CONDITION

Constipation and Megacolon

Why this matters now

Constipation is one of the most common gastrointestinal problems in cats, particularly affecting middle-aged to older animals. Certain factors may increase susceptibility, including obesity, dehydration, reduced activity, and diets low in fibre. Male cats appear somewhat more prone to developing megacolon, and some cases have an underlying neuromuscular component.

Constipation often begins intermittently, with occasional episodes of straining or reduced defecation frequency. Without management, the colon may become increasingly stretched and weakened over time. In megacolon, the colon loses its ability to contract effectively, becoming permanently dilated and incapable of normal function. This progression from simple constipation to megacolon can occur over months to years.

Signals & patterns

Early signals

Straining in the litter tray

Cats may spend extended time attempting to defecate, sometimes with visible effort but little result.

Hard, dry faeces

Stools may appear smaller than normal, dry, or pellet-like when passed.

Reduced frequency of defecation

Going longer than two days without passing faeces may indicate developing constipation.

Decreased appetite

Cats with faecal retention often eat less, likely due to abdominal discomfort or nausea.

Later signals

Vomiting

Severe constipation can trigger vomiting due to abdominal pressure and discomfort.

Visible abdominal distension

The abdomen may appear enlarged due to an impacted, distended colon.

Passing small amounts of liquid faeces

Paradoxically, liquid stool may pass around an impaction, sometimes mistaken for diarrhoea.

Lethargy and withdrawal

Cats with chronic constipation often become quiet and less interactive.

Click to read about the biological mechanisms

How this is usually investigated

Assessment of constipation involves physical examination, imaging to evaluate colonic size and content, and tests to identify any underlying causes.

Physical examination

Purpose: To assess hydration, palpate the abdomen for faecal material, and check for pelvic abnormalities
Considerations: A distended, firm colon is often palpable in affected cats. Rectal examination may reveal narrowing or obstruction.

Abdominal radiographs

Purpose: To visualise colonic size, faecal impaction, and any pelvic abnormalities
Considerations: X-rays show the extent of faecal retention and whether the colon is dilated. Pelvic fractures or narrowing may be identified.

Blood tests

Purpose: To check for dehydration, electrolyte imbalances, and underlying conditions
Considerations: Kidney disease, hypokalaemia (low potassium), and hypercalcaemia can contribute to constipation.

Thyroid testing

Purpose: To assess thyroid function in older cats
Considerations: Hyperthyroidism can affect gut motility and is common in older cats.

Options & trade-offs

Management depends on severity and chronicity. Approaches range from dietary modification to surgical intervention for refractory megacolon.

Dietary management

Increased fibre, adequate hydration, and sometimes wet food diets.

Trade-offs: Appropriate for mild cases. Some cats do better with higher fibre whilst others respond to lower-residue diets. Finding the right balance may take time.

Laxatives and stool softeners

Medications to increase water content of faeces or stimulate colonic movement.

Trade-offs: Various types work differently. May need regular or intermittent use depending on individual response. Some are given orally, others added to food.

Manual evacuation under anaesthesia

Removal of impacted faeces when severe obstipation is present.

Trade-offs: Provides immediate relief but does not address underlying cause. May need to be repeated in chronic cases. Requires anaesthesia.

Prokinetic medications

Drugs to enhance colonic contractions.

Trade-offs: May help cats with mild to moderate motility issues. Less effective once megacolon has developed.

Subtotal colectomy

Surgical removal of most of the colon.

Trade-offs: Considered for refractory megacolon when medical management fails. Most cats do well long-term, though initial loose stools are common.

Common misconceptions

Misconception:

"Cats that strain are always constipated"

Reality:

Straining in the litter tray can also indicate urinary problems or colitis with small frequent stools. Distinguishing between straining to defecate versus urinate is important.

Misconception:

"Constipation is just a minor inconvenience"

Reality:

Chronic constipation can cause significant discomfort, appetite loss, and may progress to megacolon if not managed. Early intervention often achieves better outcomes.

Misconception:

"Once a cat has megacolon, nothing can help"

Reality:

Many cats with megacolon can be managed medically for extended periods, and surgery can offer good quality of life when medical management is insufficient.

Observing litter tray habits including frequency, stool consistency, and any straining provides valuable baseline information. Noting water intake, activity levels, and appetite changes may help identify patterns. Multiple water sources and encouraging hydration through wet food can support digestive health.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS