Why Does My Dog Have Diarrhea: 5 Causes of Diarrhea in Dogs

Why Does My Dog Have Diarrhea

If you are a dog parent, you have probably faced the issue of diarrhea in your dog at least once. It is common in animals, but it can have a lot of different reasons. Some of those reasons are easy to be fixed, but others are very serious. 

What is Considerate Diarrhea in Dogs? 

Diarrhea is the increase in the volume, fluidity, and frequency of your dog’s feces. Other characteristics can be taken into consideration, like the color, the content, and, more importantly, the duration. 

  • If diarrhea lasts less than 2 weeks, it is considered acute diarrhea in dogs.
  • If diarrhea lasts more than 2 weeks, it is considered chronic diarrhea in dogs.

What Other Signs Come With Diarrhea? 

Diarrhea is considered a primary sign of intestinal dysfunction, but it is rarely the only sign of sickness your dog will be showing. Your dog will usually exhibit other secondary clinical signs that can be very important and help with the diagnosis.

The secondary signs your dog might show are dehydration, vomiting, weight loss, abdominal pain, bad breath, polydipsia (increased water consumption), and fever.

If you are wondering why my dog has diarrhea, you will find a lot of reasons like dietary issues, inflammation, infections, obstruction, and many more. To be able to diagnose it properly, you will need to take your dog to the vet, who will run the tests needed. 

Physiology of Diarrhea

Diarrhea is the result of increased secretion of water and electrolytes or decreased absorption of water and electrolytes in the gastrointestinal tract. There can be different types of diarrhea, but two of them are major: osmotic diarrhea and secretory diarrhea

Osmotic Diarrhea

Osmotic diarrhea is caused by excessive amounts of osmotically active solutes in the intestinal lumen. These active solutes are poorly absorbed by the gastrointestinal tract. 

In the cases of malabsorptive disorders, nutrients are not absorbed or digested right and remain in large amounts in the intestine, attracting water by osmosis. This malabsorption won’t only lead to an increase in water, but it will harm the intestinal microflora as well.

An example of osmotic diarrhea: is exocrine pancreatic insufficiency. 

Secretory Diarrhea

Secretory diarrhea in dogs is the result of an abnormal electrolyte transport caused by a decreased absorption of ions. It is caused mainly by either viral or bacterial infections, a genetic disorder, or some types of drugs.

Examples of secretory diarrhea are Escherichia Coli (bacteria) and inflammatory bowel disease (chronic inflammation in the gastrointestinal tract).

Why Does My Dog Have Diarrhea?

There’s a pretty big list of what might be causing diarrhea in your dog. This is why you should take your furry friend to the veterinarian, who should run tests to diagnose the cause. 

These causes can be dietary, inflammatory, infectious, extraintestinal disorders, and mechanical disorders. Even if it might seem like it’s not a huge deal, you should know that sometimes diarrhea can be a consequence of a life-threatening condition, and you cannot ignore it. 

1. Dietary

A change in your dog’s diet will cause an inflammatory response because their gastrointestinal enzymes are not used to the new food (either toxic or not), which will lead to acute diarrhea. 

How can a diet cause diarrhea in dogs?

  • Non-balanced or nonsafe homemade.
  • A sudden change of diet.
  • Eating from the garbage or feces or even dead animals.
  • Eating toxic food for dogs.
  • Overeating.
  • Food allergies (mostly chicken).

2. Inflammatory

Another reason for diarrhea is inflammation. Inflammation is a normal response of the body against infection or injury, but it can become chronic. The mucosa of the intestine can become inflamed and disrupted. 

Some inflammatory diseases that cause diarrhea:

  • Inflammatory bowel disease, either Crohn’s disease or ulcerative colitis
  • Antibiotic-responsive diarrhea, which means there’s an abnormal increase of bacteria in the intestine
  • Lymphangiectasia is caused by enlarged lymph vessels. It’s considered rare.
  • Hemorrhagic gastroenteritis (dog bloody diarrhea) occurs after overfeeding a new type of food.

3. Infectious

Diarrhea can also be caused by a parasitic, bacterial, or viral infection. These infections can be life-threatening and are one of the most dangerous causes of diarrhea.

  • Endoparasite is a primary concern in young dogs. Your puppy can even be born with worms. Two of the most common parasites are Toxocara Canis and Giardia. These two will not only cause diarrhea, but they will lead to anorexia and dehydration as well.
  • Bacterial infections are usually transmitted in raw meat and infected food. The most common bacterial infections are salmonella, clostridium perfringens, campylobacter, and E. coli.
  • Viral infections, like canine parvovirus, which is a very deadly virus that causes bloody diarrhea.
  • Fungal infections, like histoplasmosis, pythium, and cryptococcosis.

4. Extraintestinal Disorders

The main causes of diarrhea are gastrointestinal, but a lot of extraintestinal disorders can cause it as well.

  • Pancreatitis (inflammation of the pancreas). It can be triggered by a high-fat diet, obesity, trauma, or cancer. It is usually a very serious condition that needs urgent treatment.
  • Exocrine pancreatic insufficiency. In this condition, the pancreas is not secreting enough enzymes that help break down the nutrients.
  • Liver disease. The feces will look pale when your dog has a liver disease like cirrhosis.
  • Kidney disease. Dogs with ESKD (end-stage kidney disease) presented with diarrhea.
  • Hypoadrenocorticism. Dogs with this condition have impaired absorption of electrolytes and water in the intestine due to aldosterone( hormone) deficiency. 
  • Hyperthyroidism. Dogs with this condition have a decreased small bowel transit time that will lead to diarrhea.

