Why does my dog eat grass?

Grass eating is ordinary dog behaviour rather than a symptom. VCA, summarising the published studies, reports that only about 10% of dogs show signs of illness before they eat grass and fewer than 25% vomit afterwards (VCA). If grass were mainly a remedy for a sick stomach, both numbers would be far higher.

The habit also runs in the family. Stool samples show that 11% to 47% of wolves eat grass, which supports the view that dogs inherited it from scavenging ancestors (VCA).

Two pieces of peer-reviewed work add a caution for the minority of dogs who overdo it:

• A JAVMA review of 133 dogs and cats that needed swallowed objects removed from the stomach found chronic gut inflammation in all 41 that were biopsied, and concluded that gut disease should be considered in pica (JAVMA).
• A Miniature Poodle that had eaten plants and vomited daily for 7 years stopped within 3 days of a vet-advised switch to a high-fibre diet (J Vet Med Sci).

Most do not (VCA). When vomiting does follow, there are two patterns.

• The dog felt sick first. Nausea shows as restlessness, lip licking, drooling and repeated swallowing, and a nauseous dog may graze hard (VCA, VCA).
• The grass upset the stomach. Grass can clump together, and too much of it can get stuck and may need surgery to remove (VCA, VCA).

A bright dog that vomits once and then eats and behaves normally can be watched. A dog that seems well but keeps vomiting for more than one to two days needs veterinary care, and so does any dog vomiting with lethargy, diarrhoea, loss of appetite, belly pain or blood (VCA).

The grass itself is rarely the problem. What is on it can be. Herbicides and pesticides sprayed on a lawn can be toxic to dogs (VCA), although Merck notes that vegetation treated at proper rates is not typically hazardous and that most acute poisoning happens when an animal gets at the product itself (Merck).

If you think your dog has eaten something toxic, call your vet or the ASPCA Animal Poison Control Center on (888) 426-4435, which is open 24 hours a day, 365 days a year. A consultation fee may apply (ASPCA).

A change matters more than the habit. VCA says a dog eating grass excessively is likely to be nauseous (VCA). Persistent eating of non-food items is called pica, and its medical causes include gut disease, intestinal parasites, anaemia and an imbalanced diet (VCA).

Things worth noting before you call:

• Whether the grazing is calm or frantic, and whether it is new.
• Any vomiting, diarrhoea, weight loss or change in appetite.
• Whether your dog also eats soil, stones, fabric or other non-food items.
• Any change of food, routine or time left alone.

No source sets a limit, so if the pattern has changed, call your vet to be safe.

Possibly, in some dogs. Grass is a source of roughage that may help digestion (VCA), and the poodle above stopped grazing once its diet changed (J Vet Med Sci). A vet may suggest a higher-fibre food (VCA). Change diet with your vet, so other causes are not missed.

Our sources give no age pattern for grass eating, so we cannot say puppies do it more than adults. Two things matter more for a young dog: worms, so keep up regular deworming (VCA), and asking your vet when it is safe for your puppy to use public grass. Our puppy vaccination schedule explains the timing, and the puppy weight calculator helps you check a growing puppy is on track.

Most dogs do not need to stop. If yours grazes a lot:

• Give more exercise, play, chews and puzzle feeders.
• On walks, when your dog lowers its head to the grass, walk in another direction and reward it with a treat when it follows (VCA).
• Teach "leave it" and "drop it" with rewards, and avoid punishment, which can increase anxiety (VCA).
• Keep your dog off treated lawns, verges and unknown plants.

If licking goes with the grazing, our guide to why dogs lick so much covers lip licking and nausea, and why a dog stops eating explains when a missed meal matters.

Go today if your dog is vomiting and also lethargic, off food, in pain or has diarrhoea, or if poisoning is possible (VCA, ASPCA). Book a visit if grazing has become frantic or new, or your dog eats other non-food items (VCA, VCA). For other changes, the dog behaviour checker hub covers the rest of the cluster.

Every figure and threshold on this page comes from the veterinary sources below, and each one is linked where it is used. Where no source gives a cut-off, we say call your vet rather than invent one.