SYMPTOM
Straining to defecate
Prolonged or repeated attempts to pass stool, often with visible effort, vocalisation, or posturing in the litter tray or outdoors without producing a normal bowel movement.
Constipation and Colonic Disease
Straining to defecate is the hallmark sign of constipation, where hard, dry faecal material is difficult to pass through the colon and rectum. In cats, chronic constipation may progress to megacolon, where the colon becomes permanently dilated and loses its contractile ability. The straining may be accompanied by vocalisation, prolonged positioning, and the production of only small, hard faecal pellets or no stool at all.
Colitis and Rectal Inflammation
Inflammation of the colon (colitis) or rectum (proctitis) can produce frequent straining to defecate, often with the production of small volumes of soft or mucoid stool, sometimes with blood. The straining in colitis reflects a frequent, pressing need to defecate and colonic irritability rather than mechanical difficulty passing stool, and the stools produced tend to be soft rather than hard, which helps distinguish it from constipation.
Rectal or Colonic Obstruction
Masses within the rectum or distal colon, including polyps, tumours, or strictures from previous inflammation or surgery, can physically impede the passage of faecal material, producing straining as the animal attempts to move stool past the obstruction. The straining may be progressive as the obstruction grows, and the stools may change shape or become ribbon-like.
Pelvic or Perineal Disease
Conditions affecting the pelvic region (including previous pelvic fractures with canal narrowing, perineal hernias, or anal gland disease) can create mechanical barriers or pain-associated inhibition of defecation. Perineal hernias in dogs allow pelvic organs to displace into the perineal region, potentially trapping faeces and making defecation difficult. If the bladder is displaced into the hernia, the flow of urine can be blocked as well.
Neurological
Conditions affecting the sacral spinal cord segments or the nerves supplying the colon and rectum can impair the coordinated muscular contractions needed for effective defecation. Sacral spinal disease, cauda equina syndrome, and dysautonomia can all produce chronic straining and constipation through disrupted nervous control of colonic and rectal function.
Why timing matters
Early observation
Early straining to defecate may present as slightly prolonged time spent in the litter tray or defecation position, with the animal producing stools that are somewhat harder or smaller than usual. The episodes may be intermittent, with normal defecation occurring between bouts of straining. At this stage, the cause may be transient (dietary indiscretion, mild dehydration, or environmental stress) and may resolve, but the early picture alone does not show which cause is present. Where the straining is in fact an attempt to pass urine through a blocked urethra, the timescale is different: with a complete blockage, severe illness develops within 36 to 48 hours and death follows within approximately 72 hours.
Later presentation
Persistent or worsening straining suggests an ongoing process that is unlikely to self-resolve. The animal may spend increasingly long periods attempting to defecate, producing very little or no stool despite repeated efforts. Vocalisation during straining, visible distress, and association of the litter tray or defecation area with discomfort may develop. Some animals may begin defecating in inappropriate locations, associating their usual spot with pain. Blood may appear on the stool surface or in the litter tray from mucosal trauma caused by the passage of excessively hard stool.
The trajectory of straining depends on the underlying cause. Constipation-related straining tends to follow a pattern of escalating frequency and severity as colonic function deteriorates, with progressively shorter intervals between episodes requiring intervention. Colitis-related straining may fluctuate with the activity of the inflammatory process. Obstructive causes typically produce progressive worsening as the obstruction grows. Understanding whether the straining is getting worse, staying stable, or occurring in episodes helps characterise the underlying process.
Conditions commonly associated
Constipation and Megacolon in Cats
Straining to defecate is the defining clinical sign of constipation and megacolon, reflecting the difficulty of propelling hard, dry faecal material through a progressively dysfunctional colon.
Anal Gland Disease in Dogs
Impacted or infected anal glands can cause discomfort during defecation, leading dogs to strain or show reluctance when attempting to pass faeces.
Colitis
Straining to defecate is a characteristic sign of colitis, as the irritated large bowel creates a persistent sensation of needing to eliminate even when empty.
Prostate Disease
Prostatic enlargement can compress the rectum, causing difficulty passing faeces and altered stool shape.
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Anal Sac Adenocarcinoma
A tumour growing within or around the anal sac can narrow the rectum, making bowel movements difficult and causing visible straining.
Anal Furunculosis (Perianal Fistulas)
Painful, ulcerating tracts around the anus make passing stool uncomfortable, leading affected dogs to strain during defecation.
Intestinal Intussusception
The telescoped segment of bowel partly or completely blocks the intestine. The scant bloody diarrhoea it can cause, often with vomiting and abdominal pain, may be seen as straining with little stool passed.
Prostatic Hyperplasia
An enlarged prostate sitting beneath the rectum can narrow the space stool must pass through, which can make bowel movements harder work, although many dogs with an enlarged prostate show no such sign.
Rectal Prolapse
Persistent straining, whether from the underlying cause or the prolapse itself, makes bowel movements appear difficult and drawn out.
Tritrichomonas Foetus in Cats
The inflammation this infection causes in the colon leads to frequent passage of small amounts of liquid to semi-formed faeces, with some straining.
Urethral Obstruction
Repeated straining to pass urine through a blocked urethra looks very like straining to defecate, and owners sometimes mistake it for constipation.
Constipation and Megacolon
Straining with the passage of firm, dry faeces is the main sign of constipation in both dogs and cats.
When to explore further
Repeated straining that produces little or no stool can reflect faecal retention, a blockage of the bowel or a blocked urethra, and these cannot be reliably told apart at home. Obstipation is constipation so severe that the animal is unable to pass the mass of hard, dry faeces, and ill animals may also show lethargy, loss of appetite, vomiting (especially cats) and abdominal discomfort.
Straining to urinate and straining to defecate can look very similar, particularly in cats, and owners sometimes mistake a blocked urethra for constipation. Urethral obstruction mostly affects male cats and male dogs. With a complete blockage, severe illness develops within 36 to 48 hours and death follows within approximately 72 hours if the blockage is not relieved. It can be difficult to tell from the posture which of the two is happening, so an animal that strains repeatedly and passes little or nothing cannot be assumed to be constipated.
Straining accompanied by the passage of bloody or mucoid stool, without the hard, dry faeces typical of constipation, may suggest colitis or rectal disease rather than simple constipation.
Progressive worsening of straining episodes over weeks to months, with each episode requiring more intervention to resolve and shorter symptom-free intervals between episodes, may suggest a deteriorating underlying condition.
Straining to defecate in an animal that has had previous pelvic trauma, spinal disease, or abdominal surgery may suggest a structural or neurological factor contributing to the difficulty.
Noting the frequency of defecation, the size and consistency of stools produced, and the amount of time spent straining provides objective data that can reveal trends over time, although it does not show whether the straining is faecal or urinary. Comparing the animal's current defecation pattern against its previous baseline helps identify whether the straining represents a new development or a worsening of a pre-existing pattern.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS