We do come up with the loveliest topics for articles, don’t we? Although today’s question is a little disgusting, it is also an important one. All responsible dog owners pick up their pet’s poop, so you tend to get a good idea of what their faeces normally looks like. This is why it may be a shock if one day it looks red! What does this mean? Should you be concerned? Why is my dog’s poo red?

What colour should dog poo be anyway?

Most dogs, and indeed most mammals, have a lovely chocolate-brown colour poo. The reason for this is due to a substance called bilirubin. Bilirubin is produced when the liver breaks down old red blood cells. Bilirubin is toxic in high quantities, so it is excreted in bile when an animal eats. The pigments in bilirubin stain faeces brown.

However, healthy poo can also vary in colour quite considerably, from yellow to brown to tan to green. It depends a lot on what dogs eat as well as individual biology. The main thing to look out for is consistency. If your dog’s poo is consistently one colour and they are otherwise healthy, it is likely normal.

In earlier decades, it was not uncommon to see white dog poo left behind on the pavement. While the poo itself reflects the less than appropriate hygiene standards of the time, the colour was generally due to dogs’ diets at the time. Dog food back then was of a much lower quality and often bulked out with bone meal. The calcium in bone meal was mostly indigestible, so stained the poo white as it came out. Interestingly, we are seeing a slight resurgence of white poo as more people are feeding raw food diets to dogs, which often includes the bones. As well as the risks associated with raw food in general, the bones can cause damage if they get stuck, so we don’t usually recommend this.

So why is my dog’s poo red?

The main reason why your dog’s poo is red is probably due to blood. Blood in poo can be fresh red blood, or it can be dark red, brown or even black. It can be present just on the outside of the stool, or throughout. The blood can be just at the start of the faeces, the end or covering the whole thing. Blood in the stools is often seen alongside diarrhoea, but not always.

It is helpful to determine where the blood has come from by its appearance. Bright red fresh blood likely originates from the large intestines, rectum or anus. This is because the blood has not had a chance to be digested. This is called haematochezia.

Dark red, brown or even black blood originates from higher up, often the small intestines. The blood has had time to pass through the digestive tract and be broken down, resulting in a darker colour. This is called melaena. Melaena can also occur due to bleeding in the stomach, oesophagus, mouth and even the lungs if it is coughed up and swallowed.

What causes blood in poo?

There are a huge number of reasons why your dog has blood in its poo; so we will list some of them below. Remember that although it is shocking, seeing blood in your dog’s poo isn’t necessarily an emergency. But it is always best to at least ring up your vets to describe the stool and ask if you need to come in. And, of course, if your dog has other signs such as diarrhoea or vomiting, then definitely see your vet ASAP.

Stress and Inflammation

Just like in people, stress can result in increased inflammation which can cause damage and bleeding to the wall of the intestines, resulting in blood in the stools. Dogs can, of course, be stressed for many reasons. For example, sometimes we see a little blood in the stools of dogs stressed in hospital.

Inflammation can also be the primary reason for bloody poo. Almost all of the diseases listed below can cause inflammation and bloody stools. Some of the most common are worms, infection, blockages and masses. Often inflammation results in pain when going to the toilet, especially if the inflammation is in the rectum or anus. Chronic enteropathies (gastrointestinal disease) is also another common cause.


Certain drugs can cause bloody faeces, either as a side effect of normal use or because they are toxic. Two of the most common are non-steroidal drugs (NSAIDs) and steroids – these drugs inhibit prostaglandins to reduce inflammation, so are great for general pain or discomfort. However, prostaglandins are also responsible for maintaining the wall of the stomach – inhibiting prostaglandins can leave the stomach unprotected from its own acid, resulting in ulcers and bleeding. We can minimise this risk by avoiding their use with gastrointestinal disease, ensuring doses are correct, never using NSAIDs and steroids together, and providing antacid drugs alongside. If your dog has been prescribed either of these and you notice vomiting, diarrhoea or bloody poo, stop using them and contact your vet.

Other drugs are particularly prone to causing damage to the stomach and bleeding, in particular human aspirin and ibuprofen, through similar mechanisms to canine NSAIDs. Even small doses of these drugs can cause GI upset, bloody stools as well as other more serious issues like liver or kidney failure. Never use these in dogs and keep them well out of their reach.


Lots of things can get stuck and cause blockages in dogs’ intestines, ranging from food and sticks to toys and trash. As well as causing discomfort and constipation, a dog squeezing hard past a partial blockage can cause bleeding from the intestines. Dogs with stuck foreign bodies should be seen as an emergency as they may need surgery – blood from the back end is a good early warning sign. Constipation itself can cause inflammation as the poo stops moving, dries out and becomes painful to push against. The longer it sits in the intestines, the more dried out and difficult to remove it gets.

Other things can cause blockages in the intestines which results in pressure, inflammation and bleeding. One very common blockage in non-castrated dogs is the prostate – high levels of testosterone can cause growth of the prostate to the point it starts to block the rectum, causing pain and bleeding. It can be treated with drugs though castration will stop it recurring. Prostate enlargement is one of the main reasons we often recommend castration. Dogs can also get masses growing in the intestines, which can cause full or partial blockage – older dogs are especially vulnerable to this.


Many infections cause inflammation and bleeding in the intestines. Often dogs will have a high temperature, may be lethargic or even vomit as well. Young and old dogs are more vulnerable due to their reduced immune systems, as well as animals in dirty environments like puppy farms.

Salmonella and Campylobacter are two common GI infections related to food. Both tend to cause diarrhoea and dehydration. The biggest consideration with these two is that they are zoonotic so there is a risk of a sick dog spreading them to humans if there isn’t decent hygiene. We know that the risk of these infections are also increased in raw fed dogs as the bacteria are not killed by cooking– people who are vulnerable to infection, such as children, the elderly or immunocompromised, should not have raw fed dogs in the house. Luckily, these diseases are often self-limiting or easily treated with antibiotics in dogs.

One of the most serious infections that causes severe bloody diarrhoea is parvovirus, most common in puppies. This virus inhabits the intestinal cells, causing profuse diarrhoea. These puppies often end up on death’s door fighting the disease. There is no specific treatment for parvovirus, just symptomatic therapy – even with intense hospitalisation, some will die. We can prevent parvovirus with regular vaccinations, particularly when young. Avoid letting your puppy interact with other dogs until they are fully vaccinated. There is a similar disease called haemorrhagic gastroenteritis that looks very similar to parvovirus, but is not caused by infection. It is managed and treated the same way, and can be just as dangerous.


There are plenty of worms that infect dogs, particularly puppies, and can cause back-end bleeding. Some even latch onto the intestine walls and cause damage this way. In severe burdens, dogs can get quite malnourished or anaemic. Luckily, they are generally easily treatable with worming tablets, and regular treatment will prevent the majority of infections. Always get your dog wormed regularly, especially when young.

Bleeding Disorders

There are several bleeding disorders that can cause increased risk of blood from the back end. Most are thankfully not common but should be a consideration for melaena or haematochezia. They also cause extensive bleeding from other places, such as the mouth, eyes, nose, skin and wounds.

Some rare genetic diseases, like haemophilia, result in a problem with the clotting system in dogs. Where a normal dog that bleeds forms a clot quickly, preventing significant blood loss, a dog with one of these diseases cannot form proper clots, causing uncontrolled bleeding. In the intestines, any damage from foreign bodies or inflammation can result in more bleeding than expected. Many of these diseases are difficult to diagnose and treat or manage.

Thrombocytes are platelets, the first factor in forming clots when there is damage. A low platelet count is called thrombocytopaenia (TP) – TP can has several causes, including infections, liver disease, bone marrow disease, cancer and even non-specific chronic disease. We can diagnose TP by measuring the number of thrombocytes in blood – depending on the cause, we may be able to restore platelet levels. Serious TP may require a blood transfusion to prevent uncontrolled bleeding.


Dogs that have been poisoned by warfarin (or its cousins, the coumarins – the most common ingredients in rat poison) often have uncontrolled bleeding, including from the back end. These drugs act as anti-coagulants so they prevent clots from forming in the body. Bleeding is not always obvious and can start a few days after ingestion. Dogs with warfarin toxicity need to be seen by a vet immediately, and handled with care to avoid causing damage and bleeding. We can treat the toxicity with hospitalisation, fluid therapy, vitamin K and blood transfusions, depending on the degree of toxicity. Always be wary of visiting places where someone may have put down rat bait, such as farms.

Problems in the mouth, stomach, throat or lungs

As we mentioned above, bleeding can occur higher up in the GI tract, or even in the lungs,  resulting in blood being swallowed and excreted in faeces as melaena. There are many causes of bleeding from these areas. Some common ones include dental disease, trauma to the face, stomach ulcers, severe vomiting causing oesophageal damage, pneumonia, kennel cough and cancers. A thorough clinical exam by your vet may help narrow down the causes of bleeding to these areas.

How vets diagnose causes of blood in poo

Again, this is highly variable, and will depend on the vet, the client, the dog and lots of other factors. Sometimes, we don’t even need to fully diagnose a problem to treat it, and symptomatic treatment is enough.

We always start by taking a history of the problem, asking questions like when did it start, how much blood, how often, any discomfort, any vomiting, any diarrhoea, any anorexia, and so on. We then perform a clinical exam, where we examine your dog from nose to tail, focussing particularly on their hydration status, demeanour, heart and respiratory rate, abdominal discomfort, temperature and more. Sometimes, this is enough for a presumptive diagnosis and for treatment to be given, particularly for mild cases of bloody stools.

If you or we are concerned, or symptomatic treatment has not worked, a sensible next step is to take a general blood sample. This can give us clues to any signs of infection or inflammation, anaemia or dehydration, signs of organ dysfunction, electrolyte abnormalities and more. More specific blood tests can identify pancreatitis, liver disease, kidney disease, problems with coagulation, specific infectious diseases, and so on.

From here, there are other tests, depending on the dog

Faecal sampling can show if there are parasites, bacteria or viruses present, while urine testing is sometimes useful if we are concerned the urinary system is involved, or to check kidney function.

Finally, there are different sorts of imaging

Abdominal ultrasound can show us the structure of organs in your dog’s belly, and could identify a blockage. X-rays can identify blockages too, as well as organ size – some objects, such as stuck bones, even show up on x-ray. More advanced imaging like CT or MRI show even greater resolution of the body. We can even use endoscopy to look inside your dog, to identify masses, sites of infection or take samples via biopsy. In extreme cases, exploratory surgery may be sensible to look at the organs up close.

Whether a quick fix that only needs symptomatic treatment, to serious conditions that need a lot of diagnostic techniques and treatments, blood in the stools is not normal. If you spot any haematochezia or melaena in your dog’s faeces, at least contact your vet to discuss if a visit is sensible.

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