Blood in a dog's stool
A small streak of fresh blood with otherwise normal stools and a bright dog can be monitored briefly; black tarry stool, large blood volumes, or any unwell dog needs same-day vet contact.
Recognise the signs
- Fresh red blood streaked on or coating stool — usually large bowel origin
- Black, tarry, foul-smelling stool (melaena) — digested blood, upper gut origin
- Jelly-like mucus with blood — colitis pattern
- Large volumes of bloody, watery diarrhoea — possible HGE, true emergency
- Vomiting, lethargy, pale gums alongside bloody stool
First aid steps
- Photograph the stool — vets find this genuinely useful.
- Note frequency, volume, and any blood colour change.
- Withhold food for 4–6 hours, offer small amounts of water.
- Reintroduce a bland diet (boiled chicken and rice) if dog is bright and drinking.
- If signs are mild and resolving, recheck after 24 hours.
- If signs are worsening, vomiting joins, or any concerning sign appears — phone the vet.
Do NOT
- Do not give human anti-diarrhoeals (Imodium, Pepto-Bismol) without vet advice.
- Do not assume small blood streaks always mean nothing — recheck within 24 hours.
- Do not feed fatty food, mince, or cooked bones to 'settle the stomach'.
- Do not delay if there is any suspicion of rodenticide ingestion.
When to phone the vet immediately
- Black, tarry stools (digested blood)
- Large volumes of bloody, watery diarrhoea — possible HGE
- Pale gums, lethargy, collapse
- Vomiting alongside bloody stool
- Known or suspected rodenticide access
- Puppy under 6 months, senior dog, or any dog with chronic illness
- Persistent blood beyond 48 hours
Signs that can usually wait for a routine appointment
- A single small streak of fresh blood on otherwise formed stool, in a bright, eating, drinking, playful dog with no other signs, can usually be monitored at home for 24 hours.
Common causes
- Dietary indiscretion — scavenged food, sudden diet change
- Stress colitis (especially after kennelling, travel, or new home)
- Worms or other parasites
- Inflammatory bowel disease
- Bacterial infection (Campylobacter, Salmonella)
- Haemorrhagic gastroenteritis (HGE) — sudden severe bloody diarrhoea, can be life-threatening
- Foreign body, polyp, or tumour
- Anal gland problems
- Rodenticide poisoning (warfarin-type) — bleeding in many places
What the vet will need to know
- Frequency and volume of stools and blood
- Colour — fresh red versus black tarry
- Other signs — vomiting, appetite, drinking
- Recent diet changes, scavenging, or new treats
- Possible toxin or rodenticide access
- Worming and vaccination status
- Photo of the stool
Aftercare
- Bland diet for 3–5 days, gradual return to normal food.
- Probiotic paste from the vet often helps.
- Worming treatment if not recent.
- Repeat stool sample in 7–10 days if infection was suspected.
- Investigate persistent or recurring cases — bloodwork, ultrasound, endoscopy may be needed.
Prevention
- Bin-proof kitchens; supervise off-lead walks for scavenging.
- Transition diets over 5–7 days.
- Stay current on worming.
- Manage stress at known trigger points (kennelling, fireworks, moves).
- Secure rodenticide in tamper-proof bait stations only.
Breed-specific notes
- Small breeds (Yorkshire Terrier, Maltese, Schnauzer) appear over-represented in HGE.
- German Shepherds and Boxers higher incidence of inflammatory bowel disease.
Frequently asked questions
What does black tarry stool mean?
Black, tar-like stools (melaena) indicate digested blood from the stomach or upper gut — upper GI bleeding. This always warrants vet investigation, often urgent depending on quantity and the dog's condition. Iron supplements, bismuth medication and some foods can darken stools too, but black tar-like consistency should never be assumed harmless.
What is HGE and why is it serious?
Haemorrhagic gastroenteritis (now often called acute haemorrhagic diarrhoea syndrome, AHDS) is a sudden severe bloody diarrhoea, sometimes with vomiting. The classic appearance is 'raspberry jam' diarrhoea. It can cause rapid dehydration and shock and needs prompt IV fluids and supportive care — phone the vet immediately.
Could blood in stool just be from licking too much?
Anal licking and gland issues can cause small streaks of blood that come from outside the anus rather than the gut. A vet check identifies the source and rules out gut causes.