Why do dogs eat grass?

Almost all dog owners have seen man’s best friend graze on grass at one point or another. When my family first got our dog, we were completely perplexed as to why he would sit in the grass and chow down like a cow. A popular theory is that dogs eat grass to help with an upset stomach, but with my research I have found that this is a myth.

In this study conducted in 2009 and published in Applied Animal Behaviour, they found that grass eating behavior in the domestic dog may be related to gastrointestinal distress. This study observed grass eating behaviors in dogs fed a standard diet with and without supplementation of fructo-oligasaccharide (FOS), which temporarily induced a mild gastrointestinal disturbance. During both FOS diet and standard diet periods, dogs were presented with grass, and the time spent eating grass and the number of grass eating events was recorded. Researchers found that dogs spent more time eating grass when fed the standard diet than when they were fed the FOS diet. This suggest that dogs do not use grass to “self-medicate” a gastrointestinal disturbance.

In another recent study (2009) by Dr. Karen Sueda, Dr. Kelly Cliff, and Benjamin L. Hart, conducted three surveys of pet owners to find answers to these and other questions about plant eating in dogs. The first survey focused on twenty-five veterinary students who had pet dogs. They were asked about the frequency of grass eating in their own dogs and whether the students observed signs of sickness before grass consumption or vomiting afterwards. All students reported that their dogs ate grass, but none reported observing signs of illness before their dogs ate grass, and only 8% reported that their dogs regularly vomit afterward.

The next survey was a group of 47 dog owners that were asked for their observations of their pets’ consumption of plants and the animals’ behavior before and after. Of this group, 79% had observed their dogs eating plants, particularly grass, and thirty-three owners answered questions about their dogs’ behavior before and after eating plants. Out of these dogs, signs of illness were infrequent (four) and vomiting post-grass-eating was only occasional (six).

The null hypothesis (plant eating is not particularly related to illness or vomiting) was tested again with a large web-based survey with more than 3,000 owners responding. These owners were asked questions abut their dogs’ grass-eating habits and diet, and about their dogs’ sex, breed, and age. This is what they found: “Sixty-eight percent of the respondents said their dogs ingest plants on a daily or weekly basis,” “Eight percent of the respondents reported that their dogs frequently show signs of illness before plant eating,” “Twenty-two percent reported that their dogs regularly vomit afterward,” and “Of the plant-eating dog population, younger dogs ate plants more frequently than did older dogs and were less likely to appear ill beforehand or to vomit afterward.”

Contrary to the common perception that grass eating is associated with observable signs of illness and vomiting, this survey-based study found that grass eating is a common behavior in normal dogs unrelated to illness and that dogs do not regularly vomit after eating it.

After reading this and discovering that grass eating is a common and normal behavior with dogs, the only logical explanation left is that dogs may possibly be part cow.


3 thoughts on “Why do dogs eat grass?

  1. Andrea Marie Linn

    My dog would always eat grass right before she threw up. I think it had to do with something that would help her digest the food and ease her pain. I always thought it was gross and tried to stop her form continuing. Honestly, the way my dog acts now, I wouldn’t be surprised if she wasn’t part cow!

  2. Rachel M Arndt

    My dog eats grass occasionally and I found this article to be very informative! It was usually around a time when he was ill. He never did it too much and we talked to the vet about it at a check up. A lot of your facts make sense with exactly what the vet told us! This behavior is normal for dogs, but still strange to us as humans…

  3. Adair Mustafa

    It’s funny that I have always noticed my dog do this but I never knew why. This makes me wonder after hearing Mr. Mallouk speak in class if dogs eating grass could potentially have the same negative impact as cows do on our environment. We learned that the methane emitting cows contributed to the recent rise in temperature that we have all experienced. Here is an article explaining the problem


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