Why Is My Dog’s Poo Green? Causes, Health Risks & When to See a Vet
Worried because your dog’s poo is green? Learn the causes of green stools in dogs—from diet and grass eating to parasites and health conditions—and when to seek veterinary help.
Introduction
Dog owners are well-acquainted with the daily ritual of checking their pet’s stools. It might not be glamorous, but your dog’s poo is one of the clearest windows into their health. Colour, consistency, frequency, and smell can all provide clues about what’s going on inside your dog’s body.
So, what if you suddenly notice green poo in your dog? While it may be alarming at first, not all causes are dangerous. In some cases, diet or a simple snack of grass might be to blame. But in others, green stools can signal infection, parasites, or liver and gallbladder issues that need veterinary attention.
This comprehensive guide explores why your dog’s poo might turn green, when to worry, and what steps to take.
Normal Dog Poo: What Should It Look Like?
Before diving into green stools, it helps to understand what healthy dog poo looks like.
Colour: Medium to dark brown (caused by bile pigments such as stercobilin).
Consistency: Firm, log-shaped, but easy to pick up.
Frequency: 1–3 times per day for most adult dogs, though puppies and seniors may differ.
Contents: No visible mucus, blood, or large chunks of undigested food.
Any major change in colour—including green—suggests something is altering digestion, bile metabolism, or stool composition.
Top Causes of Green Dog Poo
1. Grass Eating
Dogs are notorious for eating grass. While the exact reason isn’t fully understood, theories include:
Instinctual fibre intake
Relief from nausea or upset stomach
Simply because they enjoy the taste
If your dog eats large amounts of grass, undigested chlorophyll (the green pigment in plants) may pass through the digestive tract, giving stools a green colour.
When to worry: If your dog is vomiting, eating grass obsessively, or producing diarrhoea alongside green poo, further investigation is needed.
2. Diet & Food Colourings
Certain foods, treats, or supplements can temporarily tint stools green. Examples include:
Dark leafy greens (spinach, kale)
Spirulina, chlorella, kelp, or green superfood powders
Food dyes in commercial treats
Tip: If you recently added new treats or toppers, remove them and monitor stool colour for 48 hours.
3. Rapid Gut Transit
If food moves too quickly through your dog’s intestines, bile doesn’t have time to fully break down into its normal brown pigments. Instead, bile salts may remain green, resulting in green poo.
Common triggers:
Sudden dietary change
Stress or anxiety
Infections causing diarrhoea
High-fat or greasy foods
4. Gastrointestinal Infections
Bacterial, viral, or protozoal infections can inflame the gut, disrupting bile metabolism. Giardia in particular is notorious for causing green, foul-smelling diarrhoea in dogs.
Signs of infection include:
Watery or slimy stools
Blood or mucus
Vomiting
Lethargy
Loss of appetite
Veterinary testing (faecal exam, PCR, ELISA) is essential to identify and treat parasites or pathogens.
5. Liver & Gallbladder Disease
The liver and gallbladder play a vital role in producing and storing bile, which helps digest fats and colours faeces brown. If bile is not processed correctly, stools may appear yellow-green or clay-coloured.
Conditions to consider include:
Hepatitis
Cholangitis
Gallstones
Bile duct obstruction
Accompanying signs: jaundice (yellow gums/eyes), weight loss, poor appetite, vomiting, and abdominal discomfort.
6. Pancreatic or Bile Disorders
Disorders affecting the pancreas (such as exocrine pancreatic insufficiency) or bile flow can interfere with digestion, leading to greasy, pale, or greenish stools.
Dogs with malabsorption issues may also have diarrhoea, bloating, and unexplained weight loss.
7. Toxin or Foreign Body Ingestion
Some toxins and rodenticides contain green or blue dyes. If your dog ingests these, you may notice:
Vividly green stools
Vomiting
Weakness or collapse
Seizures
This is a medical emergency—seek veterinary care immediately.
When Is Green Poo an Emergency?
Call your vet urgently if green poo is accompanied by:
Vomiting, especially if persistent
Diarrhoea lasting more than 48 hours
Lethargy or collapse
Blood or black, tarry stools
Abdominal swelling or pain
Yellowing of eyes or gums (jaundice)
Diagnostic Approach at the Vet
A veterinarian may use the following to investigate green stools:
History & diet review – recent food, treats, toxins, supplements.
Physical exam – palpating the abdomen, checking hydration.
Faecal tests – flotation, ELISA, PCR for parasites like Giardia.
Bloodwork – liver enzymes, bile acids, pancreatic values.
Imaging – ultrasound or X-ray to assess gallbladder, liver, or gut.
Treatment Options
Treatment depends on the underlying cause:
Grass or food-related: No treatment, just monitoring and dietary adjustment.
Infections: Antibiotics, antiparasitic medication, fluid therapy.
Liver/gallbladder disease: Special diets, bile acid modifiers, surgery if obstruction present.
Toxins: Immediate decontamination, activated charcoal, intensive care.
Dietary intolerance: Switching to a balanced, easily digestible diet.
Nutritional Considerations
As a canine nutritionist, I recommend:
Gradual food transitions: Always transition diets over 7–10 days.
Digestible proteins: Lean meats like chicken, turkey, or white fish.
Low-fat diets: Helpful in cases of bile or pancreatic issues.
Fibre sources: Pumpkin, psyllium husk, or beet pulp can help regulate stool.
Probiotics: Can support gut health during recovery.
Prevention Tips
Avoid sudden food changes.
Keep dogs away from toxins, rubbish, and unknown plants.
Choose complete, balanced diets that meet FEDIAF/NRC standards.
Use parasite preventatives as recommended by your vet.
Monitor stool colour and consistency regularly.
Final Thoughts
Green dog poo can be as harmless as a grass snack—or as serious as liver disease. Context is everything. If your dog is otherwise bright, active, and eating well, the cause is often dietary and short-lived. But if symptoms persist or your dog appears unwell, veterinary attention is vital.
Keeping a stool diary and noting diet, behaviour, and any colour changes can help your vet identify patterns quickly.
References
Hall EJ, German AJ. Diseases of the Small Intestine in Dogs. BSAVA Manual of Canine and Feline Gastroenterology, 2014.
Marks SL, Kather EJ. “Bacterial-associated diarrhoea in the dog.” Journal of Small Animal Practice. 2003;44(1):4-13. DOI
Robertson ID, Thompson RC. “Enteric parasitic zoonoses of domesticated dogs and cats.” Microbes and Infection. 2002;4(8):867-873. DOI
Willard MD, Twedt DC. “Gastrointestinal, pancreatic, and hepatic disorders.” Textbook of Veterinary Internal Medicine, 2017.
ESCCAP UK & Ireland. Worm Control in Dogs and Cats. 2020. Link
Merck Veterinary Manual. “Diarrhoea in Small Animals.” Link
Having issues with your dog’s stools? Book in a consult now OR Start with a free diet assessment at www.thecaninedietitian.co.uk.
