Every so often someone asks me why do dogs eat grass. Everyone says they do it to vomit, but this response doesn’t sit well with me. Does your dog always vomits after eating grass? Mine certainly doesn’t.

In this post I’ll explain what we really known about why dogs eat plants and weeds and what scientific evidence exists to show they don’t always eat grass to vomit. Finally, I’ll explain whether it’s a good idea to allow a dog to eat grass or not.

Dogs eat grass then vomit?

This has probably also happened to you: about half an hour after eating grass, your dogs vomit a mass of undigested weeds in which we can easily identify every blade of grass they ate!

It’s a little gross, but it’s usually down to us to clean up after their little ‘green’ party. Do dogs always throw up after eating grass? No, not always. They often eat it with no consequences, although why they do so is a mystery whose answer has yet to be fully revealed …

The false myth that a dog eats grass to induce vomiting

How many times have I been asked why do dogs eat grass? It’s the typical question both owners and those not into dogs ask about. It can be striking to see a carnivore chewing the cud with ease… and then watching it throw up afterwards, as often happens.

However, for a while now, I’ve refused to accept the common response: “dogs eat grass to vomit”. And I’m not just playing Devil’s advocate here: that answer doesn’t make sense even in the case of my own dog. He is the first to eat grass when we go for a walk and he’s only ever vomited a few times. In addition, he’s rarely shown symptoms of having an upset stomach before eating grass. When it comes down to it, something doesn’t add up …

If a dog eats grass to purge, how come it doesn’t always vomit afterwards? Why do they usually show no symptoms of being sick before eating? Simply put: the ‘purging’ explanation is not always a valid explanation.

Other explanations are not valid either

Another common explanation used in response to the question of why dogs eat grass is that they’ve inherited this innate behavior from their wild ancestors, the wolves.

Dogs evolved from wolves, which hunt and eat animals that primarily eat grass, such as mice, rabbits, deer, etc. When wolves eat their prey they are also ingesting the plant material within the prey’s stomach and intestines. It is thought that this plant material may be of nutritional value to canines, and it might even be an essential component in contributing fiber to their diet.

Some vets suggest dogs eat grass to satisfy this requirement of nutrients and fiber, just as their ancestors the wolves do. However, as of today there are no scientific studies to confirm this theory.

Science, dogs and grass

There is a surprising lack of scientific studies for a question as common as why dogs eat grass. After much searching, I finally discovered an article that gave me some interesting insight. It was this article, published in the journal Psychology Today, and written by canine psychologist and ethologist Stanley Coren, who I’ve been a fan of for some time.

The article quotes one of only two scientific studies to be carried out so far to discover why dogs do eat grass, a study from 2008 published in the Journal of Applied Animal Behaviour Science, which I will discuss below.

I found the other article after searching high and low on the Internet. It’s from 2007: ” Grass eating patterns in the domestic dog, Canis familiaris “. Their research suggests that dogs eat grass more often when they’re hungry than when they’re full-up.

A scientific study refutes that dogs eat grass to purge

This 2008 study, conducted by scientists at the University of California, sought to test whether dogs eat plants and herbs in order to vomit because they have an upset stomach, or if they do it to supplement their diet because due to nutritional deficiencies. The initial study consisted of a survey of 25 veterinary students who owned dogs. They all said their dogs ate grass. None had noticed any signs of illness before their dog consumed the grass, while just 8% reported that their dog vomited frequently after eating grass.

Having revealed such results, the researchers decided to move ahead with the study and selected a sample of 47 canine owners. Of these, 79% said they had observed their dog eating plants (mostly grass). Only 4 of those interviewed stated they’d noted signs of discomfort in their dogs before they consumed the grass, and only 6 said their dogs had vomited after ingestion.

After these two preliminary studies, the researchers decided to continue their study and expanded the sample to 1,571 dog owners. Once again, 68% reported that their dog ate grass frequently. Only 8% said they had noted signs of sickness before the canines ate grass and only 22% indicated that their dog vomited after eating it.

The study concluded that most dogs eat grass and that this constitutes normal behavior. Also, in general, this behavior is not associated with any illness or upset stomachs. In other words, they do not perform this behaviour in order to purge because they feel unwell, or want to expel something that’s bothering them from their stomachs. It does appear, however, that in those dogs which present signs of illness prior to eating grass, the vomiting reaction is more common-place.

The study also found no evidence to support the theory of dogs eating grass to fulfill a nutritional deficiency, because the dogs which were given an additional plant-based supplement in their diets (vegetables or fruit) showed no more motivation to eat grass that those fed a diet without said supplement.

