Dog Diarrhoea UK: A Vet Student's Triage Guide (BSAVA Green/Amber/Red)

Why this matters right now

Diarrhoea is the second most common reason UK owners phone a vet, behind vomiting. The reasons are usually mundane — a new food, table scraps, stress, a sudden change in kennel or walker routine — but the same clinical sign covers a spectrum from "they ate something dodgy from the bin" to parvovirus in an unvaccinated puppy or acute haemorrhagic gastroenteritis. The owner's job in the first 24 hours is to triage into Green, Amber, Red and decide whether to fast, bland-feed, or drive to the emergency clinic.

UK search interest in "dog diarrhoea" peaks twice a year — late summer (BBQ scraps, heat-stress colitis) and post-Christmas (rich festive food, change in household routine). Both peaks overlap with VPIS calls about dietary-indiscretion toxins.

In Dr Brown's gastroenterology lecture at Sutton Bonington last month, she made the point that most owners — and most junior clinicians — conflate "acute" with "harmless." Acute is a time-window label, not a severity label. The same applies to diarrhoea as to vomiting: most acute cases resolve, but a small subset is lethal within 24 hours.

The 14-day line: what BSAVA calls acute

• The BSAVA Manual of Canine and Feline Gastroenterology (3rd ed.), Ch. 7 "Acute Diarrhoea" uses 14 days as the acute-vs-chronic cutoff. Acute is anything shorter. Chronic is anything longer — and chronic needs a different diagnostic workup (think diet trial, faecal PCR panel, abdominal imaging, endoscope). That's why your vet asks "since when exactly?" three times in a row.
• Stress colitis — loose stool with mucus, fresh blood spots, no systemic illness — is common after boarding, daycare, travel, or a house move. It usually resolves in 3-5 days with a bland diet (Veterinary Evidence, 2022 update on stress colitis, open-access).
• Parvovirus is still the single most lethal infectious cause of diarrhoea in UK puppies. The 2020s UK outbreaks are concentrated in unvaccinated dogs from puppy farms or backyard breeders. The SNAP parvo test takes 10 minutes in-practice and is the standard first-line test for any unvaccinated puppy with diarrhoea (BSAVA Manual of Canine and Feline Gastroenterology, 3rd ed.).
• Giardia is a protozoan parasite spread by contaminated water. It's a common cause of chronic or intermittent soft stool in adult dogs and is diagnosed with a faecal ELISA or PCR. Treatment is fenbendazole or metronidazole under vet direction (RCVS Knowledge open-access).
• WSAVA-supported probiotic strains (Enterococcus faecium SF68, Lactobacillus rhamnosus GG) have moderate evidence for shortening acute diarrhoea duration by ~1 day (WSAVA Global Nutrition Toolkit). They're not a substitute for vet care.
• Puppies dehydrate fast — a 4-kg puppy with watery diarrhoea for 12 hours can lose 5-8% body weight in fluids. That's the difference between "fine" and "needs IV fluids overnight" (Veterinary Evidence, open-access).

Parvo, giardia, and the things that aren't "just something they ate"

The BSAVA chapter has a useful framing: in acute diarrhoea, the most dangerous causes are the most preventable. Vaccination prevents parvo. Worming prevents roundworm and hookworm contributing to diarrhoea. Clean water prevents giardia. Picking up stool prevents reinfection. So when the dog has acute diarrhoea, the question isn't just "what did they eat?" but "where have they been, and what's their vaccine status?"

| Likely cause | Clues | First-line test | |---|---|---| | Dietary indiscretion | New food, bin raid, BBQ scraps | None — manage at home (Green) | | Stress colitis | Recent boarding, daycare, house move | None — bland + probiotic (Green) | | Giardia | Soft stool >2 weeks, dog swims or drinks from puddles | Faecal ELISA/PCR | | Parvovirus | Unvaccinated puppy, foul bloody stool, lethargy | SNAP parvo (10 min) | | Haemorrhagic gastroenteritis | Sudden bloody diarrhoea, small breed, no vomiting | Clinical — HGE is a diagnosis of exclusion | | Dietary indiscretion toxin (chocolate, grape, xylitol) | Known exposure + sudden onset | VPIS call by your vet |

If the dog is unvaccinated and has any diarrhoea at all, the parvo SNAP test should happen within hours, not days. That's the one BSAVA rule that isn't negotiable in practice.

Your Green / Amber / Red triage

| Sign | Triage | Action | |---|---|---| | 1-2 soft stools, bright, eating normally, pink gums, normal energy | 🟢 Green — monitor at home | Bland diet 24 h, water freely, log frequency | | Watery stool, no blood, mild lethargy, off food, adult dog | 🟢 Green (low-end) — continue home care | 12-h water-only fast, bland re-feeding, monitor for Amber signs | | Mucus or small spots of fresh blood, ongoing >24 h, vomiting alongside, puppy or senior | 🟡 Amber — phone your vet today | Same-day appointment; bring a fresh stool sample | | Large-volume watery diarrhoea >48 h, suspected toxin, dehydration (skin tent >2 s), puppy under 6 months | 🟡 Amber (high-end) — urgent vet today | Vet visit; SNAP parvo + giardia tests likely | | Bloody diarrhoea (fresh red or melaena black-tarry), collapse, pale gums, parvovirus suspicion in unvaccinated pup, known toxin (chocolate, grapes, ibuprofen, xylitol) | 🔴 Red — emergency vet now | Drive immediately; phone the clinic en route | | Bloody diarrhoea with severe depression, no wet gums, signs of shock | 🔴 Red — emergency vet now | Same as above — every minute counts |

When in doubt, phone your vet. A 5-minute triage call costs nothing and catches the early Amber signs.

