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Constipation (Severe) in Dogs

Megacolon in Dogs

Megacolon refers to the abnormal enlargement of the colon due to the retention of waste, particularly associated with chronic constipation or obstipation in dogs. The colon, part of the large intestine, serves as a temporary storage site where water and salt are extracted from waste. Megacolon occurs when waste remains in the colon, causing it to become abnormally enlarged.

This condition can be congenital or acquired. In congenital megacolon, dogs are born with an abnormal lack of smooth muscle function in the colon. On the other hand, acquired megacolon can develop when feces are chronically retained, leading to complete absorption of fecal water and solidification of waste within the colon. Prolonged retention of solidified feces can cause distention of the colon and irreversible colonic inertia, where the smooth muscle of the colon fails to contract or expand to expel feces.

Symptoms and Types

Symptoms and types of megacolon in dogs include:

  • Constipation: Feces are trapped in the colon.
  • Obstipation: Severe blockage that hinders both feces and gas, keeping them trapped in the colon.
  • Infrequent defecation.
  • Straining to defecate with small or no fecal volume.
  • Small amount of diarrhea may occur after prolonged straining.
  • Hard, dry feces.
  • Hard colon felt during abdominal examination (palpation).
  • Fecal impaction can be felt when a gloved finger is inserted into the rectum.
  • Occasional vomiting, anorexia, and/or depression.
  • Weight loss.
  • Dehydration.
  • Scruffy, unkempt hair coat.


Causes of megacolon in dogs include:

  • Idiopathic (unknown)
  • Congenital (present at birth)
  • Mechanical obstruction of feces
  • Trauma to the body, such as limb and/or pelvic fractures
  • Metabolic disorders, including low serum potassium and severe dehydration
  • Drugs like Vincristine (used for lymphoma and leukemia), Barium (used for enhancing x-ray images), Sucralfate (used for treating ulcers), and antacids
  • Neurologic or neuromuscular diseases
  • Spinal cord disease
  • Intervertebral disk disease
  • Diseases affecting the anus and/or rectum


Diagnosis of megacolon in your dog involves several steps. Your veterinarian will conduct a comprehensive physical examination, including an abdominal palpation to assess the colon’s condition. A digital rectal examination will also be performed to evaluate the rectum.

Furthermore, your dog will undergo various tests, including a complete blood profile, chemical blood profile, complete blood count, electrolyte panel, and urinalysis. Providing a detailed history of your dog’s health, including the onset of symptoms and any relevant incidents, is essential for accurate diagnosis.

Abdominal radiographs will be taken to visually inspect the colon for fecal accumulation, presence of blockages, or any underlying causes contributing to megacolon. If necessary, an internal examination of the colon using a colonoscope may be conducted to identify obstructive lesions or abnormalities within the colon wall that cannot be detected through other means.


Treatment for megacolon typically involves hospitalization for initial fluid therapy to rehydrate the body and correct electrolyte imbalances. Once stabilized, the colon can be gently evacuated. Your veterinarian will administer anesthesia to your dog and then use warm water enemas and water-soluble jelly to facilitate the extraction of feces with a gloved finger or sponged forceps.

In cases where medical management is ineffective, especially with irreversible colonic inertia, surgery may be necessary to repair the colon. Subtotal colectomy surgery is often performed to address recurrent megacolon, offering a potential cure for affected dogs.

Living and Management

Living and managing a dog with megacolon involves several important considerations. Regular exercise and activity are strongly recommended to promote the health and strength of the digestive and abdominal muscles.

A low-residue, high-fiber diet is beneficial in preventing recurrences of megacolon. Additionally, you can supplement your dog’s regular diet with veterinarian-approved fiber supplements or canned pumpkin (not pumpkin pie filling) to support digestive health.

It’s crucial to avoid feeding bones to your dog to prevent potential injuries to the colon and blockages in the intestinal tract caused by partially digested bone fragments. By adhering to these dietary and lifestyle recommendations, you can help manage your dog’s condition and promote their overall well-being.

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