Serious Question: Why Do Dogs Eat Grass?

Every spring, my dog Avon regularly eats grass -- then barfs it all over the place. What's going on?


In the first few days of spring, when the lawn starts growing in big leafy clumps, my dog Avon has a habit of going out back and eating mass quantities of fresh green dewy grass. Which is no problem, until he barfs it up on my pillow about half an hour later. And during the spring and summer both of my dogs like to stop and grab a few mouthfuls of grass on their morning walk. But some people say that dogs only eats grass because they are feeling unwell, so I wondered whether I should be worried about their grazing habits. Did this taste for grass mean that they were feeling sick?

So I did some research, and found that nobody really knows why dogs eat grass. We know that wolves and other wild canines eat grass, according to a study in 2006, as do large cats and many other wild carnivores. So most researchers assume that dogs have inherited their occasional taste for salad from their wolf ancestors, making it a normal and natural behavior not a side effect of some modern neurosis. But if canines can’t digest grass, this leaves us with the question: is this a behavior that still has a function and so might indicate a health problem or dietary need? Or is it an obsolete evolutionary leftover, like circling around a dozen times before lying down on a comfy dog bed or pulling all the fluffy fur off a plush toy?

In wolves it is suggested that grass might help scour out internal parasites, which should not be a problem for a properly cared for pet dog being maintained on preventative medication and having their stool analyzed at an annual veterinary health check. But the motivation to perform this historically healthy behavior might still remain even when the reason for it is gone.

It is also possible that eating a diverse range of non-toxic foods is a natural way to avoid deficiencies in trace vitamins and minerals. An instinct that might remain helpful, even for dogs now living on ostensibly nutritionally complete commercial diets. After all, it is impossible to know every single tiny element that might benefit the canine body, let alone provide it in every meal.

One case study from Japan in 2007 found that particularly obsessive grass eating by a Poodle was brought under control by providing the dog with a higher-fiber diet. Which suggests that dogs might have a need for roughage that a lot of diets may not meet, not just because of parasites but to maintain healthy function in the gut.

But surveys of dog owners by Sueda, K. L. C. in 2007 have found that how a dog is fed does not relate to whether or not it eats grass. Nor did the surveyed dog owners observe that their dogs seek out grass when they were unwell, or that they vomit after eating it. Which does not tally with the popular theory that dogs eat grass when they have an upset stomach, perhaps with the goal of causing vomiting. In fact, a controlled study by Samantha McKenzie in 2010 found that dogs with a mild case of diarrhea (who might feel the need for more roughage) actually ate less grass than a control group, and vomiting hardly ever occurred in either group.

The only thing that seems to reliably increase grass eating is if the dog is more hungry, which another study revealed. Which makes me wonder if the grass-munching Poodle really needed more fiber specifically, or if it was just the comfort of a full gut cutting down his hunger pangs.

And dogs eat more grass if a particularly tasty species of grass is available, which leads me to speculate that if dogs have any grass-eating impulses at all, the cultivated parks and lawns of the suburbs might provide a tempting over-supply. This abundance, especially in spring, might lead to excessive consumption and perhaps to the barf-y results sometimes exhibited by dogs like Avon.

So if grass eating is at worse benign, and possibly beneficial, it might even be something to encourage in moderation. A planter of sweet oats (aka cat grass) gives my dogs something to snack on when they are alone in the apartment, and they seem to enjoy it. And having ready access seems to reduce their desire to grab huge qualities of grass when they are out on their walks. Since the planter was installed there has been no grass barfing, which I for one appreciate.

My conclusion is this: I certainly need to ensure my dogs stay away from toxic plants or areas that may have been sprayed with chemicals. But the bottom line seems to be that eating grass is normal and not known to be related to any type of illness or nutritional deficiency. So, in the absence of any other worrying symptoms, you can let your dog enjoy his grazing without worrying that it is a cry for help.

But I would be interested in hearing whether anyone else has found that grass eating was a sign that led them to discover their dog had bigger problems or different dietary needs. Because what might be normal for one dog could mean something quite different for another.

About the author: Emily Kane is a New Zealand-born animal behaviorist of the throw-back radical behaviorist type, albeit with a holistic-yuppie-feminist-slacker twist. She spent many years as an animal behavior researcher and is now more of an indoor paper-pushing researcher. Her early dog-related education came from Jess the Afghan Hound and Border Collies Bandit and Tam. It is now being continued by her own dogs and extended dog family and some cats (and her three aquatic snails Gala, Granny and Pippin — they think of themselves as dog-esque).

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