Another factor to highlight from the conclusions of the University of California’s research is that, apparently, younger dogs more commonly eat grass than older ones. Younger dogs also less frequently show symptoms of illness before eating grass, and vomit less after its consumption.

Dogs have inherited grass consumption from wolves, but they also enjoy it

Researchers have concluded that dogs’ consumption of grass could be a behavior that reflects an innate predisposition inherited from wolves. It seems that, in wolves, grass intake can act as a method of purging to eliminate intestinal parasites, for two reasons:

  1. The plant material helps to drag the worms through the intestinal tract.
  2. The fiber contained in the grass increases intestinal contractions, in turn contributing to said drag.

Although nowadays most of our dogs are parasite-free, it is possible they maintain this innate predisposition to eat grass – inherited from wolves – as a method to eliminate intestinal worms and other parasites.

However, one of the most accepted explanations as to why do dogs eat grass is that they simply like the taste or the relaxing effect of sniffing out and selecting a stalk then chewing it.

That’s why puppies and young dogs, more curious and exploratory by nature, perform this habit more often than older dogs.

However, according to veterinarian Michael Goldberg, of Hudson Place Veterinary Clinic in Vancouver (Canada), there is another alternative explanation:

It may be that dogs eat grass in imitation of what their ancestors, the wolves, do to disguise their body odor when they go out hunting. Similarly, many dogs like rolling in rotting animal carcasses and other odorous remains.

Why do dogs eat grass – Here are 5 reasons:

Sorry to disappoint you a little … The real truth is that nobody knows for sure why do dogs eat grass.  Humans have observed dogs doing this, and then made a few hypotheses to try to explain such behavior, but different sources give different explanations – often contradictory among themselves. So let’s apply a little common sense to check the possible reasons suggested in the canine world as to why dogs eat grass:

1. Why do dogs eat grass: Dogs eat grass to purge

This is the traditional reason, the explanation we’ve been hearing since we were kids. It’s said that if a dog has an upset stomach or has eaten something that makes them feel uncomfortable, the dog will eat grass “to purge”, i.e, to induce vomiting and thus rid themselves of the discomfort in their stomach or guts.

In other words, dogs eat grass as a natural remedy for their upset stomach, causing vomiting and the eventual expulsion of the substance that causes them discomfort in the first place.

But clearly this is not the only reason, because dogs that feel fine also seek and eat grass.

2. Why do dogs eat grass: Wolves also eat grass

This is a fact: wild wolves and other large predators (cats included) also consume grass. If we pay lip service to this fact, dogs’ consumption of grass isn’t an exhibition of neurotic or “weird” behavior, but simply a behaviour inherited from their ancestor, the wolf (the same goes for them spinning around the floor before bedtime). Instinct is wise, and this innate habit, present in both dogs and wolves but not yet understood well by us humans, is etched in their genetic memory.

3. Why do dogs eat grass: Dogs enjoy the taste of grass

Dogs eat fruit and lettuce on occasion (my dog for example, likes to eat lettuce and cucumber without dressing). The only reason dogs eat vegetables is because they like their taste and consider them to be beneficial. It’s pretty obvious that when we do something, it’s usually because we like it and feel good when we do it (and dogs are no exception!).

Dogs generally don’t just eat any weed that crosses their path, they have preferences. The Husky I spoke about at the start always looked for the newest shoots of a specific tall grass growing outside our house. He seemed to like that grass in particular, for its smell and flavour I presume, and always went looking for it. The truth is that he almost never vomited afterwards, and somehow it seems that this consumption of grass was good for him, or at least, didn’t give him any problems.

4. Why do dogs eat grass: Dogs who are hungry usually eat more grass

And so it is, grass is rich in fiber and while dogs seem to like the taste of plants, the fiber itself means the grass has a satiating effect. It is therefore logical that a hungry dog is more likely to try to fill its stomach and satisfy this hunger … even with weeds.

Human diets seek the same effect, and include high-fiber foods for this reason. Because we want to reduce the calories consumed on a daily basis, and in order to not feel hungry, diets increase fiber intake to “swell” our stomach and replicate the feeling of being full.

5. Why do dogs eat grass: Dogs eat grass to supplement their diet

This is another theory. We know a lot about dogs’ nutritional needs, we know how much protein or carbohydrates they need each day, but do not know everything.

Since we do not know exactly all the nutrients and trace elements dogs require to be healthy, it could be that the occasional consumption of small amounts of grass supplies certain vitamins or minerals needed in the dog’s diet in very small doses (and which the dog can’t get from the regular food you give them).

Also, faced with a particularly monotonous diet (eating dry food or biscuits every day), the dog gets bored and seeks a range of flavors.

