Dog Diarrhoea: What Every Owner Needs to Know
Diarrhoea is among the most common reasons dog owners seek veterinary advice. Most dogs will experience it at some point in their lives, and the causes range from the completely trivial — eating something they should not have — to the genuinely life-threatening. Knowing the difference, and recognising the warning signs that demand urgent attention, is something every dog owner should understand.
Acute Versus Chronic Diarrhoea
Acute diarrhoea comes on suddenly and typically lasts a few days at most. In many cases, it has an identifiable cause such as dietary indiscretion or a sudden change in food, and resolves with basic management. Chronic diarrhoea is persistent or recurrent — lasting more than two to three weeks, or coming and going over a period of months. Chronic diarrhoea always warrants veterinary investigation, as it suggests an ongoing underlying problem such as inflammatory bowel disease, a food intolerance, parasites, or organ disease.
Small Intestine Versus Large Intestine Diarrhoea
Identifying where in the gut the problem originates can help narrow down the cause. Small intestinal diarrhoea tends to produce large volumes of loose, watery stool. The dog may not need to strain to go and often goes less frequently. Weight loss can occur over time if nutrients are not being absorbed properly.
Large intestinal diarrhoea, originating from the colon, tends to produce smaller, more frequent amounts of softer stool. Dogs often strain and appear to need to go urgently. You may notice mucus coating the stool, or spots of fresh, bright red blood on the surface. While blood in the stool is always worth reporting to a vet, small amounts of fresh red blood on the surface of an otherwise soft stool in an otherwise well adult dog is less immediately alarming than the dark, tarry stools that indicate bleeding higher in the digestive tract.
Common Causes of Diarrhoea in Dogs
Dietary Indiscretion
This is by far the most common cause of acute diarrhoea in dogs. Dogs eat things that do not agree with them — raided bins, scavenged scraps, dead animals, garden plants, and the occasional sock. The gut reacts accordingly. A single episode in an otherwise bright and well dog after a known dietary escapade is usually manageable at home, as long as no red flags are present.
Sudden Diet Change
Changing a dog's food too quickly disrupts the balance of bacteria in the gut and frequently causes loose stools. Always transition to a new food gradually over seven to ten days, mixing the old and new food in increasing proportions.
Stress
Dogs can develop diarrhoea in response to stressful events — moving house, fireworks, a stay in kennels, or a new addition to the family. This type of diarrhoea is usually short-lived and resolves once the stressor passes.
Parasites
Intestinal worms, Giardia, and Cryptosporidium are all parasites capable of causing diarrhoea in dogs. Giardia in particular is commonly overlooked and can cause persistent, soft, greasy-looking stools. Routine worming helps protect against common worm burdens, but Giardia requires specific treatment and is detected through faecal testing. If your dog has ongoing loose stools that are not responding to basic management, a faecal analysis is a sensible early step.
Bacterial Infections
Bacteria such as Campylobacter and Salmonella can cause acute diarrhoea in dogs, sometimes with blood and mucus in the stool. These infections can occasionally be passed to humans, so hygiene is particularly important when dealing with a dog that has bacterial gastroenteritis — wash your hands thoroughly after handling the dog or cleaning up faeces.
Viral Infections: Parvovirus
Canine parvovirus is a serious, potentially fatal viral disease that attacks the lining of the intestine and suppresses the immune system. It causes severe, profuse, often bloody diarrhoea alongside vomiting, lethargy, and loss of appetite. Puppies and unvaccinated dogs of any age are most at risk. Parvovirus spreads very easily through the environment and contaminated faeces. Any puppy or unvaccinated dog showing these signs requires emergency veterinary care immediately. Vaccination is highly effective at preventing parvovirus and is a core part of the standard vaccination programme.
Food Intolerance
Some dogs have difficulty digesting specific ingredients, leading to chronic or recurrent loose stools. This often runs alongside other signs of intolerance such as itchy skin or vomiting. An exclusion diet trial under veterinary guidance can help identify the problem ingredient.
Antibiotics and Medication
Antibiotics disrupt the normal balance of bacteria in the gut, frequently causing loose stools as a side effect. This usually resolves once the course of antibiotics is complete. Probiotics can help support gut flora during and after antibiotic treatment — ask your vet about appropriate products.
Red Flags: When Diarrhoea Is an Emergency
Contact your vet urgently or go to an emergency clinic if your dog has diarrhoea and any of the following apply:
- There is blood in the stools — whether bright red or dark and tarry (the latter is especially serious)
- Diarrhoea has lasted more than 24 to 48 hours without improvement
- Your dog is also vomiting, is lethargic, or appears collapsed or weak
- Your dog is a puppy, especially if unvaccinated
- You suspect ingestion of a toxin or a dangerous substance
- Your dog is very young, very old, or has existing health conditions
- Diarrhoea is profuse and watery, occurring very frequently
Checking for Dehydration
Diarrhoea causes fluid loss and can lead to dehydration, which is particularly dangerous in puppies and older dogs. A simple way to check hydration at home is the skin turgor test: gently pinch the skin on the scruff of the neck, lift it slightly, and release. In a well-hydrated dog, the skin springs back immediately. If it stays tented or returns to normal slowly, the dog may be dehydrated and needs veterinary attention. In addition, check whether the gums appear moist and pink — dry, tacky gums are another sign of dehydration.
Home Care for Mild Cases
For an otherwise healthy adult dog with mild diarrhoea and no red flags, home management is often appropriate for the first 24 hours. A short fast of four to six hours can allow the gut to settle — ensure fresh water is always available. After the rest period, introduce a bland diet in small, frequent amounts. Plain boiled chicken breast with boiled white rice, or plain boiled white fish, is easy to digest and gentle on the gut. Continue this diet for two to three days before gradually reintroducing normal food.
Probiotics designed for dogs — such as Protexin or FortiFlora — can help restore a healthy gut flora and may speed recovery. These are available from vets and pet shops.
Never give your dog human anti-diarrhoea medications such as loperamide (Imodium) without specific veterinary guidance. While some vets do prescribe it in certain situations, it is not appropriate in all cases and can be harmful if the diarrhoea has an infectious cause. If your dog's stools have not returned to normal within 48 hours of home management, or if any red flags develop at any point, contact your vet.