Constipation in dogs: symptoms, causes and treatment

Overview

Constipation is often temporary. Faeces remaining in the large intestine dry out, making passage more difficult. In severe impaction, a dog cannot evacuate the hardened mass unaided.

Persistent or recurrent constipation warrants investigation for an internal obstruction, external pressure or impaired bowel function slowing passage. Megacolon means an enlarged colon with reduced ability to move faeces onwards. Severe constipation may need hospital care if fluids or repeated evacuation are required.

The large intestine reabsorbs water before defaecation. Most dogs pass faeces at least once daily, although the pattern may follow mealtimes.

Causes

Muscle contractions in the bowel wall move faeces towards the rectum. A meal can trigger stronger waves of colonic contraction. If propulsive contractions weaken, faeces can remain in the colon too long. Poorly digested bone fragments can mix with faeces and form a difficult-to-pass mass.

An enlarged prostate can press on the rectum and narrow the passage. A pelvic fracture healing out of alignment can narrow the space through which the rectum passes. A rectal tumour can obstruct faecal passage. Spinal cord or pelvic nerve disease can disrupt bowel movement.

Hypothyroidism can affect colonic movement. In a perineal hernia, muscle support at the rear of the pelvis weakens and the rectum may lose support. Anal sac inflammation can make defaecation painful and cause straining.

Low blood potassium may be associated with poor colonic movement. In some cases, an enlarged lymph node narrows the rectal passage. Swallowing large amounts of hair can add poorly digested material to faeces.

An internal scar-related narrowing can slow passage through the colon. Increased contractions that mix rather than propel contents can also predispose to constipation.

Risk factors

Insufficient drinking predisposes to hard, dry faeces. A dog may start holding faeces if defaecation hurts. A nervous dog may withhold faeces in stressful surroundings. Constipation can be a side effect of medicines such as opioids or diuretics.

Perineal hernia is one possible cause, particularly in uncastrated males. It is often found at seven to nine years old. In one study from northern Europe, owners reported chronic constipation before hernia-associated symptoms in 14 of 66 dogs with perineal hernias, or 21.2%.

Osteoarthritis pain can make positioning and defaecation difficult. Little exercise can predispose to constipation. In a northern European comparison, dogs with perineal hernias had larger prostates than controls.

Long-haired dogs and those licking themselves excessively may be at greater risk. Benign prostate enlargement is common in uncastrated males over six.

Typical symptoms

A constipated dog may take up the defaecating position more often without passing faeces. Reduced output is easier to recognise if the dog's normal pattern is familiar.

• Only small, hard, dry pieces may be passed.
• The abdomen may be tender to touch.
• The abdomen may feel tight.
• Appetite may decrease.
• A severely affected dog may vomit.
• Faeces may look ribbon-like when the prostate presses on the rectum.

Colitis can also cause straining, often with small amounts of loose, mucoid faeces. A bulge beside the anus alongside difficulty defaecating may suggest a perineal hernia.

A little watery faeces may seep around a hard mass. A small amount of blood may appear with straining. A painful dog may vocalise when trying to defaecate. Severe constipation can make a dog subdued.

Complications and consequences

Prolonged stretching from accumulated faeces can weaken colonic contractions. An enlarged, poorly contracting colon may then collect even more faeces. Very severe impaction can perforate the colonic wall. Faeces entering the abdominal cavity can cause life-threatening peritonitis.

The bladder can turn backwards into a position that prevents urine flow. Blood supply to a bowel loop trapped in a hernia can be compromised. Some dogs continue to have defaecation problems even after successful perineal hernia repair.

The outlook for persistent constipation depends mainly on what prevents bowel emptying.

A serious underlying disease may require lifelong medication or dietary management.

Diagnosis at the vet

History and examination

The vet asks how long symptoms have lasted and what the dog may have eaten beforehand. A previous pelvic injury can matter even after healing. Feeling the abdomen may reveal a colon full of faeces. Rectal examination checks for a foreign body or painful area, for example.

In males, prostate size can also be assessed through the rectum. If neurological disease is suspected, function of the rear part of the spinal cord is examined particularly. Pain or difficulty moving the hindlegs may prompt examination of the hips and lower lumbar region.

If urinary obstruction is suspected, the vet may feel the bladder for enlargement and tenderness.

