April 23rd, 2019
April 23rd, 2019
Why Do Dogs Eat Grass? (According To Published Studies)
April 23rd, 2019. Last Updated June 11th, 2020
Table of Contents
Is your dog chomping away at grass again?
And, God forbid, do they barf it all back on your carpet floor?
Whether your pup is wandering about in your lawn, or you’re out for a walk in the local park, you may have noticed that they particularly like eating grass.
Why do they do it? And is eating grass unhealthy or dangerous?
It’s apparent that dog owners are concerned. Many sources list “why do dogs eat grass” as one of the most common dog-related queries on Google.
In this article, we’ll examine two pieces of scientific literature on this topic to dispel common myths on grass eating, and offer three more likely explanations. And if you’re frustrated at your dog’s habitual grass eating, we’ll offer you ways to try and discourage this behavior moving forward.
Why Do Dogs Eat Grass? Popular Claims
There are many attempts to explain this behavior by veteran dog owners, Internet bloggers, professional veterinarians, and canine researchers alike.
Among the most common and popular of claims are the following:
- Your dog has a dietary deficiency, and is trying to make up for it by ingesting grass
- Your dog has gastrointestinal upset, and is trying to self-induce vomiting
- Your dog is trying their hand (paw?) at self-medication, by trying to cleanse their gastrointestinal organs of parasites.
Let us know if you’ve heard these answers before.
Now, while the scientific literature out there is scarce, some exists. And that means we have some data that we can use to either prove or disprove each of these theories.
The Science of Dogs Eating Grass
Let’s jump headfirst into what we know about the science of dogs eating grass.
While researching this topic, I found that many sources eventually led back to two frequently cited studies.
Study #1: Grass Eating Patterns In the Domestic Dog, Canis Familiaris
Interested in the full study? Find it here.
Our first study was done by researchers at the University of New England in 2009 by experts in psychology and animal science.
The study focuses on a sample size of 12 mixed-breed dogs, all of whom were raised by the same owner. And all of them exhibited behaviors of eating grass.
These dogs were brought into the research facility, and put on the same routine and diet for 7 days, after which the experiment would begin. This was to get the dogs accustomed to the routine first.
The diet was a nutritionally complete and balanced commercial kibble.
During the first two days of the experiment, the dogs were fed a meal at 9AM, and presented with grass at 9AM, noon, and 3PM. 6 dogs had access to the grass before the meal, and 6 dogs after.
Grass eating activity was recorded.
During the next two days, the dogs were again presented with grass at the same 3 times, but were fed at 12 o’clock noon instead.
Ditto for the final two days, where the dogs were fed at 3PM.
Goal of the Study
The study intended to answer two main questions (actually, it was three, but we are only interested in two of them for the purposes of this article):
- Is grass eating influenced by satiety (i.e. hunger)?
- Is grass eating influenced by time of day?
Results of the Study
After the six days, researchers tallied up various statistics regarding the dogs’ encounter with the grass. One stat we are particularly interested in is time spent eating grass.
The study found that dogs who did not get to have their meal yet spent significantly more time eating grass than dogs who already ate.
This seems to heavily indicate that dogs who are hungry will naturally tend to eat more grass. That’s intuitive enough!
Secondly, since vomiting had been linked with grass eating, researchers gave special attention to any vomiting episodes that occurred.
In the 6 days of testing, there were only 5 vomiting episodes.
Based on this, the natural conclusion is that dogs do not seem to ingest grass to purposefully induce vomiting.
Finally, researchers indicated that dogs spent significantly less time eating grass in the afternoon (at 3PM) than during the morning (9AM) and noon testing sessions.
Hunger and familiarity probably played a role here. By the afternoon, the dogs had already had enough grass and didn’t want to eat more.
Thus, I think it’s inconclusive to say that time of day influences grass eating. At least, it doesn’t play as much of a role as simple hunger does.
From this first study, we drew the following conclusions:
- Hunger influences grass eating behaviors.
- The idea that dogs eat grass to induce vomiting was not supported by this study.
- Time of day may or may not have had an influence on grass eating.
Before we move on to the next article, I also would like to point out that the sample size of this study is relatively small (only 12 dogs were examined).
However, it still takes a scientific approach to studying grass eating behavior in dogs, which is a rare find. We ultimately trust this source as one of the few that provide real experimental data on this topic.
Study #2: Why Do Dogs And Cats Eat Grass?
Interested in the full study? Find it here.
Our next study was authored in 2008 by Benjamin Leslie Hart, DVM, PhD, DACVB from the University of California, Davis.
Compared to the last study, this one doesn’t involve a strictly scientific approach. Instead, it aimed to survey a wider range of dog owners about grass eating behaviors in their dogs.
So whereas the first study gave us a glimpse into the behaviors of 12 dogs, this one will give us a more representative picture of the average grass-eating dog.
That means this study will complement the data we got from the first study well.
Researchers in this study sent a Web-based survey out, targeting dog owners with dogs who were known to eat grass.
