Quick summary
Mild diarrhoea in an otherwise happy, eating, drinking adult dog often resolves in 24-48 hours with home care. What changes the picture is: how old, how long, how much blood, and how they look in themselves.
Red flags — go to a vet
Emergency (go now):
- Black, tarry stool (digested blood — serious GI bleeding)
- Large amounts of fresh red blood
- Puppy under 4 months with profuse diarrhoea (risk: parvovirus, rapidly fatal)
- Severe lethargy, collapse, pale gums
- Diarrhoea + persistent vomiting in any dog
Soon (24-48 hours):
- Diarrhoea persisting more than 48 hours
- Small streaks of fresh blood
- Dog is off food, drinking less, less bright than normal
- Any senior dog or dog with known conditions
- Mucous or jelly-like stool
Home care (for mild cases, adult dogs only)
If your adult dog has mild diarrhoea but is bright, eating, drinking, and otherwise well:
- Withhold food for 12 hours. Water is important — offer small amounts often.
- Introduce a bland diet: boiled chicken breast (no skin, no seasoning) with white rice, in small meals, every 4-6 hours.
- Over the next 2-3 days, transition back to normal food by mixing.
- Monitor: passing normal stool, stopping vomiting, staying bright and hydrated.
What NOT to do:
- Do not give human anti-diarrhoeal medications (loperamide / Imodium can be harmful in some breeds — MDR1-mutation collies and related breeds especially)
- Do not give probiotics as a substitute for a vet visit if signs are severe
- Do not give home remedies containing garlic, onion, or xylitol (toxic)
Common causes
- Dietary indiscretion — most common
- Stress (change of environment, travel, kennelling)
- Dietary change (new food introduced too quickly)
- Intestinal parasites (worms, giardia)
- Bacterial or viral infection
- Pancreatitis
- Inflammatory bowel disease (chronic cases)
- Food intolerance or allergy
Dehydration check
Pinch the skin on the back of the neck and release. It should snap back immediately. If it stays tented for even a second or two, your dog is dehydrated and needs fluids from a vet.
Also check gums — should be wet and slick. Dry or tacky = dehydrated.
When puppies are different
Puppies dehydrate fast. Any diarrhoea in a puppy under 6 months lasting more than 12 hours, or combined with vomiting or lethargy, warrants a vet call. Parvovirus is the specific concern in unvaccinated pups.