Colitis/Diarrhea, Acute
Basic Information 
Clinical Presentation
History, Chief Complaint
• Usually, the horse has a history of depression, fever, inappetence, and mild colic signs, with or without diarrhea, lasting hours to days.
• Occasionally, the horse has an acute onset of severe colic signs and rapid systemic deterioration in the absence of diarrhea. Rarely, in peracute cases, horses are simply found dead.
Physical Exam Findings
• Variable signs of abdominal pain ranging from none to mild colic or inappetence to severe intractable colic
• Variable tachycardia (normal to 80–100 beats/min)
• Mucous membranes are often injected and may vary in color from bright pink to purple-gray.
• Capillary refill time may range from brisk (<1 second) in the early stages to dramatically prolonged (4–5 seconds) as severe dehydration and endotoxic or septic shock progress.
• There may be evidence of hypovolemia and poor peripheral perfusion (cold extremities, poor jugular refill) in severe cases.
• Hypermotile, “fluidy” gastrointestinal borborygmi
• Gross abdominal distension is occasionally present, especially in severe or peracute cases.
• Diarrhea may be absent or range from soft, formed feces to profuse, watery, or hemorrhagic diarrhea.
Etiology and Pathophysiology
• Initially, the colonic mucosal barrier is damaged focally or diffusely by one of the following:
• Loss of the colonic mucosal barrier allows intraluminal bacteria and bacterial toxins (eg, endotoxin) to invade the colonic wall, stimulating mural inflammation and edema.
• Bacteria and bacterial toxins are also then able to enter the intestinal lymphatic system and systemic circulation, resulting in clinical signs of endotoxemia and the systemic inflammatory response syndrome (fever, tachycardia, tachypnea, congested mucous membranes, and altered hemodynamic status and peripheral perfusion).
• In addition, the damaged mucosal barrier compromises colonic absorptive capacity, resulting in loss of water and electrolytes in the feces, and may permit loss of plasma proteins if the damage is severe.
• See sections “Cyathostominosis,” “Salmonellosis,” “Diarrhea, Clostridial,” “Potomac Horse Fever,” “Nonsteroidal Antiinflammatory Drug Toxicity,” “Colitis, Antimicrobial Associated,” “Colitis X,” “Blister Beetles,” and “Sand Enteropathy” in this section for more details.
Diagnosis 
Initial Database
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