Most dogs eat grass because it is normal dog behaviour, not because they are sick and not because they are trying to make themselves vomit. That is the conclusion of the largest survey ever done on the subject, and of the only controlled feeding experiment on grass eating in dogs. The popular "upset stomach" explanation is the one thing the evidence does not support well.
Here is what researchers have actually measured, which explanations hold up, which don't, and the risks that matter far more than the behaviour itself: what's on the grass. And because a dog that grazes is often a dog whose gut owners want to look after, we cover where a daily digestive routine such as Pure Majesty Pets Liquid Probiotic (60 mL, A$52, free worldwide shipping to Australia with duties and GST prepaid) fits and, just as importantly, what it can't do.
What the research found
In 2008, Karen Sueda, Benjamin Hart and Kelly Cliff of UC Davis published Characterisation of plant eating in dogs in Applied Animal Behaviour Science. They ran three surveys, and they designed them specifically to test the illness-and-vomiting hypothesis.
- 25 veterinary students with dogs: every one reported their dog ate grass. None had ever seen signs of illness beforehand. Only 8% said their dog regularly vomited afterwards.
- 47 owners at a veterinary teaching hospital: 79% had seen their dog eat plants, grass most often. Among the 33 who answered the follow-up questions, signs of illness beforehand were reported for four dogs and occasional vomiting afterwards for six.
- 1,571 usable web surveys from plant-eating dog owners: 68% ate plants daily or weekly. Only 8% frequently showed signs of illness before eating plants, and 22% regularly vomited afterwards.
Hart's own summary of the work is blunt: grass eating is a common behaviour in normal dogs, unrelated to illness, and "vomiting seems to be incidental to, rather than caused by, plant eating."
The survey also found no link between grass eating and diet. Dogs fed table scraps or raw food were no more likely to eat grass than dogs on commercial diets, and dogs on lower-fibre diets were no more likely to eat grass than dogs on higher-fibre ones.
The one controlled experiment, and it is Australian
Surveys rely on owner memory, so the 2007 University of New England study by Bjone, Brown and Price matters. It was published in Recent Advances in Animal Nutrition in Australia, so this one is local research. Twelve healthy, dewormed dogs were offered pots of couch and kikuyu grass three times a day for six days, with every episode filmed and counted.
The result that undercuts the emetic theory: across 709 separate grass-eating events, there were five vomiting events, involving three dogs. If grass were a self-administered emetic, that number should be far higher.
What the experiment did find was a hunger pattern. Dogs spent significantly more time eating grass before their daily kibble meal than after it (2.67 vs 0.53 minutes), and grass eating declined through the day. The longer since the last meal, the more grass. The authors' reading: dogs may simply treat grass as a minor food item.
Myth vs. what the evidence shows
| What you'll read online | What the evidence shows | Source |
|---|---|---|
| "Dogs eat grass to make themselves vomit." | Not supported. 5 vomiting events across 709 grass-eating episodes in the controlled study; only 8% of owners in the large survey saw illness signs beforehand. | Bjone et al. 2007; Sueda et al. 2008 |
| "Grass eating means your dog's stomach is upset." | Weakly supported. It happens in a minority. Dogs that did look ill beforehand were more likely to vomit after, so it isn't zero, just uncommon. | Sueda et al. 2008 |
| "Your dog needs more fibre in its food." | Not supported by the survey data. No association between dietary fibre level and grass eating. | Sueda et al. 2008 |
| "Raw or homemade diets stop grass eating." | No indication of any difference by diet type. | Sueda et al. 2008 |
| "It's an instinct for purging worms." | Interesting hypothesis, not proven in dogs. Based on leaf-swallowing in wild chimpanzees plus the finding that younger dogs eat plants more. Hart presents it explicitly as a hypothesis needing more study. | Hart, dvm360, 2009 |
| "A healthy dog wouldn't do this." | Backwards. All 12 vet-checked healthy dogs in the controlled trial ate grass readily; every one of the 25 vet students' dogs did too. | Bjone et al. 2007; Sueda et al. 2008 |
The explanations, ranked by evidence strength
Best supported: normal inherited foraging behaviour
Grass and plant material turns up in a large share of wolf and cougar scat and stomach samples. Combined with how universal the behaviour is in healthy pet dogs, the leading interpretation is that it is an innate predisposition carried over from wild ancestors, not a symptom.
Moderately supported: hunger and food-seeking
The pre-meal spike in the controlled trial is a real, measured effect in a small sample of 12 dogs. It suggests appetite plays a role, but it comes from one study and should not be over-read.
