The short answer
Most likely because it’s a normal behaviour, not because they’re sick. A survey of 1,500 dog owners found that nearly 70% reported their dogs eating grass daily or at least weekly. Less than 25% of dogs vomit afterward, and fewer than 10% show signs of illness before eating grass.
The “self-medicating” myth
The common belief is that dogs eat grass to make themselves vomit when they feel sick. The research doesn’t support this. A study from UC Davis found that only about 22% of dogs vomited after eating grass, and only 9% showed signs of illness beforehand. Most dogs eat grass, feel fine before, feel fine after, and move on with their day.
That doesn’t mean it never happens. Some dogs do eat grass and vomit. But for most dogs, grass eating is just something dogs do.
Actual reasons dogs eat grass
Fibre supplementation. Dogs need roughage in their diet, and grass is fibre. Some researchers believe dogs eat grass to supplement dietary fibre, which helps with digestion and regular bowel movements. If your dog eats grass frequently and their food is low in fibre, that might be worth discussing with your vet.
Instinct. Wild canids (wolves, coyotes) eat grass regularly. It may serve as a natural de-worming mechanism by wrapping around intestinal parasites and helping expel them. Domestic dogs may have retained the behaviour even though most aren’t carrying worms (assuming they’re on heartworm and parasite prevention).
Taste and texture. Some dogs seem to genuinely enjoy it, especially fresh spring grass. There may not be a deeper reason than that.
Boredom. Dogs that are understimulated may graze as something to do. If the grass eating only happens when your dog is alone in the yard with nothing else going on, boredom is a reasonable guess.
When to worry
Occasional grass eating is not a concern. But talk to your vet if your dog is eating grass obsessively (constantly seeking it out, eating large amounts), vomiting repeatedly after eating grass, showing other signs like weight loss, diarrhea, or lethargy, or if they might be eating grass treated with pesticides or herbicides.
That last point matters in Oakville. Ontario’s cosmetic pesticide ban (in effect since 2009) prohibits over 250 pesticides for residential lawn use, so treated lawns are less common here than in many US jurisdictions. But some products remain legal for specific uses, and commercial properties and parks may still be treated. When in doubt, keep your dog off grass you didn’t maintain yourself. Grass treated with chemicals is also a concern for dogs with grass allergies, though for different reasons.
Key takeaways
- Grass eating is normal dog behaviour. About 70% of dogs do it regularly.
- Less than 25% of dogs vomit after eating grass. Fewer than 10% are sick beforehand.
- Likely reasons: fibre supplementation, instinct, taste, or boredom.
- Occasional grass eating doesn’t need treatment. Obsessive eating or repeated vomiting does.
- Avoid letting your dog eat chemically treated grass.
References
- VCA Animal Hospitals. “Why Dogs Eat Grass.” vcahospitals.com
- PetMD. “Why Do Dogs Eat Grass?” petmd.com
- AKC. “Why Does My Dog Eat Grass?” akc.org
- Sueda, K.L. et al. “Characterisation of Plant Eating in Dogs.” Applied Animal Behaviour Science, 2008.