Constipation in Dogs

By Malcolm Weir, DVM, MSc, MPH; Ernest Ward, DVM

What is constipation?

Constipation is infrequent or difficult passage of stool or feces and is typically a temporary condition. Many constipated dogs will experience straining or pain when attempting to defecate. Obstipation, a severe form of constipation, is often associated with a serious, permanent, or irreversible medical condition.

Since one of the major functions of the colon is water absorption, sometimes the retained stool becomes hard and dry, which makes passing it even more difficult. In some cases, dogs may become dehydrated. Some constipated dogs may pass small amounts of liquid feces or blood due to their excessive straining. Sometimes, the liquid feces are mistaken for diarrhea, but actually, when the dog strains, a small amount of liquid fecal material is able to squeeze around the hard fecal mass.

What causes constipation?

There are many potential causes of constipation in dogs. The most common cause is ingestion of irritating or indigestible substances. Dogs with long hair or those that lick or groom themselves excessively are also at risk for becoming constipated.

Other common causes of constipation in dogs include:

  • diseases of the colon
  • drugs that cause constipation (such as antihistamines, diuretics, narcotic pain relievers, and sucralfate)
  • fear, anxiety, and other behavioral conditions that alter passage of normal bowel movements
  • foreign bodies or intestinal obstruction
  • hormonal diseases (hypothyroidism, hyperparathyroidism)
  • inadequate exercise and physical activity
  • megacolon (enlarged colon)
  • neurologic diseases
  • painful conditions, such as osteoarthritis that make it uncomfortable to pass stool
  • pelvic injuries or abnormalities
  • sudden change in diet or ingestion of new foods
  • tumors or masses in the colon or rectum

How can I tell if my dog is constipated?

Most dogs produce feces at least once a day; many of them have bowel movements that correspond to the number of daily feedings. If your dog is constipated, he or she will probably attempt to pass feces unsuccessfully several times. You may observe your dog circling excessively, scooting (dragging bottom along the ground) or squatting frequently, or even crying out in severe cases. Other clinical signs include decreased appetite, vomiting, small amounts of watery feces or feces that contains mucus (without a normal stool), and weight loss. Some constipated dogs will have a tense, painful abdomen and cry or growl if you press on their stomach or lower back.

Call your veterinarian if your dog fails to produce a bowel movement within 48 to 72 hours of a previous bowel movement.

How is constipation diagnosed?

Most cases will be diagnosed through a physical examination and medical history. When evaluating your dog’s abdomen, your veterinarian will likely feel a firm, distended colon. He or she may conduct a rectal examination to rule out rectal strictures (a narrowing of the exit passage, resulting from a previous problem), tumors, foreign bodies, or other abnormalities. In many cases, abdominal radiographs (X-rays) will be performed to determine the extent of constipation and whether or not an obstruction exists. Blood tests and urinalysis are valuable to search for dehydration or infection. In advanced cases, an abdominal ultrasound may help identify the cause of your dog’s constipation. Biopsies may also be recommended if a rectal mass or stricture is suspected.

How is constipation treated?

Most cases of constipation are relatively easy to treat. The first step is to loosen or remove the impacted, hardened fecal matter. Removal may be accomplished through the use of one or a combination of therapies, including enemas, manual removal, and medications. Medications such as dioctyl sodium sulfosuccinate (DSS) (brand name Ducosate®) or lactulose (brand names: Cephulac®, Kristalose®, Generlac®, Constulose®, Enulose®) are commonly prescribed. In cases where stimulant laxatives are required, drugs such as cisapride (brand names: Prepulsid®, Propulsid®) or tegaserod, may be recommended.

Some dogs may require hospitalization while undergoing multiple enemas or to replace fluids to correct dehydration. More serious conditions may require additional treatments, including surgery or lifelong medical or dietary management. Either a low- or high-fiber diet may be needed based on your pet’s specific cause of constipation. Dogs that have behavioral or psychogenic causes of constipation may need behavioral modification through training and/or medications. Supplements such as probiotics may also be used after the constipation has been corrected.

What is the expected outcome for constipation?

The prognosis for constipation is determined by the exact cause. Most dogs will enjoy a speedy recovery after medical treatment has been completed. For dogs with more serious underlying diseases that cause constipation, the prognosis is good once the causative condition has been addressed. Most dogs can be successfully managed through a combination of medical, dietary, and surgical treatments.

"The prognosis for constipation is determined by the exact cause."

A serious, though generally uncommon, consequence or cause of constipation in dogs is megacolon. Megacolon refers to a dilated and weak colon that causes severe constipation. In this condition, the weakened muscles of the colon fail to propel fecal matter out of the colon. This may be due to neurological impairment, problems with the muscles lining the colon, or both. Megacolon may be seen as a primary condition or secondary following long-term constipation. When the colon becomes enlarged with fecal material over an extended period, its ability to contract may be reduced or lost, resulting in megacolon. Feces accumulate in this abnormally distended and enlarged colon.

How can I prevent my dog from becoming constipated again?

Based on the exact cause of your dog's constipation, your veterinarian may advise you to feed a therapeutic diet, add supplements or medications to the food, or return for additional tests or treatments. For the majority of dogs, constipation is directly related to eating an unfamiliar food or object and further medical intervention is unnecessary. Other dogs may require lifelong treatment to help maintain normal bowel movements.

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