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‘Why does my dog eats grass’ and the possibility that pets can self medicate!








Why Does My Dog Eat Grass?


Why is it that every time my dog goes outside she eats a bunch of grass?  It’s funny to watch her in the process.  She selects the longest blades and then goes about the business of nibbling it down like some kind of canine sword swallower. Shortly thereafter, I hear her retching it all back up again: one medium-sized blob of green enshrouded in foamy white spit.

Four Theories Behind ‘Why My Dog Eats Grass’


Veterinary experts (including those of us here at Brookfield) have pondered the ‘why does my dog eat grass’ question for years.  Here are our four best guesses based on published research and our own observations.


It Tastes Good


Yes, the answer is that simple.  In a thread published on the Veterinary Information Network (VIN), the world’s largest forum for veterinarians, most vets agree that dogs eat grass because they like the taste.  They contend it is something that dogs have been doing for ages.   Modern day wolves, the evolutionary grandparents of today’s dogs, are used to eating the meat of herbivores as well as the contents of their stomachs.  Perhaps dogs have a left over taste in their mouths for the days when they were eating fresh caught rabbits that were stuffed with ingested grass. Long, fresh, spring shoots of grass are tender and have a pleasant taste.

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Your Dog Is Self Medicating!


The idea that dogs, or any other animal, may instinctively know what kind of medicinal plant to seek out when sick is called Zoopharmacognosy. Though the data around the idea is circumstantial, it is none the less compelling.  When deciding if an animal is self medicating versus just eating, the ingested food had to satisfy 4 criteria:


    • The food has little-to-no nutritional value
    • The food is not a typical staple in the animal’s diet
    • The food is only sought out at a particular time of year, for example at a time when intestinal parasite prevalence is higher
    • The food is eaten by only one or a few members of a larger group that otherwise abstains.


Examples of animals believed to self medicate include Madagascar lemurs that eat small amounts of tamarind and fig leaves and bark to increase milk production; elephants that induce pregnancy by eating the leaves of certain bushes; macaws that ingest clay to aid in digestion; and bonobos that consume the leaves of a highly irritating plant only during ties of peak parasite infection. It’s interesting to note that in all the countries where these plants exist, humans have turned to them as well for the same medicinal properties.


Is it possible that dogs eat grass because they feel ill and want to use the rough surface of the grass to help cleanse their digestive tract or to induce vomiting?  We’ve certainly seen enough incidences that give us reason to believe that the theory could be true.  It is not believed that the grass itself causes nausea, rather, the long blades of grass lodge in the throat, tickle, and induce a regurgitation response.


Nutritional Deficit


All animals eat what they eat because they have evolved to select the food right for their nutritional needs based on what’s available and when. Foraging behavior is also learned.  In the wild, mother chimps have been observed slapping the hand of a youngster reaching to eat the leaf of a plant that is not the normal staple of the clan.


Some veterinarians report that grass eating behavior stopped immediately once fiber was added to the pet’s regular diet or when the diet was switched to a different brand.  Unlike their wolf ancestors, dogs have a much better ability to digest carbohydrates, so its possible that dogs are extracting some nutrition from ingested grass (or any other leafy green for that matter), but we should note that dogs that eat grass often pass most of it in their stool undigested.


Habit, Hunger or Boredom


Some dogs, especially food driven breeds like Labs and Retrievers, are thought to go for grass because they’re crazy for food and it’s another thing that they can ‘wolf’ down. Some dogs may go for grass as part of a nervous eating habit or simply because they are bored.








What About Cats?

Cats too are believed to eat grass because it tastes good.  Both cats and dogs seem to favor long, slender blades of grass because they are young, tender, and presumably most tasty.







Can My Dog Eat Grass From a Lawn That’s Been Treated?


That’s an excellent question and one that’s especially polarizing.  Here’s more of what we know.


Are Lawn Chemicals Bad?  Depends on Who You Ask.


There are no lawn chemicals on the market that haven’t passed the scrutiny of government safety organizations like the EPA. Presumably, if used according to manufactures’ directions, they should cause pets no harm, but critics argue that the research in this area is typically conducted by the manufacturers themselves and may not be as exhaustive as it should be. At Brookfield, for safety purposes, we recommend that pets stay away from treated lawns for 24 hours unless otherwise specified by the product label.

Chemical Classes and Potential Side Effects


Chemicals used on lawns can be divided into four classes:  broad-leaf weed herbicides, soil amendments, pre-emergent weed killers, and pesticides.  As mentioned earlier, some authorities contend that lawn chemicals cause potential or proven health issues, but to date,  there is enough debate on the topic to allow their continued approval by the EPA and their use.  Below is a description of how the chemicals in each category work and the health problems that some insist are connected with them.


Broadleaf Herbicides


These chemicals inhibit the completion of photosynthesis in broadleaf plants or in some other way disrupt normal plant functioning.  Glyphosate, the active ingredient in RoundUp, is probably the most extensively used chemical in this group and may cause cancer, kidney problems, liver disease, or reproductive issues in humans.


Soil Amendments


These chemicals are applied to change the ph of the soil, the tilth of the soil, or to add nutrients. Chemicals that change the ph or tilth of soil, especially lime and organic material respectively, are mostly safe, but pets can become ill if they eat grass that has been recently fertilized. Additionally nitrogen, phosphate and potassium, listed on fertilizer bags as NPK, are known to leach into waterways where they increase algae growth and rob streams of precious oxygen.


Pre-emergent Weed Killers


These chemicals inhibit the production of enzymes in seeds necessary for plant emergence. The effects of long-term exposure to the active ingredients in these herbicides, especially the chemical 2,4-D, are hotly debated.




Of all the categories listed, the chemicals in this group pose the greatest risk to your pet’s health. Avoid exposing your pet to lawns recently treated with pesticides.  Know that, if ingested, lawn pesticides can sicken or kill your pet. Dogs or cats that eat grass that has been treated with a pesticide may get sick, but because both animals typically only eat a small amount, it is unlikely that the chemical will cause severe illness.


Risk of Intestinal Parasites


Intestinal parasites have evolved to use animals’ interest in eating grass to infect them.  After emerging from eggs deposited in the soil by previously infected animals, parasite larvae crawl up to the tips of grass blades where they wait to be eaten by a passing herbivore, dog,  cat, (or stepped on my a human).  Once swallowed, the parasites continue with their life cycle and reproduce in your pet’s digestive system.  Products like Proheart and Revolution protect pets against some of these kinds of intestinal parasites.


Why Does The Grass Die Where My Pet Pees?


Every wonder why the grass dies where your pet pees?  It’s because urine contains nitrogen, a chemical that in small amounts acts like a fertilizer, but in larger amounts kills plants.   It’s also why gardeners are cautioned to never fertilize with green chicken manure.  Chicken manure is very high in nitrogen because a chicken’s feces is mixed with its urine and the high nitrogen content kills plants.


Bottom Line


Your pet can safely eat grass provided it has not been recently treated with a chemical.  It is not uncommon for pets to vomit after eating grass, but pets that eat grass aren’t necessarily sick, they may be just bored, hungry, or like the taste of grass.  Dogs or cats under 5 pounds that vomit for more than 4 hours and all other pets that vomit for more than 6 hours should be seen immediately by one of our veterinarians.



Why does YOUR dog eat grass?  Have something to say about lawn chemicals and safety? Scroll to the bottom and use our comments section to share your opinion.


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