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Veterinary & Aquatic Services Department, Drs. Foster & Smith
Digestive System
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What is constipation?
Constipation is a clinical sign and not a disease process in and of itself. This condition is characterized by difficult, infrequent, or the absence of defecation. In addition, constipation often leads to the retention of excess fecal material in the colon and rectum. Excess fecal material in the colon and rectum can lead to other disease conditions such as megacolon. Pets suffering with this condition should be thoroughly examined by a veterinarian to determine the cause and appropriate treatment options.

Other related terms of interest:
  • Obstipation: when the colon is so full of fecal material that the colon is obstructed and defecation is not possible.
  • Dyschezia: difficult or painful defecation usually associated with lesions in or near the anus.
  • Tenesmus: straining to defecate, usually painful and unproductive; commonly associated with dyschezia.
  • Megacolon: a condition in which the colon becomes irreversibly dilated with fecal material and unable to function normally.

What causes constipation?
Constipation can be caused by a number of factors, diseases or conditions.

  • Ingestion of foreign material: Animals that ingest excess foreign materials like bone, plant materials, dirt, gravel, stones and/or hair can bulk-up, dry out and stiffen their fecal mass leading to constipation.

  • Environmental factors: There are a number of environmental factors that can lead to constipation in dogs and cats. Typically these are situations that place the animal outside their normal routine. Dogs or cats that are kenneled for an extended period of time or experience a prolonged stay at a veterinary clinic, may find these circumstances stressful to the point that normal bowel function becomes difficult.

    Certain cats may develop an aversion to their litter box. This may be because of the box's location, its size and/or shape, a change in the litter or a myriad of other reasons. The end result is the same; the animal retains their fecal mass until constipation develops.

  • Pain: There are a number of medical or orthopedic conditions that are painful and can lead to constipation. Anorectal diseases such as an anal gland impaction or an abscessed anal gland make the normal passage of stool painful. Orthopedic issues such as arthritic hip or knee joints can make the normal posture of defecation painful and the animal reluctant to defecate.

  • Obstruction: The dog or cat may develop an anal-colonic obstruction that prevents the normal passage of stool leading to constipation. Foreign bodies, such as a tumor, will slow or prevent the passage of feces. A perineal hernia or an enlarged prostate gland, can result in constipation. If the animal's pelvis has been fractured, the result after healing is most often, a narrower pelvic opening. A narrow pelvic opening can impinge on the colon and restrict the flow of fecal material leading to constipation.

    Another cause of anal obstruction which can lead to constipation is a condition known as "pseudocoprostasis." This occurs when the hair surrounding the anus becomes densely matted with fecal material, forming a blockage of the anal opening.

  • Neuromuscular diseases: At times there are neuromuscular disorders that interrupt the normal function of the lower colon. Intervertebral disc disease and/or spinal deformities in the lumbo-sacral region (pelvic area) of the spinal column can interrupt the evacuation of fecal material.

  • Metabolic disorders: Dogs and cats that experience metabolic disorders such as hypothyroidism or kidney failure may develop fluid and electrolyte imbalances such as hypokalemia (low potassium) and hypercalcemia (high calcium). These conditions can lead to dehydration, a decrease in colonic muscle contraction and fecal material that becomes dry and hard and is retained in the colon leading to constipation.

  • Medications: There are certain medications that can also cause constipation. Opiates, such as the pain medication morphine, often lead to constipation.

What are the symptoms of constipation?
The symptoms of constipation may seem obvious. However, we must carefully assess each animal carefully. There are many symptoms of constipation that are similar to other disease conditions involving the gastrointestinal tract. Animals with constipation are typically lethargic, dehydrated, reluctant to eat, may be vomiting and have a "hunched-up" appearance. In addition, these animals may experience tenesmus, dyschezia or a paradoxical diarrhea (the fecal material in the rectum stimulates the production of intestinal mucous that resembles diarrhea).

