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What are Passing Black Stools?

It is vital to be aware of the consistency and color of your pet’s feces for the sake of his health. While your dog cannot tell us verbally what is wrong with him, by being observant, you can read the tell-tale signs if a health issue arises. If your dog has started passing black tarry stools, then it indicates the presence of digested blood in the feces, known as melena. For the stool to appear black, there must be a significant amount of bleeding into the stomach or small intestines. Note that bleeding into the colon or rectum (hematochezia) appears as fresh blood in the stool. Any amount of internal bleeding is a serious concern. The passing of black stools could occur due to any of the following conditions: 

  • Injury to your dog’s digestive system
  • Infectious agents 
  • Hemorrhagic gastroenteritis 
  • Gastrointestinal ulceration 
  • Cancer

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Why Passing Black Stools Occurs in Dogs

Injury to your Dog’s Digestive System 

A black, tarry stool (often very smelly) indicates that there is old blood somewhere in your dog’s digestive system, and internal bleeding is a concern. It may stem from an injury to the GI tract from the indiscriminate eating that some dogs are famous for, such as the ingestion of sharp twigs, parts of toys, and other random items.

Infectious Agents 

Intestinal disorders such as intestinal parasites, bacterial, viral, or fungal infections need to be ruled out as the cause. Any of these agents can cause internal bleeding within the stomach or small intestine as the parasite burrows into the lining of the organs. If they are the cause of the black stools due to internal bleeding, then treatment will be initiated to correct this condition. Needless to say, it needs a specialist’s intervention and care. 

Hemorrhagic Gastroenteritis

While the cause of hemorrhagic gastroenteritis is unknown, it needs immediate treatment to prevent your dog from dehydration and to prevent death; it is a very serious condition. The diagnosis is likely to be confirmed with a blood test. If your dog has this condition, the tests will reveal elevated packed cell volume levels (PCV). 

Gastrointestinal Ulceration 

If your dog is experiencing this condition, it can be caused by one of the three most common causes: hepatic (liver) disease, the use of non-steroidal anti-inflammatory drugs and neoplasia, which is the abnormal growth of cells. Your dog may show no other signs of discomfort, or they may experience a lack of appetite, weakness and pain in their abdomen. There are many causes for this condition, and it needs instant attention from a veterinarian.


No one wants their beloved dog to be diagnosed with cancer, but unfortunately, it can happen. It is common knowledge that the sooner cancer is found, the better chances of treatment and extending your dog’s life. While the passing of black stools does not necessarily indicate cancer, the quicker you can have it checked by a veterinarian the better for your dog. Observing your dog and noticing any symptoms is important, so if your dog has behavioral changes, lethargy, loss of appetite, unusual weight loss, and unusual odors, then it is advisable to get them to the clinic for a few diagnostic tests.

What to do if your Dog is Passing Black Stools

The first thing to do is to take your dog for an immediate physical examination with your veterinarian as black stools are an indication that all is not right. If you can take a sample of the stool to show the specialist, it may help in the diagnosis. Treatment and cost are determined as to the illness that your dog may be experiencing. 

If your dog has eaten something that is causing the internal bleeding (due to a sharp or pointed object), it may be that your dog needs surgery to remove the offending object. Your pet may need a few days in the hospital after the operation but should recover quickly and just require a course of antibiotics, rest and care once home. 

In the case that your dog is suffering an infectious condition or is battling with parasites and bacteria, a course of the appropriate medication will help overcome it. Often, your dog will have a follow up examination and tests to determine if the medications have been effective. 

For hemorrhagic gastroenteritis, it can be a problem to find the exact cause of the problem. To diagnose the ailment, your dog will require x-rays and blood tests. But if these tests do not help confirm what the problem is, then a biopsy may need to be done. The biopsy can be done via an endoscopy, or a biopsy can be surgical. These samples can help determine the treatment. 

As dogs mature they can be prone to some form of cancer, and it depends on the type of cancer as to how much your dog will be affected health wise. Your veterinarian will do blood tests, x-rays, and a complete physical examination of your dog to determine the extent of the damage.

If your dog is suffering from gastric ulcers, you veterinarian will look at rehydration and fluids depending on the severity of the condition. Dietary changes require a soft, bland diet that is easy to digest, allowing healing to occur. A urinalysis can help detect the virus, and blood work will be done to allow an accurate diagnosis.

Prevention of Passing Black Stools

While it is hard to prevent every disease or condition that your dog may get,  a good management program covering their health will help. Removing sticks and hard toys that they chew on can prevent any accidents with swallowing sharp pieces. A healthy diet is still the best prevention measure to practice. Speak with your veterinarian to see what is best for your dog. Usually, a wide variety of food that is close as possible to its natural state is best. Keeping your dog fit and just below the average weight is better for their health. Some dogs are better with three small meals rather than one large one, as it minimises the risk of bloating, which can be a dangerous condition.

Cost of Passing Black Stools

Treatment costs can vary considerably depending on the nature of the illness and what needs to be done to help correct it. Dogs are natural born scavengers and can cause internal injury by eating something that is either sharp or indigestible. The expense for removal of a foreign body and follow-up treatment can average $2500. Bacterial infections can cost on average $1,600. Hemorrhagic gastroenteritis costs from $2000 upwards depending on the severity. Gastrointestinal ulceration can cost up to $2200 for treatment. Cancers can cost $2000 and more. The cost is always related to the degree of the treatment required.