When you search the internet, you will find that the most common hypothesis is indeed that dogs intentionally induce vomiting to clean their stomachs. Your furry friend won't stick a finger down its throat, so it needs some other stimulus that leads to the evacuation of the stomach when it doesn't feel well for some reason. This is the first of the theories, which sounds quite logical and there may be some truth to it. But why would it do this, for example, after eating something it normally likes? And why does it usually not even look like it's feeling unwell when it goes to the lawn to "finish off" and relieve itself? Do dogs eat grass because they need to vomit, or do they vomit because they've eaten grass? And what about dogs that graze on grass as if it were a luxury salad but do not vomit at all? Something just doesn't add up here, raising the question of whether stomach cleaning is really what your furry buddy is after...
Surprisingly, there aren't many scientific studies that deal with this topic. One interesting study was conducted in 2008 at the University of California by a team of researchers (Karen Sueda, Benjamin Hart, and Kelly Cliff) and published in the journal Applied Animal Behavior Science. This study involved a series of surveys aimed at determining whether most cases of pets chewing grass are caused by some health issue or nutritional deficiency, and whether this activity usually leads to vomiting.
The initial study was based on a survey of 25 veterinary students who owned dogs. All students reported that their dogs eat grass. None of them confirmed noticing any signs of illness or discomfort in their pets before they started eating grass, and only 8% of participants said their dog vomited after "grazing." The researchers then conducted a second survey that involved 47 dog owners. They confirmed the fact that eating plants (mainly grass) is a common phenomenon, with 79% of them observing this activity in their pets. Other findings from the interview based on previous observations confirmed again that dogs rarely show signs of discomfort before eating grass (only 4 individuals) and vomiting also occurred minimally (only 6 dogs). After these two initial studies, the researchers expanded the number of study subjects through an online survey among 1571 dog owners. It was confirmed again that most of the respondents' pets ate grass regularly, with few showing signs of discomfort during it, and only just under a quarter reportedly vomited after the grassy meal. The researchers also found that it was mostly younger dogs that consumed grass, with no negative reactions appearing in them.
What follows from this? That the most widespread explanation popular at least since the days of our grandmothers, namely that dogs eat grass to vomit and thereby clean their stomachs, is likely not true. The finding that grass is more often eaten by puppies and younger dogs could be a sign of another widespread explanation, namely that dogs do it out of boredom, whim, and curiosity. This is, of course, also a tendency that puppies generally have.
Another popular explanation for grass eaters is the assumption that they are compensating for a certain nutritional deficiency. In other words, something is missing from their diet, and they go out to supplement it themselves so their bodies do not suffer. Logically, it suggests that this missing something should be plants. It could be due to certain nutrients not contained in a meat-based diet, or simply due to fiber, which meat does not contain nearly as much as plants.
There are cases of dogs that regularly ate grass (even though they might have vomited regularly afterward) until they were given food with a higher content of plant-based ingredients (or fiber). After that, they no longer thought of grass and had no need to compensate for any deficiencies. On the other hand, there are also studies that find no correlation between the increase of plant-based ingredients in a pet's diet and the decrease in the need for consuming grass and other plants in nature.
Probably the second most common answer given by various sources is that dogs evolved from wild canids, such as wolves, and follow behaviors according to their genetic blueprint. And here we slowly get to the crux of the matter. Well, okay, but isn't a wolf a pure carnivore? It is, and it does not have a strong preference for grass and other plant-based foods. However, it eats herbivores like rabbits, mice, or wild game, which have full stomachs of plants. And because wolves eat their prey almost entirely, they also take in the herbs from the digestive tracts. Thus, a wolf needs not only meat for good health but also plant-based components in its diet, which it obtains indirectly in this way.
It seems that the most reasonable explanation, which may initially seem a bit defensive, is that dogs do it simply because it's in their genes. Perhaps it's a predisposition they inherited along with their wolf DNA. Although it remains mainly a theory, it has a solid scientific basis and could be a real explanation for this mystery. When the composition of wolf droppings was examined, clear traces of plants consumed by wolves were found in 11-47% of the feces. So even if the wolf is a pure carnivore, it consumes some plants directly. However, this is for health reasons, not for nutritional ones. It has also been further demonstrated that grass consumption helps canids rid themselves of intestinal parasites. When plant-based, fiber-rich food passes through the intestines, it forces the organ to have greater contractions. Worms and other parasites that have infected the digestive tract attach themselves to the passing material and leave the body. Thus, grass can also help your pet. It is true that nowadays, when there are many effective methods aimed at parasites, most pets no longer suffer from such problems. However, it could be precisely this genetic habit originating from wolves, which has no other deworming option available to them besides the wild, natural one.
So when we put together everything we've said so far, there's some truth in all of it, and it forms a possible final explanation. Eating grass is likely a certain type of cleaning. Not in the sense of emptying the stomach through vomiting, but in a way that helps your pet rid itself of parasites through an increased amount of fiber. This would also explain why some dogs vomit after consuming grass. Grass simply isn't a natural component of their diet and is used for purely practical purposes of cleansing the intestine. So for your pet, grass may not be any tastier than it is for you, yet genes lead to its consumption. It seems that in most pets, an ancient gene wakes up from time to time that tells them to chase down some grass, even though they really don't need to.
So what should you do if your pet does not want to give up eating grass? When you buy it balanced food that includes quality plant-based ingredients in the form of vegetables, fruits, or herbs, everything should be nutritionally fine. Sometimes it's also helpful to supplement its diet with cooked vegetables that it likes. You will see if it craves grass less afterward. However, if it still indulges occasionally, you don’t need to worry too much about it. Researchers generally conclude their studies with the statement that this is a common behavior of domestic dogs that is not associated with any health problem or nutritional deficiency. But if you feel that it is overindulging in grass, of course, it is better to consult a veterinarian. The last thing you should really watch out for is to ensure that the lawn from which your dog "supplements" is clean and not sprayed with any chemicals, for example, pesticides. So know that if your furry friend has an urge to eat grass, it probably has just awakened its primordial wolf gene!
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