More than 3,000 owners responded to the survey, and researchers collected data about the dogs’ grass-eating habits, diet, sex, breed, and age.
Goal of the Study
At the very top of the study, three large headlines are presented which we re-word as questions here, to define the goal of the study:
- Are dogs that actively eat grass sick, and do it to induce vomiting?
- Do dogs eat grass to make up for a dietary deficiency?
- If not one of the two above factors, what can other studies tell us that lead us to the correct answer?
Results of the Study
Of the 3,000 responses, researchers filtered out responses from dog owners who spent less than six hours a day with their dogs, and dogs who seemed to only chew but not ingest plants. This brought the total survey sample to 1,571.
Statistics-wise, the study found that:
- 68% said dogs eat plants regularly (daily or weekly basis)
- A mere 8% said their dogs had previously shown signs of illness before eating grass
- 22% reported that their dogs vomited regularly after a grass eating event
From this data, we can reasonably conclude that illness doesn’t seem to invoke grass eating. However, we note that “signs of illness” in this case is rather vague, and it’s unknown if certain specific conditions will make it more likely for a dog to eat grass.
In addition, as only 22% of dogs vomited regularly, it only bolsters the conclusion from the first study that dogs do not eat grass to purposefully induce vomiting.
There were a number of other very interesting conclusions drawn by this survey.
Firstly, younger dogs seemed to eat grass more frequently than older dogs. Younger dogs were also less likely to appear ill beforehand, or vomit afterward.
The study suggests that this is driven based on ancestral biology. Wolves and cougars reportedly ate plants to purge intestinal parasites.
As a result, one plausible explanation is that younger dogs are not as resilient to parasites, and thus eat more grass to protect themselves. The study calls this herbal prophylaxis.
Whether or not the dogs are actually eating plants for this reason has yet to be proven, but the biological context is certainly there.
Secondly, the study tried to link diet with grass eating. It turns out there was no definitive difference in grass eating patterns between dogs that ate raw food compared to those on a commercial diet.
Moreover, even dogs that ate less fiber did not show significantly different grass eating behaviors.
From these two points, it appears that dogs do not eat grass to make up for any particular dietary deficiency.
Dispelling Common Myths
Let’s take a look back at the common claims we were presented with at the beginning of the article.
Myth Or Fact #1? Dogs Eat Grass To Make Up For A Nutritional Deficiency
At least based on our studies, this appears to be a myth. No evidence has been shown so far to support this claim.
“But aren’t dogs omnivores?” you might ask.
It’s true that dogs, like their wild canid ancestors, are omnivores.
However, good commercial and raw diets do actually feature vegetables as secondary ingredients in their balanced formulas. So the idea that a specific nutritional deficiency is the culprit for grass eating doesn’t seem to hold water.
Myth Or Fact #2? Dogs Eat Grass To Induce Vomiting
Based on both of our studies, this is a flat out myth. There doesn’t seem to be a direct link between eating grass and deliberately inducing vomiting.
Myth Or Fact #3? Dogs Eat Grass To Self-Medicate
This last one is a little more murky; it may or may not be true. Biologically speaking, our dogs’ ancestors did appear to have a history of eating plants to wash out parasites.
But whether this is true in our domesticated dogs is yet to be seen, given that as dog owners, we actively bring our dogs to the vet to get rid of intestinal parasites ourselves.
In any case, since our studies have not actively disproven this, we admit it as a possible cause for grass eating.
Speaking of causes for grass eating, let’s jump into that now.
So Then, Why Do Dogs Really Eat Grass?
We’ve just cast some serious doubt on some long-accepted theories for grass eating in dogs. By now, you’re itching to know… why do dogs really eat grass?
Cause #1: Your Dog Likes The Taste.
… So you’re telling me, we dove deep into two studies just to arrive at this simple conclusion?
Unfortunately, I’ll admit, “your dog eats grass because they like it” is a pretty unsatisfactory answer.
But here’s a fact: your dog likes exploring the world with his mouth. Dogs put things in their mouths all the time.
They do this to feel and taste the object. For puppies, sometimes putting an object in their mouth (and sometimes, swallowing it) is the only way to find out what is edible and what is not. Talk about learning a lesson the hard way!
So if your dog has tried eating grass once, and still chooses to come back for more, it’s not hard to fathom why your dog is eating grass: he probably just likes the taste!
Let’s continue to beef this answer up with some veterinary terminology.
Pica in Dogs - Eating Non-Food Items
Dogs eating grass falls under the category of pica in dogs. Pica is a condition where your dog ingests non-food objects.
This includes furniture, cardboard, paper, rocks, garbage, metal, plastics, anything really… even their own feces.
You could make the argument that grass is actually an edible food–after all, it’s a staple for other animals like cows. However, since we don’t ever feed dogs grass on purpose, it still qualifies as pica.
Pica is not uncommon in dogs. After all, dogs use their mouths to interact with the world all the time.
A lot of dogs will jump at the chance to eat, well, anything really.
