No Fun at All: Long-Term Diarrhea in Dogs and Cats

Don’t ignore your pet’s prolonged potty issues.

Parasites and food allergies are just 2 of the many culprits behind long-term diarrhea in animals. By: marczero1980

Diarrhea is a symptom rather than a condition in its own right.

So when it comes to treating such cases, getting to the, er, bottom of things to find the underlying cause is crucial.

Bizarrely, I like investigating long-term diarrhea cases — it gives me a great deal of satisfaction because by finding the cause and treating it, I can improve both the pet’s and human’s quality of life.


Signs of diarrhea are self-explanatory: loose or liquid motions rather than a nice, firm, sausage-shaped stool. Put simply: If you can’t pick it up easily, then it’s diarrhea.

If your dog has diarrhea, a quick plea from a veterinarian — take a look. It really helps to know if blood or mucus is present.

If you are really keen, there is even a Bristol stool chart that ranks feces on a scale from 1 to 7 for consistency (1 is rock-hard nuggets; 7 is completely liquid), which is all valuable information when it comes to deciding on the best course of treatment.


The causes of diarrhea are many and varied.


  • Food allergy or sensitivity
  • Bacterial infections (salmonella, campylobacter, etc.)
  • Parasites (worms, giardia, coccidian)
  • Inflammatory bowel disease (IBD)
  • Small intestinal bacterial overgrowth (SIBO)
  • Low cobalamin (Vitamin B) levels in the bowel wall
  • Lymphoma (bowel cancer, which is more likely in the cat)
  • Protein-losing enteropathy (PLE)
  • Eosinophilic enteritis

Disease outside the bowel:

  • Exocrine pancreatic insufficiency (EPI)
  • Low protein levels in the blood
  • Pancreatitis
  • Liver disease
  • Severe heart failure
  • Stress
If your pet’s loose stool doesn’t improve after a few days, see the vet — the cause may be more serious than you think. By: eiriknewth


There are so many causes of diarrhea that investigation requires a logical approach. Your vet will take a detailed history and an account of the pet’s age and breed, recent changes of diet and contact with infectious agents.

If a puppy has long-term diarrhea, the immediate suspect may be a parasitic infection, and the most useful diagnostic test is fecal analysis. By looking for parasites, eggs and larvae under the microscope, sometimes a diagnosis is made, and appropriate treatment is started swiftly.

Adult animals with diarrhea fall into 2 groups:

  1. Self-limiting cases that get better in a few days
  2. Those with long-term diarrhea

Long-term diarrhea tends not to be straightforward, and a screening blood test may help rule out disease that is causing it.

If the panel and fecal analysis are normal, then next on the list is a blood test looking at bowel function. This checks that the pancreas is producing enough digestive enzymes, the bowel is not deficient in cobalamin (essential for healthy digestion) and there is no overgrowth of bacteria within the bowel lumen.

If these tests draw a blank, then either an ultrasound scan or an endoscopy may be appropriate to reach a diagnosis. Ultimately, in hard-to-crack cases, a bowel biopsy should give a definitive answer, but this procedure is not without risk and should be discussed thoroughly with your vet first.


Key to treatment is identifying the reason for the diarrhea and addressing that issue.

These common conditions require the following treatments:

  • Food allergy: Hypoallergenic diet
  • Parasite infection: Fenbendazole (depending on the parasite)
  • SIBO: A corrective course of antibiotics
  • EPI: Supplement the pancreatic enzymes
  • IBD: Anti-inflammatory drugs, low-allergen diet
  • Lymphoma: Surgery and possibly chemotherapy


To prevent long-term diarrhea, seeking veterinary advice in the early stages is key. When ignored, a short-term tummy upset can become a long-term problem if the bowel’s natural balance becomes disturbed and its ability to digest food is knocked out of whack.

So if simple diarrhea doesn’t settle after a couple of days of a light diet, take your pet to the veterinarian to get checked out.


  • Small Animal Internal Medicine. Nelson & Couto. Publisher: Mosby. 3rd edition.


This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 11, 2018.

Dr. Pippa Elliott, BVMS, MRCVS

View posts by Dr. Pippa Elliott, BVMS, MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty puggle called Poggle, 3 cats and a bearded dragon.

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