Imaging and samples

Abdominal X-rays assess faecal accumulation and possible obstruction. Bone fragments within the faeces may be visible. Ultrasound can look for an external obstruction, such as an enlarged prostate. Colonoscopy can investigate whether an internal narrowing causes recurrent constipation.

Blood tests can assess dehydration and other underlying diseases. Thyroid hormone may also be checked in recurrent cases. If a rectal tumour or narrowing is suspected, a tissue sample can help identify the lesion.

In one nine-year-old male dog, X-rays showed that impacted faeces and an enlarged prostate narrowed the faecal passage. The same dog had no significant blood count or biochemistry changes.

Urine testing helps assess possible concurrent disease in chronic or recurrent constipation.

Treatment

Mild constipation and dehydration

For mild constipation in an otherwise well dog, care may start with adequate drinking and dietary changes. Suitable fibre content depends on the cause. Fibre can retain water and soften faeces. Dehydration should be corrected before adding fibre, as fibre in a dry bowel can worsen impaction.

The vet may prescribe a stool-softening medicine. Lactulose, for example, softens faeces by retaining water in intestinal contents. A stimulant laxative is used only after obstruction has been excluded. A dehydrated dog may receive intravenous fluids to help soften intestinal contents.

The vet may choose a prokinetic medicine if poor bowel movement contributes to constipation.

Dehydration is corrected before a laxative is given, as the medicine could otherwise worsen fluid loss.

Removing impacted faeces

For severe constipation, the vet may perform an enema or bowel lavage. If flushing is insufficient, hardened faeces can be removed under general anaesthesia. Removal may need two to three procedures over several days. Fluid and electrolyte disturbances are corrected at the same time.

Removal of a severely enlarged, permanently poorly functioning part of the colon may be considered if other treatment fails. Constipation from a perineal hernia may require surgical repair. When an enlarged prostate impedes passage, treatment also aims to reduce its size.

A breathing tube may protect the airways during disimpaction because the procedure can trigger vomiting. In the individual prostate-enlargement case, enemas relieved impaction within two days.

The dog treated for prostate enlargement and impaction had follow-up prostate ultrasound 60 and 180 days after discharge.

Prevention

Keep fresh drinking water easily accessible, as adequate hydration helps prevent faeces drying out. Regular outings allow bowel emptying before faeces harden. A balanced diet and suitable exercise may help prevent mild constipation.

If your dog is prone to constipation, avoid bones and other poorly digestible pieces. Sharp bone fragments can also damage the intestine. A high-fibre food may be selected to prevent recurrence in a dog with previous constipation.

Short, gentle lead walks can support bowel movement if the dog is otherwise well. Limiting bone intake reduces the risk of poorly digested material causing an obstruction.

Important for dog owners

Record when your dog last passed faeces and what they looked like. On walks, check whether a straining dog passes urine normally. Tell the vet about possible access to bones, rubbish or other hard material. Mention medication changes and recent surgery too.

Contact a vet if no faeces are passed for 48–72 hours after the last bowel movement. Seek immediate care for repeated unsuccessful straining. Human laxatives can harm dogs.

After surgery, defaecation may be delayed for one to two days if the dog has eaten and moved less than usual. Report reduced drinking after surgery to the treating practice. Contact a vet if appetite disappears during constipation.

Frequently asked questions

When is straining an emergency?

Repeated unsuccessful attempts to defaecate require urgent assessment. If your dog tries to urinate without success or passes only drops, seek emergency care immediately. Attempts to urinate during obstruction can look like defaecation straining to an owner.

Can watery faeces occur with constipation?

A little liquid faeces can escape past a hardened mass. Colitis can also cause straining and small amounts of looser-than-usual faeces. Feeling the abdomen can help the vet establish whether much hard faeces remains in the colon.

Does fibre always help constipation?

Fibre can retain water and soften faeces in the colon. Adding it requires correction of dehydration first. Depending on the cause, a low- or high-fibre diet may be selected.

How does a vet remove impacted faeces?

For severe constipation, the vet may try to soften impacted faeces with an enema. If flushing is inadequate, the mass can be removed mechanically under general anaesthesia. Emptying the bowel can take several days and sometimes two to three procedures.

Why is defaecation slower after surgery?

Bowel emptying may be delayed for one to two days after surgery. Reduced appetite, painkillers and less exercise can all affect the pattern. Contact the treating practice if difficulties persist or straining is marked.