Constipation — infrequent or difficult defaecation — is a significant welfare problem in cats. Chronic constipation can progress to obstipation (complete inability to defaecate) and megacolon, causing severe and prolonged suffering. Early recognition and treatment is essential.
Most cats defaecate once or twice daily. Frequency varies with diet — high-fibre diets increase frequency, wet diets reduce frequency. Monitoring normal patterns for individual cats helps identify early changes.
Dietary factors: Low fibre intake, insufficient water intake (particularly dry food-fed cats), and ingestion of indigestible material (hair, bones, foreign objects) are the most common causes.
Environmental factors: Litter box aversion due to location, cleanliness, type of litter, or competition from other cats causes many cats to withhold defaecation, allowing faeces to dry out and harden.
Pain: Anal sacculitis, perineal injuries, or musculoskeletal pain that makes squatting uncomfortable causes constipation through voluntary withholding.
Neuromuscular disease: Dysautonomia, sacral nerve injuries from tail pull trauma, and disc disease impair colonic motility.
Obstruction: Pelvic fracture malunion, intraluminal masses, or extraluminal compression narrows the pelvic canal.
Idiopathic megacolon: The most severe form in cats — progressive loss of colonic smooth muscle function causing an atonic, massively dilated colon. The cause is poorly understood but may represent end-stage constipation in predisposed cats.
Constipated cats experience significant discomfort. They may strain repeatedly in the litter box, cry during attempts to defaecate, and show general signs of malaise including reduced appetite, lethargy, and pain behaviours. Cats with megacolon suffer chronic abdominal distension and nausea. The repeated cycle of veterinary enemas and manual decompressions causes significant iatrogenic stress in recurrent cases.
Abdominal palpation reveals faecal impaction in mild cases. Radiography confirms the diagnosis, assesses the degree of colonic distension, and identifies pelvic abnormalities or spinal disease. Blood tests exclude metabolic causes including hypokalaemia, hypercalcaemia, and hypothyroidism. Neurological examination assesses perineal reflexes. Colonoscopy may be indicated in refractory cases to identify structural abnormalities or mucosal disease.
Mild constipation: Dietary management is the foundation — increasing wet food, adding water to food, dietary fibre supplementation (psyllium husk, pumpkin), and litter box optimisation.
Moderate constipation: Osmotic laxatives (lactulose, polyethylene glycol) or stool softeners may be prescribed. The prokinetic drug cisapride significantly improves colonic motility and reduces recurrence.
Severe obstipation: Manual decompression under anaesthesia, warm water enemas, and parenteral fluid therapy are required. Repeat episodes require more aggressive maintenance therapy.
Megacolon: Subtotal colectomy — surgical removal of most of the dysfunctional colon — provides good long-term outcomes for many cats with idiopathic megacolon. Post-surgical diarrhoea typically resolves within weeks to months.
Preventive measures include: wet food-based diet or water fountains to increase hydration, regular grooming to reduce hairball ingestion, clean and accessible litter boxes (one per cat plus one extra), environmental enrichment to reduce stress (which impairs gut motility), and maintaining healthy body weight (obese cats have higher constipation risk).
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