5. Tumors 

Last but not least, what might be causing diarrhea to your dog can be a tumor. It can be either malignant( cancerous) or benign ( not cancerous).

Some types of tumors:

  • Apudomas (tumors that arise from the neuroendocrine system and occur in the gastrointestinal tract)
  • Neoplastic carcinoma (an abnormal growth, either cancerous or not, that spreads through the blood)
  • Leiomyosarcomas ( cancer that grows in the smooth muscle)
  • Mast cell tumors (masses that can occur in many body parts, including the intestine) 

Difference Between Acute and Chronic Diarrhea 

Acute Diarrhea

Diarrhea is called acute if it lasts less than 4 weeks. Mainly it is caused by a virus or change in the diet of the dog. Even stress can cause diarrhea. It can be caused by bacteria as well. If it lasts more than four weeks, this means the body is unable to get rid of the pathogen by itself.

Chronic Diarrhea

Diarrhea becomes chronic when it lasts more than 4 weeks. It can happen due to many reasons:

  • Malabsorption of the nutrients such as carbs and lactose.
  • Inflammatory bowel disease (IBD).
  • Medications such as antibiotics, anti-inflammatory, and antiemetic. 
  • Cancerous or noncancerous tumors in the colon.
  • Parasitic infection.
  • Diabetes.
  • Irritable bowel syndrome (IBS).

When to Take a Dog to Vet for Diarrhea?

Sometimes the cause of diarrhea can be very simple, and it resolves by itself, like in the case of stress. Do not panic, and run to the vet immediately if your dog has diarrhea. If one or more of the following points are happening with your dog, then please contact your veterinarian:

  • Presence of blood in the feces.
  • Your dog has had diarrhea for more than 2days but is acting fine.
  • Your dog has other symptoms of diarrhea, such as vomiting and fever.
  • Presence of worms in diarrhea.
  • Your dog keeps having diarrhea every few weeks.

How is Diarrhea Treated? 

In order to treat diarrhea, you need to know what’s causing it. Your veterinarian will start with a physical examination and will learn about the history of your dog, including their diet, their last internal parasite treatment, their last vaccine, if they have any medical history and other questions that will help them with the diagnosis. 

Then they will proceed to run blood and fecal tests to have a final diagnosis. Upon this, your veterinarian will prescribe the best treatment for your dog.

Nutritional Management

If a dietary change or food allergy is the reason why your dog has diarrhea, the best treatment is nutritional management. Your vet will prescribe sensitive, dry food free of allergens for your dog. 

Switching to gastrointestinal food is very beneficial as well, even if the main cause of diarrhea is not food. Some veterinarians suggest switching to a homemade diet, including only boiled chicken and rice. But new studies have shown that this homemade diet lacks a lot of nutrients which lead eventually to more problems. This is why the best option is switching to gastrointestinal dry food or/and wet food.


If the reason why your dog is having diarrhea is an infection, mostly bacterial or protozoan (giardia), your veterinarian will prescribe an antibiotic that best suits that type of infection. In cases of viral infections, such as canine parvovirus, an antibiotic is needed to prevent secondary bacterial infections.

Keep in Mind :

Never use antibiotics for your pet on your own. It should be prescribed by a veterinarian.

woman giving capsule to a dog
Image credit: New Africa, Shutterstock

Supportive Therapy

Supportive therapy is needed if the diarrhea is severe and leads to dehydration and other symptoms. The supportive therapy can include iv fluids to help rehydrate your dog, antiemetics, and anti-inflammatory depending on the dog’s symptoms.


Probiotics are good microorganisms that are very recommended to you in case of diarrhea. Usually, it is administered as a supplement that supports the intestinal microflora and helps to stop diarrhea and prevents more damage.

Internal Parasite Treatment 

If your dog is not dewormed, and/or eats raw food, or hunts rodents, it will probably have intestinal parasites. These parasites are a very common cause of diarrhea, and your dog should be treated for them at least every 3-4 months (depending on your dog’s environment). 

Usually, your vet will start by doing a fecal test that shows if there are any parasites present in the intestine. If yes, they will prescribe an internal parasite treatment with a dose depending on your dog’s weight and condition. Supportive therapy is recommended as well to accelerate recovery.

How to Stop Dog Diarrhea?

The good news is that most of the causes can be prevented.

  • You can prevent viral infections such as canine parvovirus by vaccinating your dog. Unvaccinated dogs are prone to catching deadly diseases. It is very important to keep your dog away from the streets and from other dogs before finishing all of his vaccination.
  • You can prevent some bacterial infections by staying away from raw food and providing your dog with clean bowls and an environment. Dogs who eat raw meat are at a much higher risk of catching bacteria such as salmonella and E. coli, which are responsible for diarrhea.
  • Stay away from toxic foods and table scraps. Some of our food contains a lot of spices and fatty oils or even toxic food for dogs. 
  • Do not miss your dog’s internal parasite treatment every 3-4 weeks.
  • Hide the foods and medications that can harm your dog.
  • Feed good quality food.


The reason why your dog has diarrhea can range from simple anxiety or stress to something as big and dangerous as cancer or a deadly virus. It is important not to panic and try to find a reason that might have triggered it so you can help your veterinarian with the diagnosis. 

If you’re asking why my dog has diarrhea, only laboratory tests and a veterinary check can help answer your question, depending on your dog’s case.

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