Why is my dog eating grass?

One of the most common questions at veterinary hospitals is “Why does my dog eat grass?”  Urban legend states that pets eat grass because they “know” they are sick and need to vomit or that the pet is aware of some dietary deficiency.

In order to test these hypotheses, veterinarians at the University of California at Davis School of Veterinary Medicine designed surveys to question pet owners about their pets’ grass eating habits.  Dr. Karen Sueda, Dr. Kelly Cliff, and Dr. Benjamin Hart conducted the study which was funded by the Center for Companion Animal Health at UC Davis.

An initial survey of owners of healthy dogs found that 80% of dogs with access to plants had eaten grass or other plants.  The study also surveyed dog owners about their dogs’ plant eating habits, the dogs’ diet, and gathered information about breed, sex, neuter status, and age.

More than 3,000 pet owners responded to an extensive online survey.  Of these, almost 1,600 surveys were considered to be usable.  About 68% of responders stated that their dogs ate plants daily or weekly.

Only eight percent of dogs showed signs of illness prior to ingesting plant material and 22% of dogs vomited after eating plants.

The survey also showed that those dogs showing signs of illness before eating plants were more likely to vomit than those who appeared healthy beforehand.

Finally, younger dogs were more likely to eat plants but less likely to appear ill prior to eating or vomit after eating the plant material.

The veterinarians concluded that in most cases grass eating is a common behavior in normal dogs and has no correlation with illness.   Additionally, most dogs do not appear to routinely vomit after eating grass.  

A study is on-going with cats and preliminary data shows that cats are less likely to eat plants than dogs.   Just like dogs, most cats do not routinely show signs of illness prior to eating plants and don’t regularly vomit afterward.

The researchers have hypothesized that plant eating may serve to help remove intestinal parasites from the GI system of wild canids and felids. 

This study is also published in Applied Animal Behavior Science, 111: 120-132.