Furthermore, eating just one single type of food impoverishes the dogs’ intestinal flora. As a result, grass would be a natural food supplement for your dog, which he himself opts to eat from time to time, to obtain certain plant-based benefits.

Is it bad that dogs eat grass?

There is no evidence to say that eating grass is bad for dogs, in fact, arising from a natural and instinctive behavior, in general we can say it is good for dogs to eat grass occasionally. Whether it’s to purge, to enjoy the flavor or to supplement its diet, instinct knows best and dogs – and animals in general – know what they’re doing.

However, you should monitor your dog and take care in certain cases:

  • Toxic plants:   There are some plants which are toxic to dogs. For example, never let your pet eat tomato plant leaves or green tomatoes, because these are particularly toxic to them.
  • Pesticides:   Depending on where your dog “grazes”, weeds or grass are likely to carry pesticides that cause diarrhea and physical discomfort. Exercise common sense and take your dog to safe places where you know that pesticides aren’t used. Be alert to this possibility to avoid poisoning!
  • Your dog eats grass excessively, compulsively:   In this case it would no longer be classified as a normal habit. If your dog eats grass compulsively (ie, gorges itself on as much grass as it can, or eats it every day or every time it has the chance, but you feel it has developed an  obsession or “fixation” with eating grass, then take it to the vet and explain the situation. It could be that your  dog   has dietary problems or perhaps “psychological” or behavioral problems (perhaps it suffers from stress or anxiety and this is their way to counteract it). In such cases your trusted veterinarian is your best ally!

Should you let the dog eat grass or stop it from doing so?

Paraphrasing the words of vet Adrian Aguilera, although eating grass has no reason to be problematic for a healthy dog, it’s a good idea to take certain precautions.

“In general, do not be alarmed when a dog eats grass; likewise there’s no reason to stop them. However, an animal which is trying to induce vomiting to expel a foreign body might end up making things worse for himself. Most often this behaviour is counterproductive because it only serves to produce gastritis.  If a dog with stomachache consumes grass, it will only make matters worse.”

At other times, the risk arising from a dog eating grass is that it may eat something poisonous, or a plant that has been sprayed with toxic fertilizer.

Has this post about why dogs eat grass been useful for you? If your dog also exhibits this behaviour and you have any experience or information you’d like to share, then tell us about it in the comments below!

6 COMMENTS

  1. Your article is really interesting. In my case, I had to take one of my female dogs to the vet because her feces were often really soft and sometimes had blood in them, as well as residues of grass; apart from that she has problems with really stinky gas, so I decided to take her to the vet and when he examined her, his diagnosis was that she simply shouldn’t eat grass because it’s bad for her, although it doesn’t happen to every dog. He also told me that dogs are not cows! He prescribed some pills for the diarrhea and bleeding, plus a special food for dogs with gastrointestinal problems and more specifically, he told me to give her the prescribed food (which isn’t cheap!) and nothing else. Not even mixing it with chicken , meat and cooked rice, which is what I prepare for my other canine babies.

    I’d like to know your opinion in this case.

    Thanks.

    • Hi Elizabeth, to know what is wrong with your dog you’d have to do some analytical tests. For example, the fetid gases, blood and diarrhea are symptoms of clostridium (a microscopic parasite not visible to the human eye, nor the vet’s microscope). How do you know if your dogs have this, or another parasite like this? By doing a stool analysis in the laboratory. It can be cured with specific antibiotics taken over a week, or two in the most serious cases.

  2. Hello Tami, I wanted to know if you can help my dog… today my dog began eating every plant it finds, wood, stones, everything it comes across, and then vomits. I want to know what causes this. Thanks alot for your help.

    • Hello Linda, it ‘s best to take your dog to the vet if it has suddenly begun to eat all these inedible items. This could be down to many reasons, from a serious disease or simply some nutrient deficiencies, parasites, behavioral problems, stress or lack of exercise.

      Point 5 is closest to the real reason why dogs eat grass. The “food” produced to feed them is dead food, containing no digestive enzymes as contained in natural food, which in the case of dogs – a carnivorous animal – should be all types of raw fresh meat.

  3. Hey Tami, you’re right that the monotonous diets that many people give their dogs are destroying their digestive systems. Then they turn out to be allergy sufferers, intolerant to many foods, with chronic diarrhea, etc etc.

    Is it good for dogs to eat ham? I have a Spaniel and when he eats ham he gets sick with gastroenteritis

    • Yes, ham is perfectly suitable for dogs to eat. However it shouldn’t be their only food. Your dog probably has intolerance, but you can also feed him chicken, and other things. Take a look at our recipe section, we have many different ideas.

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