Plausible but thinly evidenced: boredom, habit, attention
Veterinary behaviour sources commonly list under-stimulation as a contributor, and owners often report the behaviour clusters in dull, unsupervised yard time. There is no controlled study quantifying this in dogs. Treat it as a reasonable working theory, not a finding.
Popular but weakly supported: gastrointestinal discomfort
Real in a minority of dogs, wrong as a general explanation. Hart notes that subclinical gastric upset may occasionally trigger it, and dogs showing illness signs beforehand were more likely to vomit after, but that is a small subset, not the norm.
Speculative: parasite purging
The chimpanzee leaf-swallowing parallel is documented in primates. Extending it to dogs is a hypothesis, and the researchers who proposed it say so.
Not supported: dietary deficiency
The survey data found no diet or fibre relationship. No food or supplement has been shown to stop grass eating, and any product claiming to is making a claim the research does not back. That includes ours: we don't claim Pure Majesty Pets Liquid Probiotic stops grazing, and nothing in this article should be read that way.
The risks that actually matter
The behaviour is usually harmless. What the grass is carrying often isn't.
- Lawn herbicides. A 2013 Purdue study (Knapp et al., Science of the Total Environment) detected herbicides including 2,4-D in the urine of dogs from 19 of 25 households after lawn treatment, and in 14 of 25 before treatment, plus 4 of 8 untreated households, consistent with chemical drift from neighbouring lawns. Herbicide residues were also commonly found on grass from untreated lawns. Hart's own client advice is to keep grass-eating pets off chemically treated lawns. In an Australian suburb, that includes the neighbour's lawn and the nature strip.
- Slug and snail bait. Metaldehyde is the active ingredient in the majority of slug baits worldwide and causes agitation, tremors, seizures and dangerous hyperthermia. There is no antidote. This is an emergency, not a wait-and-see.
- Grass seeds and awns. Barbed seed heads (called foxtails in North America) travel one way only: deeper. They migrate into ears, noses, between toes and occasionally into body cavities, typically causing abscesses. Peak season is summer (December to February in Australia), and seedy dry grass is worth checking after every walk. Bindii (Soliva) is a separate local hazard: it emerges with the May rains and its spiny seeds persist until early December, with the pods able to penetrate paws (Department of Primary Industries and Regional Development, Western Australia).
- Intestinal parasites. Grass fouled by other animals' faeces can carry roundworm and hookworm eggs.
- Lungworm. Angiostrongylus vasorum uses slugs and snails as intermediate hosts. Dogs can pick it up by eating a gastropod hidden in grass, or the slime trail left on it. It is regionally distributed but potentially fatal.
- Paralysis ticks on the east coast. Dogs on the east coast also need paralysis tick (Ixodes holocyclus) vigilance during any time outdoors. The tick is found along the eastern seaboard from North Queensland to Victoria, and the RSPCA Australia advises daily skin checks, watching for hind-leg weakness, a change in bark, retching or drooling (RSPCA Australia Knowledgebase). A University of Queensland study found 73% of ticks on pets were on the head and neck (UQ News, October 2025), so run your fingers around the ears, face and neck after time outdoors.
Where gut support fits (and where it doesn't)
If your dog's grass eating is the normal, clean-lawn kind, there is nothing to fix. But plenty of owners of grazing dogs also deal with loose stools, sensitive tummies or the odd upset after a change in food, and that is a separate question from why dogs eat grass. For that, Pure Majesty Pets Liquid Probiotic is a 3-in-1 daily liquid built to support stool consistency, gut flora and everyday digestion:
- Three live cultures: Saccharomyces boulardii, Bacillus coagulans and Bacillus subtilis. The formula targets 2 billion, 4 billion and 4 billion CFU respectively per 1 mL, 10 billion in total. These are formula targets, not a verified guarantee for every bottle through expiry.
- A prebiotic and yeast cell-wall layer: an inactivated yeast cell-wall preparation (40 mg per 1 mL target) containing MOS and beta-glucans.
- Tributyrin: a source of butyrate (50 mg per 1 mL target) alongside the live cultures.
- A liquid format: shake, measure the serving with the graduated pipette and mix it into food. No powder to scoop and no chew to swallow.
