straining, tail flagging, and colic in the first 1 to 4 days of life. Colts and post-term foals may be at higher risk. ## Causes Failure to evacuate the sticky meconium, sometimes related to weak nursing or dehydration. ## Diagnosis Clinical signs in a newborn, digital rectal examination, radiographs, or ultrasound showing the impaction. ## Treatment Enemas (warm soapy water or acetylcysteine retention enemas), oral laxatives, fluids, and pain relief. Most cases resolve medically. Surgery is rarely needed. ## Recovery and Prognosis Excellent with prompt treatment. ## Prevention Ensure the foal nurses well and monitor for passage of meconium in the first day. Signs include: straining; tail flagging; colic signs within the first 24 to 96 hours; abdominal distension
## Overview Strongylus vulgaris larvae migrate through the cranial mesenteric artery, causing arteritis, thrombus formation, and potentially thromboembolic colic from intestinal infarction. Clinical signs include recurrent colic, weight loss, intermittent fever, and diarrhea. Widespread use of modern dewormers has made clinical disease uncommon, but arterial lesions are still found in some populations. ## Causes Migration of Strongylus vulgaris fourth-stage larvae. ## Diagnosis Clinical signs, history of inadequate deworming, and sometimes ultrasound or surgical findings. Definitive diagnosis is often at necropsy. ## Treatment Anthelmintics and supportive care for colic. Infarcted bowel requires surgery. ## Recovery and Prognosis Variable. Acute infarction has a poor outlook. ## Prevention Regular strategic deworming that includes larvicidal activity against Strongylus vulgaris. Signs include: recurrent colic; weight loss; intermittent fever; diarrhea; may cause acute intestinal infarction
## Overview Inflammatory bowel disease (IBD) in horses is chronic inflammatory infiltration of the intestinal wall. Subtypes include granulomatous, lymphocytic-plasmacytic, and eosinophilic enteritis. It causes progressive weight loss, recurrent colic, variable diarrhea, and low blood protein from protein-losing enteropathy. ## Causes Unknown immune-mediated inflammation. Some cases follow parasitic or other antigenic stimulation. ## Diagnosis Exclusion of other causes of weight loss, low albumin, thickened intestine on ultrasound, and intestinal biopsy (often surgical). ## Treatment Corticosteroids are the mainstay. Dietary management and treatment of concurrent parasites. Response is variable. ## Recovery and Prognosis Guarded. Some horses stabilize; others continue to decline. ## Prevention None specific. Signs include: chronic weight loss; recurrent colic; diarrhea or normal feces; poor coat; hypoproteinemia; malabsorption
## Overview Intestinal lymphosarcoma is malignant infiltration of the gut wall by lymphocytes. Multicentric is the most common form of lymphosarcoma in horses; the intestinal (alimentary) form is less common. It causes progressive weight loss, recurrent colic, diarrhea, low protein, and ventral edema. Thickened intestinal loops are felt on rectal examination or seen on ultrasound. ## Causes Neoplastic. No specific cause is identified. ## Diagnosis Clinical signs, low albumin, thickened bowel on imaging, and biopsy or cytology confirming lymphoma. ## Treatment Chemotherapy protocols exist but responses are usually temporary. Most horses are managed palliatively and euthanized when quality of life declines. ## Recovery and Prognosis Poor. Survival is typically weeks to a few months after diagnosis. ## Prevention None. Signs include: progressive weight loss; recurrent colic; diarrhea; ventral edema; hypoproteinemia; thickened intestinal loops
Colic, enteritis, displacement, or impaction can involve any segment. Wall thickness can be measured with abdominal ultrasound. Malabsorption can be investigated with glucose or D-xylose absorption tests or biopsy in selected cases.
Sudden changes in appetite, manure consistency, or signs of colic (pawing, looking at the flank, rolling) need prompt veterinary attention. Consistent high-quality forage and gradual diet changes support intestinal health.
See the Intestinal Segment on our interactive 3D horse model. Open 3D Model