And if they repeatedly show behavior of putting grass in their mouth, it’s reasonable to conclude that they simply enjoy the taste of it.
We know it’s not the most satisfying answer, but perhaps that is one of the best causes for eating grass that we know of.
Cause #2: Your Dog Is Bored.
We know that dogs can eat grass frantically despite being fed a full, balanced diet. So perhaps it has to do with boredom more than anything else.
While some dogs are perfectly content spending the day doing nothing (Yuna is one of them), others need more mental stimulation.
Lying around all day is sure to get boring after a while. Lack of stimulation and/or exercise is a common reason why our dogs start engaging in unwanted behaviors. One of them is grass eating.
You may not be spending enough time playing with your dog. Or, you may not be giving your dog enough exposure to new experiences both in and out of the house. Maybe you’re not exercising your dog enough, period.
Boredom in dogs has many causes. And you will clearly see its effects, in the form of chewed up furniture, dug-up trash, or a significant increase in grass eating.
The good news is, it’s relatively easy to fix this. Generally spending more time with your dog doing more new, engaging activities, or simply just buying them a couple new toys to gnaw on could keep them from wandering out to the lawn for entertainment.
Cause #3: Dogs Eat Grass To Self-Medicate
As we discussed in the studies above, we admitted the possibility that dogs eat grass to self-medicate.
This was primarily due to existing biological evidence that our dogs’ ancestors seemed to voluntarily ingest plants to clear parasites.
Is Grass Eating Problematic?
Now that we’ve outlined three of the most likely causes for grass eating, let’s address all the concerned dog owners out there.
Here’s the one final conclusion that was drawn by both studies we looked at: eating grass is normal behavior.
If your dog eats a few blades of grass weekly, or even daily, this isn’t a big concern, particularly if your dog shows no ill-symptoms before and after.
Hopefully that settles most dog owners out there!
But My Dog Is Eating Grass AND Vomiting. Should I Be Concerned?
It may be a different story if your dog starts ingesting large amounts of grass, and/or vomits frequently afterwards.
First of all, if you notice this, stop letting your dog have free access to grass. Bring them outside on a leash (even if it’s just your backyard).
Do not let them eat any grass for a few days. If they stop vomiting as a result, then there shouldn’t be too much cause for concern.
But if the vomiting continues, perhaps it’s indicative of something else going on with your dog. Your vet may choose to conduct a fecal float test and blood test to check for a gastrointestinal disease.
Additionally, if your dog vomits nearly every time after eating grass, check with your vet for any poisoning.
Many lawn care items can contain ingredients that are especially poisonous for dogs. Be careful with any pesticides or products you use to maintain your yards.
Finally, I will note that allowing your dog to develop the habit of ingesting yard plants is generally not good. There are many common garden flowers that are poisonous to dogs as well.
So in general, though eating grass itself in reasonable quantities is not cause for alarm, finding ways to curb this behavior is desired.
How To Stop Your Dog From Eating Grass
So what are some ways to try and discourage grass eating?
The most straightforward way is to just keep a closer eye on them, and have them on leash when they’re near grass.
That way, you can prevent them from eating grass on a moment’s notice.
Going back to cause #2 where we brought up boredom, maybe your dog needs more stimulation from you.
Give them some extra one on one interaction a day, and see if this translates into less grass eating, and maybe even other destructive behaviors too.
Adding Vegetables To Your Dog’s Diet… Does It Help?
While we dispelled the myth that eating grass is to make up for a nutritional deficiency, we made this conclusion because of the lack of evidence out there.
This doesn’t mean that we weren’t willing to turn Yuna into a guinea pig here. We tried introducing more roughage (food high in fiber content) to her diet to see if that would influence grass eating.
Sources suggest that since grass is cool, fresh, and textured, good veggie substitutes would be carrots, peeled celery and lettuce.
Steaming these veggies without any seasoning and adding them to your dog’s diet is also just a great health booster.
At least for Yuna, even after introducing more steamed veggies, it didn’t seem to significantly discourage her from eating grass (even though she didn’t eat much grass to begin with).
But with the multitude of dog owners out there preaching support for this, we thought we’d leave it up to you to try.
Besides, there’s no possible way to lose here. Your dog gets an excellent fiber boost in the worst case, and perhaps even stops eating grass in the best case.
Finally, some dog owners even suggest buying a small tray of grass just for your dog or even starting an indoor herbal garden! The benefit to this is that you control their grass intake and eliminate the possibility of them ingesting any poisonous lawn care chemicals.
So why do dogs eat grass? We have given a couple possibilities in this article, and also dispelled some common myths out there.
We eagerly await new, fresh research on this topic!
Grass eating is perfectly normal behavior in dogs. But that doesn’t mean we shouldn’t be alert.
Perhaps the old adage of “going with your gut feeling” applies well here–if you think something is wrong, it probably is. Any abnormal or extreme grass eating (and vomiting thereafter) should be brought up and examined by the vet.
Does your dog eat grass? Tell us about your experiences!