Diarrhoea in dogs: causes, home care and warning signs

Overview

Diarrhoea is a symptom of intestinal disturbance or disease elsewhere in the body. It is classified as chronic when it lasts more than three weeks. A duration exceeding three to four weeks is also used as the threshold.

Symptoms can give an initial indication of whether diarrhoea mainly involves the small or large intestine. One dog can show features of both types. In UK dogs receiving primary veterinary care, estimated annual incidence of diagnosed acute diarrhoea was 8.18% in 2019.

In most dogs, acute diarrhoea settles within one week. At UK practices, 1,473 diarrhoea patients, or 80.27%, had only one visit for their first episode.

Causes

Acute diarrhoea can begin after eating something unsuitable outdoors. Switching food too quickly can loosen stools. Some dogs' bowels react to stress, for example when entering boarding kennels. A foreign body lodged in the digestive tract can also cause diarrhoea.

Giardia protozoa can cause intermittent small-bowel diarrhoea. Parvovirus can cause contagious intestinal disease, with bloody diarrhoea in severe cases. Persistent diarrhoea may result from exocrine pancreatic insufficiency, in which food is not digested normally. Hypoadrenocorticism can also cause diarrhoea.

In watery diarrhoea, more fluid than usual may be secreted into the bowel. Undigested nutrients reaching the large intestine can cause diarrhoea as water is retained in the intestinal contents. Chronic intestinal inflammation is one possible cause of recurrent diarrhoea.

Inflammation can impair nutrient absorption if the absorptive surface cells are damaged. Intestinal dysfunction can also impair water reabsorption. Parasites can cause diarrhoea, but a parasite found in faeces can also be incidental.

Risk factors

Puppies aged six weeks to six months whose maternal protection has waned and vaccine protection is not yet established are particularly vulnerable to parvovirus. Weaning or a feeding change may predispose puppies to symptoms from Giardia infection. Access to other dogs' faeces exposes a dog to faecally transmitted infections.

In the UK, acute diarrhoea diagnoses were more common in dogs under three than in those aged four to five. In the same comparison, diagnoses were also more common in dogs over nine than in those aged four to five. Maltese dogs had odds of an acute diarrhoea diagnosis 2.17 times those of crossbreeds. The corresponding odds ratio for Miniature Poodles was 2.17.

Many dogs sharing a space increases Giardia exposure even in adults. In one study from northern Europe, Giardia was found in 19% of symptom-free puppies. In the same study, it was found in 5% of symptom-free adult dogs.

Typical symptoms

Large-bowel diarrhoea often causes a sudden urge to defaecate. With small-bowel diarrhoea, a dog may pass larger volumes without a clear increase in frequency.

• Frequent passage of small amounts with large-bowel diarrhoea.
• Mucus on or within faeces, particularly with large-bowel disease.
• Straining despite passing little faeces.
• Fresh, bright-red blood with large-bowel symptoms.
• Weight loss with persistent small-bowel diarrhoea.
• Vomiting alongside diarrhoea.

Vomiting was also recorded in 44.25% of acute diarrhoea cases examined at UK practices. Appetite was reduced in 27.68% of these dogs. Tiredness was recorded in 24.20%. Bloody diarrhoea was recorded in 29.32% of all cases reviewed.

Foul-smelling flatulence can occur with giardiosis. Parvovirus diarrhoea may be accompanied by fever. Marked weight loss despite a good appetite may suggest pancreatic insufficiency.

Complications and consequences

Profuse diarrhoea can dehydrate a dog when fluid loss exceeds absorption. Concurrent vomiting increases fluid loss. Dehydration can disturb electrolyte balance. Severe dehydration can strain the kidneys.

In acute haemorrhagic diarrhoea syndrome, circulation can fail before dehydration is outwardly apparent. Severe cases can involve sepsis, a serious systemic response to infection. Protein loss associated with chronic intestinal disease can cause abdominal fluid accumulation.

Major fluid loss can cause circulatory failure, or shock. Chronic inflammatory enteropathy can impair nutritional status, particularly with intestinal protein loss. Persistent protein loss can reduce blood albumin.

Diagnosis at the vet

General examination and blood tests

The vet asks when diarrhoea began and whether it is continuous or recurrent. Diet and possible exposure to other dogs are also part of the history. Feeling the abdomen helps assess pain and abnormal intestinal filling, for example. A dog with mild symptoms and good general health does not usually need extensive immediate testing.

Moderate or severe acute diarrhoea warrants a blood count and biochemistry. Blood tests assess dehydration and electrolyte changes to guide fluid therapy, among other factors. CRP can monitor inflammatory severity and change. An adrenal function test may help investigate recurrent acute diarrhoea.

Blood cTLI can investigate pancreatic insufficiency in chronic diarrhoea. With persistent small-bowel diarrhoea, blood cobalamin helps assess intestinal function.

No laboratory tests were performed on the first consultation day in 82.34% of acute diarrhoea cases at the UK practices.

