SYMPTOM
Bloody diarrhoea
Owners may observe bloody diarrhoea in their pet.
Various conditions
This symptom can occur in multiple conditions and warrants further assessment.
Infectious Enteritis (Bacterial And Viral)
Organisms such as Campylobacter, Salmonella, and canine parvovirus damage the intestinal lining directly, allowing blood and plasma proteins to leak into the gut and appear in the stool alongside mucus. Parvovirus is most often seen in unvaccinated puppies and produces profuse, often haemorrhagic diarrhoea with marked lethargy, while bacterial causes can affect dogs of any age, particularly after scavenging or contact with raw diets. Onset is typically rapid, over one to two days.
Intestinal Parasites
Whipworm (Trichuris vulpis) attaches to and irritates the lining of the large intestine and caecum, causing chronic or intermittent blood-streaked diarrhoea rather than the sudden severe episodes seen with infection, while hookworm, seen less often in the UK, feeds from the small intestine and is more likely to cause anaemia and dark, tarry stools than fresh blood. Dogs with regular access to parks or shared outdoor spaces are more frequently exposed, as whipworm eggs persist in soil for long periods. Weight loss and a fluctuating appetite often accompany the diarrhoea when parasite burden is high.
Dietary Indiscretion And Acute Gastroenteritis
A sudden change of food, fatty scraps, or scavenged material can irritate the intestinal lining enough to cause transient blood streaking in an otherwise formed or loose stool. This is one of the more common and self-limiting explanations, particularly in dogs known to raid bins or eat items found on walks, and it typically settles within a few days without other systemic signs. It is distinguished from acute haemorrhagic diarrhoea syndrome by the comparatively mild, non-jelly-like appearance of the stool and preserved energy levels.
Coagulopathy And Toxin-Related Bleeding
Anticoagulant rodenticide ingestion, or an overdose of anti-inflammatory medication such as ibuprofen, can impair clotting or damage the gut lining directly, leading to visible blood in the stool alongside other signs of bleeding elsewhere, such as bruising or bleeding gums. This differs from infectious causes in that the bleeding tendency is not confined to the gut. Dogs with access to garden sheds, farmland, or human medication cabinets carry some background risk.
Why timing matters
Early observation
Early recognition allows prompt assessment and intervention if needed.
Later presentation
Persistent or worsening signs may indicate progression requiring attention.
The significance of this symptom depends on its context, duration, and associated findings.
Conditions commonly associated
Canine Parvovirus
Parvovirus destroys the intestinal lining, causing characteristic profuse, bloody, foul-smelling diarrhoea.
Exocrine Pancreatic Insufficiency (EPI)
Undigested food and fat create loose, voluminous stools characteristic of malabsorption.
Campylobacteriosis
In more severe cases, particularly in young animals, Campylobacter can cause diarrhoea streaked with fresh blood or mucus.
Ibuprofen Toxicity
Loss of the intestinal lining's normal protection allows ulceration and bleeding that can appear as blood mixed through loose stool.
Intestinal Intussusception
Blood or mucus in the stool, sometimes described as redcurrant-jelly in appearance, develops as the telescoped bowel becomes congested and its lining sheds.
Salmonellosis
Blood-streaked, watery stools can appear when this bacterial infection inflames and damages the lining of the intestine.
Tritrichomonas Foetus in Cats
Inflammation of the colon lining from this infection can cause streaks of fresh blood or mucus to appear in the stool.
When to explore further
When the symptom is persistent or worsening
When other signs are present alongside
When daily activities or quality of life are affected
When there is uncertainty about the cause
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS