What Is the Cause of Dark Bloody Mucous in a Dog's Stool?

Updated February 21, 2017

As a dog owner, the sight of dark bloody mucus in your dog's stool can be quite alarming. When there is digested blood in a dog's faeces the stool will appear black and tarry, this is called melena. The presence of dark red blood may indicate bleeding in the dog's gastrointestinal tract.

Possible Causes

There are many possible causes of melena. A very common cause is an ulcer. Signs that a dog may have a stomach ulcer will not only include dark red blood in the stool but also vomiting, loss of appetite and weakness.

Other causes of melena are; cancer, the presence of a foreign body in the stomach or intestinal tract, some bleeding disorders, or a haemorrhage within the intestinal tract.

Signs to Watch For

If you notice dark red blood in your dog's stool, look for these other signs which indicate that there could be a serious problem:

  • If the stools are so dark they appear almost black
  • Drinking excessively, which could lead to more frequent urination
  • Loss of appetite or a decrease in appetite, which will lead to weight loss
  • Diarrhoea
  • Vomiting

What to Do Next

Calling a veterinarian and scheduling an immediate appointment is definitely the next step, should your dog exhibit the above signs and symptoms of a problem.

What to Consider

To figure out what contributed to the presence of melena in a dog's stool, give in depth consideration to what the dog may have done in the days prior to exhibiting signs that there is a problem.

  • Was the dog playing with any small children's toys that they could have swallowed?
  • Was the dog chewing apart one of it's own toys in which they may have swallowed a piece of the toy?
  • Has the dog been on any medication that could have caused it to get an ulcer? Some anti-inflammatory medications can cause ulcers in dogs.
  • Does the dog have a history of tumours?

All of the above need to be considered and talked over with the veterinarian so they may be able to begin ruling out causes.

Possible Treatments

Of course, only a veterinarian should give out an itinerary of treatment. However, here are some common ways melena is treated:

  • Feeding a bland diet
  • Avoiding certain medications that may irritate the gastrointestinal tract
  • In some cases, medications that block the production of stomach acid and actually coat the stomach itself may be prescribed
  • Depending on the reason for the presence of melena, surgery and/or hospitalisation may be required.


If you suspect your dog may have eaten something that is blocking their digestive tract, it is imperative that you have them seen by a veterinarian as soon as possible.

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