Faecal samples and imaging

Parvovirus testing is appropriate for acute diarrhoea in puppies under six months. For acute bloody diarrhoea, it is recommended in dogs under 12 months. An unvaccinated dog may need testing at any age. If suspicion is strong despite a negative rapid test, PCR can check the result.

A young dog may be tested for Giardia, particularly with persistent or recurrent diarrhoea. Parasite investigation may require faeces from three consecutive days because shedding is intermittent. Faecal bacterial testing is not routine for acute diarrhoea. It may help if several household animals or people develop similar symptoms.

With persistent vomiting or worsening abdominal pain, the vet may use X-rays or ultrasound. Imaging is particularly needed when obstruction or pancreatitis is suspected, for example. An intestinal biopsy can help distinguish inflammatory disease from a tumour.

A positive Giardia result is assessed according to symptoms, as adult infections are often symptom-free.

Treatment

Supportive care and treating an identified cause

Mild diarrhoea can be monitored at home if your dog remains their usual bright self. Small portions of highly digestible food can be offered once any vomiting has eased. Simple home-prepared food may suit short-term use but does not contain every nutrient needed long-term. A dehydrated dog may receive veterinary fluid therapy.

Intravenous fluids are started promptly in severe haemorrhagic diarrhoea. Ongoing fluid loss is considered when planning fluid therapy. Confirmed Giardia infection in a dog with diarrhoea may be treated with medication effective against the protozoan.

When might an antibiotic be needed?

Mild acute diarrhoea is not treated with antibiotics when general health is good and there are no signs of dehydration. A little blood alone does not warrant antibiotics if the vet assesses the disease as mild. Moderate disease generally does not need antibiotics if dehydration-related general symptoms improve with fluids. Exceptions may include blood count changes suggesting severe inflammation, such as low neutrophil numbers.

Antibiotics may be needed in severe disease if general symptoms persist despite adequate fluids. In pooled results, diarrhoea lasted an average of 0.28 days less with antibiotics than in controls. This difference was under 24 hours, below the predefined clinically meaningful threshold. Some antibiotics can alter intestinal microbes for weeks after treatment ends.

Probiotics

Probiotics have not demonstrated a clinically meaningful benefit in treating acute diarrhoea.

Diet for persistent diarrhoea

For persistent intestinal symptoms, a suitable diet may be sought using hydrolysed or novel protein. With persistent large-bowel diarrhoea, the vet may assess whether changing fibre content would help. In an inflammatory enteropathy dietary trial, the agreed food is the sole diet for at least two weeks to assess the response.

Prevention

Change foods gradually, as a rapid switch can trigger diarrhoea. Vaccination is the basis of parvovirus diarrhoea prevention. Weaned puppies need protection from parvovirus exposure until vaccine immunity has developed.

Prompt faeces removal helps reduce faecally transmitted Giardia. Do not take a dog with diarrhoea to a dog park, where infection could spread. If feeding raw food, keep it separate from human food. Wash hands after handling it to prevent bacterial spread.

Giardia's infective stages can survive for months in cool, damp surroundings. With giardiosis, washable dog textiles can be cleaned on a cycle of at least 60°C. A dog infected with parvovirus usually sheds virus for one to two weeks.

Important for dog owners

Keep fresh water available so your dog can replace lost fluid by drinking. Provide more frequent outings if the need to defaecate has increased. Record stool consistency, frequency and any vomiting. Bring a faecal sample if the vet requests one.

Contact a vet if mild diarrhoea does not improve within two to three days, even if your dog remains bright. Do not give human anti-diarrhoeal medication on your own, as it may be harmful. Leave out fatty treats until diarrhoea settles.

Record any recent food change, as a rapid transition may explain onset. Contact the vet earlier if appetite disappears or your dog becomes subdued.

Frequently asked questions

Can I monitor my dog's diarrhoea at home?

Mild acute diarrhoea can initially be monitored at home if the dog is bright and drinking. Repeatedly vomiting back water requires veterinary care. Even mild diarrhoea warrants veterinary assessment if it does not improve within two to three days.

What can black faeces mean?

Black, tarry faeces may contain partly digested blood. Bleeding may come from the upper digestive tract, such as the stomach or small intestine. Fresh red blood is more typical of large-bowel symptoms. Seek urgent veterinary care for black, tarry diarrhoea.

Does a dog with diarrhoea need an antibiotic?

Mild diarrhoea generally does not need antibiotics if general health is good. They may be considered for severe disease whose general symptoms do not improve with adequate fluids. Blood can also occur in a dog that recovers with supportive care.

Can diarrhoea spread to another dog?

Contagiousness depends on the cause: changing food too quickly, for example, is not an infection. Giardia can spread through faeces immediately after infective cysts are shed. Parvovirus usually spreads through an infected dog's faeces.

What does a faecal sample show?

Faecal samples can investigate parasites that cause diarrhoea, among other things. Parvovirus can be sought in diarrhoeic faeces with an immunological or molecular test. A single positive Giardia result does not establish the cause, as many adults have symptom-free infection.