PET42 guide
Blood in dog stools: colours, causes and warning signs
Red blood and black, tarry stools may indicate different bleeding sites. Recognise warning signs and prepare useful information for your vet.
Fresh red blood and black, tarry stools look different and can indicate different bleeding sites. Both should be taken seriously.
Red or black makes a difference
Bright red blood often comes from the lower intestine or the rectal and anal area. It may appear as streaks on the stool or be mixed with mucus. Black, shiny, tarry stools are called melaena. They may contain digested blood from the stomach, small intestine, mouth or airways and are particularly urgent.
Colour alone does not provide a diagnosis. Red foods, dyes, soil or certain medicines can change the appearance. A photo in good light and a fresh stool sample help your vet.
Possible causes
Possible triggers include inflammation, parasites, infections, food changes, foreign bodies, injuries, ulcers, clotting disorders, poisoning and tumours. In puppies, serious infections must also be considered. After possible rat poison ingestion, blood in the stool may reflect a clotting disorder.
These warning signs are an emergency
Immediate veterinary help is needed for:
- Black, tarry stools
- Larger amounts of blood or repeated bloody diarrhoea
- Pale mucous membranes
- Weakness, collapse or rapid breathing
- Vomiting at the same time
- Severe abdominal pain or a bloated abdomen
- Possible ingestion of poison or a foreign body
- Blood in the stool of puppies or dogs with serious underlying illnesses
Even smaller amounts should be assessed promptly if they recur, your dog loses weight, eats less or changes behaviour.
What to record for the appointment
Record colour, amount, consistency and frequency. Note food, treats, medication, possible rubbish or objects, parasite prevention and changes over the past few days. If possible, bring a fresh stool sample in a clean container.
Do not give diarrhoea medication or painkillers from your medicine cabinet. Some are unsuitable for dogs; others can worsen bleeding or mask important symptoms. A homemade bland diet may sometimes form part of a veterinary plan for mild symptoms, but is not suitable for every cause.
Review feeding systematically
Once acute and organic causes have been ruled out, a food diary can help. Record main food, chews, training treats and table scraps alongside stool quality and symptoms. This is the only way to identify whether a change actually relates to the diet.
A common mistake is changing several ingredients, supplements and foods at once. This makes the response almost impossible to assess. A clear plan agreed with your vet and, if necessary, a nutrition adviser is better.
Note: black stools, heavy bleeding, weakness or pale mucous membranes require immediate veterinary help.
Sources
- Reference: Cornell University College of Veterinary Medicine: Diarrhea
- Reference: MSD Veterinary Manual: Disorders of the Stomach and Intestines in Dogs
- Reference: Cornell University College of Veterinary Medicine: Canine Parvovirus
Advice tailored to your dog
Review your dog’s individual diet
Take the independent PET42 food check now: we assess labelling, daily amounts and possible feeding problems. Blood in the stool must first be evaluated by a vet.
Questionnaire, checkout and feeding advice are provided in German.
