Why do dogs 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 deficiency in their diet.

In order to test these hypotheses, veterinarians* at the University of California-Davis vet school designed surveys to question 1600 pet owners. The results showed that:

• 80% of healthy dogs with access to plants had eaten grass or other plants
• 68% of responders stated that their dogs ate plants daily or weekly
• Only 8% of dogs exhibited signs of illness prior to ingesting plant material
• Only 22% of dogs vomited after eating plants

Dogs showing signs of illness before eating plants were more likely to vomit than those who appeared healthy beforehand. Younger dogs were more likely to eat plants, but less likely to appear ill prior to eating or vomit after eating the plant material. So 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 similar study is ongoing with cats. 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 help remove intestinal parasites from the GI system of wild dogs and cats. Our domesticated pets may have simply inherited this instinct. Dogs who appear ill before eating grass should be examined by their vet, especially when the lawn has been treated chemically.

All of the above is about actual grass. It is important to remember that there are some very toxic and deadly plants commonly found indoors and outdoors. They include tulips, oleander, hyacinths, poinsettias, sago palms, azaleas, lilies, and amaryllis. Pet owners should exercise extra caution when pets are near these plants.

*KL Chieko Sueda, BL Hart and K Davis Cliff. Characterisation of plant eating in dogs. Applied Animal Behaviour Science 2008, Vol 111, N 1-2, p. 120-132.