By Dial A Vet Veterinary Team
Diarrhoea is one of the most common problems vets see in dogs. Most cases are short-lived and caused by something the dog ate, but diarrhoea can also be the first sign of parvovirus, poisoning, or a chronic gut condition. The details of the poo itself, how often it happens, and how your dog is acting all help a vet work out what is going on. This page explains the types and causes. If you need a practical plan for today, see my dog has diarrhoea: what to do in the first 24 to 48 hours.
Key takeaways
- Acute diarrhoea comes on suddenly and often settles within a few days. Chronic diarrhoea lasts more than two to three weeks or keeps coming back.
- Small bowel diarrhoea tends to be large in volume with weight loss. Large bowel diarrhoea tends to be frequent, small, urgent, and sometimes with mucus or fresh blood.
- Common causes include diet changes, scavenging, parasites, infections, stress, and medication side effects.
- Puppies, seniors, and dogs with other illness can become dehydrated quickly.
- Bloody or black diarrhoea, vomiting, lethargy, or a puppy with diarrhoea needs prompt veterinary attention.
Types of diarrhoea
Acute versus chronic. Acute diarrhoea starts suddenly and usually has a short-term trigger. Chronic diarrhoea persists for weeks or recurs, and points towards ongoing problems such as food sensitivities, inflammatory bowel disease, or problems with the pancreas. See long-term diarrhoea in dogs and cats.
Small bowel versus large bowel. Small bowel diarrhoea often means larger amounts of loose stool a few times a day, sometimes with weight loss, gas, or vomiting. Large bowel diarrhoea, or colitis, usually means many small, urgent poos, straining, mucus, and sometimes streaks of red blood. Telling your vet which pattern you see narrows the possibilities.
Common causes
- Diet. Sudden food changes, rich treats, table scraps, bin raiding, and food intolerance.
- Parasites. Roundworms, hookworms, whipworms, Giardia, and coccidia. See worms in dogs.
- Infections. Viruses such as parvovirus, and some bacteria. See infectious causes of diarrhoea in dogs and puppies.
- Stress. Boarding, travel, moving house, or new pets.
- Medications. Antibiotics and some other drugs can upset the gut.
- Toxins. Many poisons cause vomiting and diarrhoea.
- Other diseases. Pancreatitis, liver or kidney disease, Addison's disease, inflammatory bowel disease, and some cancers.
- Haemorrhagic gastroenteritis. A sudden, severe bloody diarrhoea. See HGE in dogs.
What to look at
Vets find it useful to know the colour, consistency, and frequency of the stools, whether there is mucus or blood, whether your dog is straining, and whether they are eating, drinking, and active. A photo of the stool is often very helpful, even if it feels awkward to take.
- Red streaks or jelly-like blood usually come from the large bowel. See blood in dog stool.
- Black, tarry stools can mean bleeding higher in the gut and are more concerning.
- Pale, greasy, or bulky stools can point to digestion problems.
When it is urgent
Go to an emergency veterinary hospital straight away if your dog:
- Has large amounts of bloody diarrhoea or black, tarry stools
- Is also vomiting repeatedly or cannot keep water down
- Is lethargic, weak, collapsing, or has pale or tacky gums
- Is a puppy, especially one not fully vaccinated (parvovirus can be fatal)
- Has a painful or swollen belly
- May have eaten a toxin or a foreign object
Book a vet visit within a day or so if diarrhoea lasts more than 24 to 48 hours, keeps returning, or your dog is losing weight.
How vets diagnose and treat diarrhoea
For a bright dog with mild, short-term diarrhoea, a vet may examine the dog, check a faecal sample for parasites, and suggest supportive care. If the dog is unwell or the diarrhoea is chronic, they may recommend blood tests, a parvovirus test in puppies, pancreas tests, imaging, food trials, or intestinal biopsies. Treatment depends on the cause and might include fluids, anti-nausea medication, deworming, a vet-recommended diet, fibre or probiotic products, or medication for specific conditions. Many cases of acute diarrhoea do not need antibiotics, and current guidelines encourage vets to reserve them for dogs with signs of serious infection.
Prevention
- Change diets slowly over about a week.
- Limit table scraps and secure bins.
- Keep up regular worming and vaccinations.
- Pick up and dispose of poo promptly to reduce reinfection with parasites.
- Plan for stress, such as boarding or travel, with familiar food and routines.
FAQ
How long does diarrhoea usually last in dogs?
Many mild cases settle within one to three days. If it lasts longer, or your dog seems unwell at any stage, see a vet.
Is it serious if there is mucus in my dog's poo?
A little mucus often appears with colitis and is common. Combined with blood, frequent straining, or a dog who is unwell, it needs a vet visit.
Can diarrhoea spread to people?
Some causes, such as Giardia and certain bacteria, can. Wash your hands after cleaning up and keep young children away from stools.
Talk with a vet
If your dog has diarrhoea and you are unsure how worried to be, our vets can review the signs with you by video and help you decide whether a clinic visit is needed. Book a consult at dialavet.com. If your dog has bloody diarrhoea with vomiting, is weak, or is a young puppy, go to an emergency vet hospital now. For safe home care, see what you can give a dog with diarrhoea.
References
- Merck Veterinary Manual. Diarrhea in Dogs and Cats; Diseases of the Intestines in Small Animals.
- Jessen LR, et al. European Network for Optimization of Veterinary Antimicrobial Treatment (ENOVAT) guidelines for antimicrobial use in canine acute diarrhoea. The Veterinary Journal, 2024.
- WSAVA Global Nutrition Committee. Global Nutrition Guidelines.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If your pet has bloody diarrhoea, is vomiting, or seems unwell, contact a veterinary hospital promptly.
