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Key takeaways

Megacolon in dogs describes abnormal dilation of the lower intestines, which prevents normal passage of feces.

  • Megacolon is a rare condition in dogs, most commonly seen in geriatric patients
  • Megacolon can lead to permanent colon damage
  • The most common symptoms are constipation or straining to defecate
  • Other symptoms include weight loss, bloody stools, dry or hard feces, vomiting, and abdominal pain
  • The diagnostic process usually consists of a physical examination, bloodwork, diagnostic imaging of the abdomen, and colonoscopy -Treatment includes enemas, IV fluid therapy, palliative care, laxatives, and manually removing feces
  • Severe or chronic cases might need surgery
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A closer look: Megacolon in Dogs

The colon is the lower part of the intestines (also referred to as the large bowel). In healthy individuals, the colon absorbs water as food proceeds through the final stages of digestion. Muscular contraction of the colon pushes feces through the system for passage out of the body. In cases of megacolon, the colon expands and becomes less effective at contracting, leading to constipation as movement of feces slows.

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Risk factors

Megacolon is rare in dogs. Prompt medical attention is warranted to prevent further damage to the colon and permanent dilation.

If not promptly diagnosed and treated, megacolon can develop into chronic constipation and permanent damage to the colon. This more serious stage of the condition is only treatable with surgical intervention. Any dog who has not had a bowel movement in 3 days requires prompt medical attention.

Possible causes

There are three main forms of megacolon in dogs.

Hypertrophic megacolon is usually caused by an obstructive lesion that results in an accumulation of feces and a dilated colon. Examples include pelvic fractures, tumors, or perineal hernia.These obstructions cause feces to accumulate in the colon, leading to dilation.

Neurogenic megacolon is the result of a neurological disorder that disrupts the nerve signaling pathways of the large bowel. This leads to reduced ability to relax the rectum when stimulated by the passage of feces. The colon responds by expanding to accommodate the continuing build up of feces behind the blockage originating from the rectum.

In some cases megacolon can be idiopathic, meaning that the underlying cause cannot be determined.

Main symptoms

Testing and diagnosis

The diagnostic process begins with symptoms observation such as changes in defecation habits and a complete physical examination, including abdomen palpation. Other tests include:

  • Bloodwork
  • Diagnostic imaging such as X-rays or ultrasound of the abdomen
  • Colonoscopy
  • Contrast study of the gastrointestinal tract (CT scan)

A neurological examination might also be necessary.

Steps to Recovery

Treatment initially focuses on the management of clinical signs and might involve:

  • Enemas
  • Intravenous (IV) fluid therapy
  • Deobstipation, which consists of manually removing feces from the bowel

In cases of chronic megacolon with permanent damage to the colon, surgery (subtotal colectomy) might be necessary; before considering a colectomy, a veterinarian might use other measures such as:

  • High-fiber diet
  • Laxatives
  • Palliative therapy

With adequate treatment of any underlying condition causing megacolon, the prognosis is usually positive. In chronic cases, dogs might need permanent medical attention but it usually consists of a manageable change in dietary habits.


Megacolon is not contagious. Preventive measures include a high fiber diet, proper hydration, proper electrolyte balance, and avoiding dietary indiscretion. Recognizing symptoms of constipation early in dogs can also allow for earlier treatment, leading to better prognosis. Any dog who has not had a bowel movement in 3 days requires prompt medical attention.

Is Megacolon in Dogs common?

Megacolon is a rare condition in dogs.

Typical Treatment

  • Manual deobstipation
  • Laxatives
  • IV fluid therapy
  • Edemas
  • High fiber diet
  • Subtotal colectomy

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