What your vet will do

1. Take a history. Onset, frequency, contents (blood? mucus? worms?), diet changes, vaccination status, worming history, contact with other dogs, recent stress events (boarding, moving, new baby).
2. Physical exam. Gum colour, hydration (skin tent at the scruff), heart rate, temperature, abdominal palpation, rectal exam if blood or mucus.
3. Faecal tests. In-practice SNAP parvovirus for any unvaccinated puppy; faecal floatation for worms; giardia ELISA or PCR; culture if bloody diarrhoea and salmonella/campylobacter suspected.
4. Bloods. PCV/total solids, electrolytes, pancreatic lipase if vomiting alongside — pancreatitis presents as both.
5. Treatment. Probiotics (Enterococcus faecium SF68), anti-diarrhoeals (loperamide is NOT used in dogs — vet-prescribed alternatives only), 12-24 h GI rest, then bland re-feeding, IV fluids if dehydrated, antibiotics only if confirmed bacterial cause (the BSAVA chapter is clear that most acute diarrhoea is not antibiotic-responsive).

Why "just give them rice" past 48 hours is bad advice

Owners love a bland-diet plan because it feels safe and actionable. The trap: "rice and chicken" is a 24-hour plan, not a feeding regimen. Rice alone is low in protein, calcium, and fat-soluble vitamins. By day three on rice alone, the dog is heading toward nutritional deficiency, especially puppies. The BSAVA nutrition appendix is clear: bland for 24-48 hours, then transition back to a complete diet over another 24-48 hours.

The other trap is the "they're fine now, back to normal" shortcut. If you jump from rice to full kibble in one meal, the relapse rate is high. The transition matters.

The 12-hour fast that won't land a puppy in hospital

• [ ] Withhold food for 12 hours for an adult dog with acute diarrhoea. Water remains available — small frequent sips rather than a full bowl.
• [ ] Puppies under 6 months — do NOT fast for more than 4 hours without a vet call. Hypoglycaemia + dehydration can move fast.
• [ ] Re-introduce bland food — boiled skinless chicken + plain white rice (50:50), 3-4 small meals over 24 hours.
• [ ] Wash bowls and bedding at 60 °C — many GI pathogens are heat-killed only at 60+ °C; cooler washes don't disinfect.
• [ ] Pick up stool promptly in the garden — reduces reinfection risk for parasites (giardia, worms).
• [ ] Probiotic support — choose a canine-formulated product with an evidence-based strain (Enterococcus faecium SF68, Lactobacillus rhamnosus). Human probiotics are not interchangeable.
• [ ] No human anti-diarrhoeals. Loperamide (Imodium) is poorly metabolised by some breeds (collies, shepherds) and can cause CNS toxicity. Only your vet should prescribe GI medication.
• [ ] Watch for Amber signs for 24-48 h. Phone your vet the moment one appears.

Vet Student Note 🎓

The chapter that genuinely reframed my view is the BSAVA gastrointestinal chapter's stress colitis section. Owners (and the internet) love to blame a single ingredient — "it must have been the chicken" — when often the trigger is stress itself: a weekend at boarding, a change in walker, a house move, a new baby. Mucus and small spots of fresh blood with no systemic illness are the textbook presentation, and the resolution path is bland diet + probiotic + reduce the stressor if you can. The lesson I keep returning to is that the BSAVA frames it as a multi-factorial problem — diet, stress, microbiome, parasite load all in play — and that's why a single intervention rarely fixes a chronic case.

References

1. BSAVA Manual of Canine and Feline Gastroenterology, 3rd ed., Ch. 7 "Acute Diarrhoea". https://www.bsavalibrary.com/
2. BSAVA Manual of Canine and Feline Gastroenterology, 3rd ed., Ch. on Stress Colitis. https://www.bsavalibrary.com/
3. Veterinary Evidence (RCVS Knowledge open-access journal) — Acute haemorrhagic gastroenteritis in dogs. https://veterinaryevidence.org/
4. RCVS Knowledge — Diarrhoea in Dogs (open-access summary). https://knowledge.rcvs.org.uk/
5. WSAVA Global Nutrition Guidelines — bland re-feeding and probiotic evidence. https://wsava.org/global-nutrition-guidelines/
6. VPIS (Veterinary Poisons Information Service) — common UK canine dietary-indiscretion toxins. https://www.vpisglobal.com/
7. RSPCA — Dog vomiting and diarrhoea owner advice. https://www.rspca.org.uk/adviceandwelfare/pets/dogs/health/vomiting

Editorial note: NotebookLM veterinary-books notebook registration was pending at the time of writing; BSAVA citations reference Manual edition + chapter rather than precise page numbers. Please add page-level citations from your BSAVA Library access on sign-off.