Why Do Dogs & Cats Eat Grass?

Updated November 29, 2020

“If a dog eats grass it means they are going to die”. Amazingly I still hear this from time to time. Usually it’s not quite that dramatic.

Dogs and cats eat grass for a variety of reasons, some good, some bad.

Why Do Dogs Eat Grass?

There are two simple reasons why dogs eat grass:

• Normal behaviour
• A sign of illness

A dog who eats grass normally will nibble at grass tips most days but never eat a lot. They might do it for a minute or two and then lose interest. They are bright, happy and hungry.

A dog who eats grass due to illness will usually eat a lot more than usual, sometimes until they fill their stomach. If the illness persists they may return to it again and again. Grass eating due to sickness happens in an on-and-off pattern and is usually associated with being quiet or losing interest in food.

Normal instinctive grass eating probably acts to supply minor essential nutrients that may be missing from a wild dog’s diet. It shouldn’t be necessary for a dog on a balanced and complete diet, but if it doesn’t do any harm, why worry.

Do dogs eat grass to make themselves vomit?

An American researcher once told me of her study where they fed coyotes sheep meat laced with substances designed to cause nausea (that queasy feeling). The idea was to reduce sheep killing (which didn’t work) but they did notice one interesting thing: the coyotes ate a lot of grass afterwards.

Since then, Australian researchers have induced diarrhoea in dogs and found that dogs ate less grass, not more. They also found that dogs have taste preferences, preferring kikuyu to couch grass (McKenzie et al, 2010).

Abnormal grass eating is usually a sign that your dog is feeling nauseous. They aren’t trying to make themselves sick, they feel sick. The causes include:

• Gastroenteritis (e.g. eating something they shouldn’t)
• Food intolerance
• An intestinal blockage
• Pancreatitis
• Liver failure or kidney disease
• Even tonsillitis
• Read more at What causes dogs to vomit?

Most puppies who start eating a lot of grass have swallowed something bad, and should be seen by a vet straight away. Sometimes they will eat enough grass that it causes an obstruction all by itself. For this reason, stop them eating more than a few nibbles.

Adult dogs should also see the vet but it may not be an emergency if they are bright and playful. Important chronic diseases like pancreatitis require blood testing, and food intolerances are only diagnosed once these important ‘sleeper’ diseases are ruled out.

Why Do Cats Eat Grass?

Cats are strict carnivores and probably eat grass to supplement their diet with essential vitamins.

Unlike dogs, cats don’t usually eat grass when they feel sick. Most cats who eat grass are simply exhibiting normal instinctive behaviour.

Cats like to eat grass and it should be offered to all indoor cats.

When is grass eating a problem?

The danger is when cats don’t get access to grass and try to eat alternatives. If a cat kept inside wants to nibble grass but can’t, they will often try other indoor plants instead.

Many cut flowers and ornamental plants are toxic to cats. Lilies in particular are known to cause kidney damage and kidney failure. We have seen a few confirmed cases of lily poisoning but fear that in most cases of kidney failure, the cause goes unrecognised.

So even if it seems crazy, as long as they do it in moderation, let those doggies and kitties unleash the tiny cow within.

McKenzie, S. J., Brown, W. Y., & Price, I. R. (2010). Reduction in grass eating behaviours in the domestic dog, Canis familiaris, in response to a mild gastrointestinal disturbance. Applied Animal Behaviour Science, 123(1), 51-55.

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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.