The published research on S. boulardii in dogs supports further interest in digestive use, but it does not establish the efficacy of this complete formulation. A supplement does not treat every cause of diarrhoea; persistent or bloody diarrhoea, vomiting or marked lethargy needs a vet. Follow the serving on your bottle's label. The 60 mL bottle is A$52, and Pure Majesty Pets ships free worldwide: Australian orders arrive with duties and GST prepaid (DDP), nothing to pay on delivery. Shop Pure Majesty Pets Liquid Probiotic.
For more on how probiotics work, read our complete guide to probiotics for dogs and probiotics for dogs with diarrhoea: when they help and when they don't.
A decision framework
Normal: just monitor
Occasional or even daily grazing, no illness before, no vomiting after, normal appetite, normal stools, normal energy. Nothing to fix.
Manage with environment and enrichment
Grazing that looks bored or repetitive, or happens on ground you don't control. Stop lawn treatments or check what your service uses and its re-entry interval, keep dogs off freshly treated grass including neighbours', clear slug bait from the yard, check paws, ears and armpits after walks in dry seedy grass in summer, keep parasite prevention current (including paralysis tick prevention if you live on the east coast), and add a sniff walk or food puzzle before the yard shift.
Book a vet appointment
Grass eating that starts suddenly or escalates sharply; repeated vomiting or retching; reduced appetite; weight loss; ongoing diarrhoea; lethargy; or eating non-food items such as dirt, rocks, fabric or plastic. These are reasons for a veterinary assessment, not a diagnosis, because several unrelated conditions can produce them.
Urgent care now
Suspected slug bait ingestion; tremors, twitching or seizures; blood in vomit or stool; repeated unproductive retching with a bloated or tight abdomen; sudden collapse; hind-leg weakness, a changed bark or drooling in tick country; violent sneezing, head shaking or squinting after being in tall dry grass, which can signal a lodged awn.
Frequently asked questions
Should I stop my dog from eating grass?
Not for its own sake. Healthy dogs eating clean, untreated grass are doing something normal. Redirect based on where the grass is, not the behaviour itself.
Does grass eating mean my dog has an upset stomach?
Usually not. Only 8% of owners of 1,571 plant-eating dogs frequently saw illness signs beforehand. When a dog does look unwell first, that is worth a vet's attention.
Why does my dog eat grass and then throw up?
About 22% of dogs in the large survey regularly vomited afterwards, but the controlled trial recorded only five vomiting events across 709 grass-eating episodes. Frequent vomiting is a reason to see a vet regardless of the grass.
Will more fibre or a diet change stop it?
The survey found no link between fibre intake or diet type and grass eating. No diet or supplement has been shown to stop it.
Is eating grass every day a problem?
68% of dogs in the survey ate plants daily or weekly. Frequency alone is not the warning sign; a sudden change in frequency, or grass eating alongside vomiting, appetite loss or lethargy, is.
Can a probiotic stop my dog eating grass?
There is no research showing that a probiotic, or any supplement, stops grass eating. Pure Majesty Pets Liquid Probiotic is a daily digestive support liquid for stool consistency and gut flora, not a grass-eating fix. If your dog has loose stools, vomiting or other digestive signs, see your vet.
Sources
- Sueda KLC, Hart BL, Cliff KD. Characterisation of plant eating in dogs. Applied Animal Behaviour Science 2008;111:120–132 — ScienceDirect
- Hart BL. Why do dogs and cats eat grass? dvm360, Dec 2009 — dvm360.com
- Bjone SJ, Brown WY, Price IR. Grass eating patterns in the domestic dog, Canis familiaris. Recent Advances in Animal Nutrition in Australia 16 (2007) — une.edu.au
- Knapp DW et al. Detection of herbicides in the urine of pet dogs following home lawn chemical application. Science of the Total Environment 2013;456–457:34–41 — PubMed
- Merck Veterinary Manual — Metaldehyde Poisoning in Animals — merckvetmanual.com
- Merck Veterinary Manual — Lungworm Infection in Dogs — merckvetmanual.com
- Companion Animal Parasite Council — Angiostrongylus vasorum — capcvet.org
- Pet Poison Helpline — Foxtail Grass Foreign Body — petpoisonhelpline.com
- RSPCA Australia Knowledgebase — How can I protect my dog or cat from tick paralysis? — kb.rspca.org.au
- University of Queensland — Paralysis ticks prefer heads and necks of pets — news.uq.edu.au
This article is for general information and does not replace veterinary care. If your dog is unwell, or if the behaviour has changed suddenly, contact your veterinarian. In a suspected poisoning, contact your vet or an animal poison control service immediately.