08.Apr 2022

Animal nutrition: Constipation - common causes, simple dietary measures and peculiarities in megacolon



Constipation is usually manifested by tenesmus with absent or greatly reduced defecation, sometimes pseudodiarrhea occurs. Other associated symptoms may include vomiting, anorexia, and lethargy.

The most significant differential diagnosis is dysuria or anuria.

Poor general condition, abdominal pain, or high-frequency vomiting may be indicative of a life-threatening emergency such as an ileus.

Causes of difficult or absent defecation can be:

  • foreign bodies, (tricho)bezoars
  • chronic / severe fluid deficiency or dehydration
  • malnutrition (e.g. lack or excess of raw fiber, bone feeding)
  • diseases of the gastrointestinal tract (e.g. megacolon)
  • Male dogs: perineal hernias and/or prostatic hyperplasia
  • pain during defecation (e.g. hip joint diseases, spondylosis)
  • spinal cord diseases (e.g. disc prolapse, cauda equina syndrome)  
  • stenoses/strictures of the intestine (e.g. tumors) or of the pelvic bones (e.g. old fractures)
  • various diseases of the anal region
  • psychological stressors, lack of possibility to defecate in a relaxed way (especially cats)
  • rare reasons: neurological diseases like dysautonomia, pyometra, high grade parasite infestation, anatomical malformations (e.g. atresia ani, Manx syndrome of cats)
  • side effects of drug therapy (e.g. diuretics, opioids, barium sulfate)
  • age: lack of exercise, lower intestinal activity, malnutrition
  • partly endocrine causes have a favorable effect, e.g. hypothyroidism

What to do in case of constipation?

In addition to pharmacologically active drugs or rectal enemas/microenemas, the following dietary measures may be useful in acute cases of simple constipation with an undisturbed general condition and for prophylaxis:

Mild laxatives:

  • Milk: maximum daily amount about 20 ml/kg bw (usually short-term use, exceeding this amount can cause malfermentation in the colon and diarrhea)
  • Lactulose: 0.6 ml/kg bw/day, distributed over several portions (long-term use possible; most common agent)
  • Macrogol (polyethylene glycol) - use in veterinary medicine still relatively young, many success stories in practice
  • The use of pure paraffine oil must be carefully selected, as accidental entry into the respiratory tract can cause life-threatening aspiration pneumonia (lipid pneumonia).

Stimulation of intestinal activity by increasing the fiber content, simultaneous prebiotic effect:

  • Psyllium (psyllium husks): About 2-10 g, depending on size in small animals, in horses up to about 50 g. Important: swell beforehand with enough hot water, so that the psyllium does not extract further water from the intestinal contents
  • Wheat bran: Approx. 1g/kg bw, soak beforehand
  • Linseed: 5-10 g/dog, approx. 100 g/pfd - pour hot water generously over it and let it swell for 10 min
  • Carrots and apples: Raw, grated or cooked
  • Feed cellulose: Approx. 0.5 g - 1 g/kg bw
  • Adding vegetable oil is also possible (Pfd. approx. 100 ml, dog and cat 1-3 tsp.)

Note: When feeding swelling substances, it is essential that the patient is sufficiently hydrated, otherwise constipation or dehydration may be forced!

The quantities stated are guidelines - please also observe the respective manufacturer's instructions.

Special feeding management for megacolon

Megacolon is a disease that occurs regularly in cats, but is comparatively rare in dogs. The chronic dilatation of the large intestine with hypomotility results in the accumulation of fecal masses and the associated chronic constipation.

Conversely, chronic constipation can also cause megacolon.

High-fiber diets are contraindicated in megacolon because they increase fecal volume and thus mural pressure - which promotes further damage to the intestinal wall musculature and exacerbation of symptoms.

Rather, the goal of feeding management in megacolon is to keep fecal volume as low as possible. This is usually achieved by feeding highly digestible moist feed. Regular administration of laxatives will assist in moving the feces along.

Do you have any further questions about the dietary management of your patients?

Our Diplomates ECVCN/ACVN will gladly support you by promptly preparing case-based nutrition plans as well as answering further questions regarding dietary support in therapy.


Bibliography: Upon request

Author of the article:

Veterinarian med. vet. Julia Brüner