How is constipation treated?
Simple constipation: Your veterinarian will recommend that simple constipation be treated with an enema and/or an adjustment in the animal's diet.

Enemas containing soap and water, K-Y jelly or DSS (Docusate sodium) will usually relieve the symptoms of simple constipation. Do not give your cat or dog an enema unless instructed by your veterinarian to do so.

They may cause a severe electrolyte imbalance.

Rectal suppositories containing Glycerin, DSS or bisacodyl may be used to direct the medication to the site of the constipation.

Adjusting the amounts of fiber can modify the amount of stool produced by the animal. A high fiber diet can be fed to increase stool volume and stimulate the colon, leading to defecation. There are commercially available diets that are high in fiber or fiber can be added to the pet's normal ration. Additional fiber sources include: Metamucil (or similar product), canned pumpkin or bran cereal.

By contrast, feeding highly digestible foods, that are very low in residue, decrease the volume of stool producing an easier fecal load on the colon. These diets are typically prescription diets such as Hill's I/D or Iams low residue. Consult your veterinarian to discover which strategy would best serve your pet.

Severe constipation: Severe constipation occurs when the colon is dilated and packed with a large amount of hard, dry fecal material. At this point, the pet needs more veterinary care.

Giving a pet an enema and manually extracting a retained fecal mass is a challenging undertaking that is best left to the professionals at your veterinary clinic.

The first step in the treatment process is to discover, treat and/or manage the underlying condition that contributed to the constipation. Correcting any electrolyte imbalances to combat dehydration is especially important. The next step is to remove the impacted fecal material; this may require several sessions that include enemas and the manual extraction of the fecal material. This often requires anesthesia.

Medications available that can help relieve constipation
Stimulant laxatives, such as bisacodyl (Dulcolax) and cisapride, help move and expel the fecal mass.

Lubricant laxatives, such as the petrolatum-based products (Laxatone) or mineral oil, line the colon and prevent the loss of water from the stool. In addition, its lubricating properties help with the passage of stool through the lower colon.

Emollient laxatives, such as Docusate sodium (DSS), decrease the absorption of water from the fecal mass thereby preventing the desiccation of the stool. Do not mix DSS with mineral oil; DSS increases the body's absorption of mineral oil and the mineral oil may decrease the effect of the DSS.

There is an increased risk of aspiration pneumonia with mineral oil so this product should be used with great care; especially in cats.

Osmotic laxatives, such as lactulose or lactose, stimulate fluid secretion into the large intestine and increases the propulsion/expulsion of the fecal mass.

How is constipation prevented?

  • Identify, treat and manage all underlying and/or predisposing factors such as:
    • Metabolic disorders
      • Hypothyroidism
    • Orthopedic disorders
      • Osteoarthritis
    • Lesions near the anus or rectum that cause blockage
      • Swollen prostate gland
      • Perineal hernia
      • Anal gland abscess
      • Tumor
    • Prevent or minimize ingestion of constipating materials
      • Bones
      • Hair
      • Plant material
      • Dirt/ gravel
  • Manage megacolon
  • Encourage regular exercise
  • Always provide access to fresh water
  • Be aware of medications that can cause constipation
For cats
  • Address litter box issues
    • Maintain clean litter box(s)
    • Be aware of litter/litter box preferences
      • Brand of litter
      • Type of litter
      • Scent of litter
      • Depth of litter
      • Covered vs. uncovered litter box
      • Location of litter box

Constipation is not a disease in and of itself. It is a symptom of a disease; a result of some other condition. If your dog or cat demonstrates any of the symptoms of constipation listed above, please schedule an appointment with your veterinarian as soon as possible. As with most medical conditions, the sooner the underlying disease is diagnosed, the more favorable the outcome.

Diarrhea & Vomiting in Cats: When to Call Your Veterinarian 
Causes & Treatment of Diarrhea & Vomiting in Dogs 
Megacolon and Constipation in Cats 
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