Why does my dog eat grass?
While it's quite common for dogs to eat grass, little is known about the reasons why they do it. Although this question is often asked it's not really something the scientific community is doing much research on.
Some of the most listed reasons are:
According to this theory, a dog would eat grass because he doesn't feel well. By eating grass, he would start to vomit, this way solving his stomach problems. This does sound as a reasonable theory, however most dogs don't vomit after eating grass. According to a recent study in Applied Animal Behaviour Science (paywall) less than 22% of the dogs vomit after eating grass. This research did indicate however that if you dog is not feeling well, he is more likely to vomit after eating grass. Another study by the University of New England (pdf) put this figure even lower (less than 1%).
The study from the University of New England shows that dogs were more likely to eat grass before being fed. The more hungry a dog is the more likely it is that he will eat grass.
Nutritional deficiencies - mainly fiber
This theory seems to be supported by a case published in The Journal of Veterinary Medical Science . A miniature poodle which was eating grass and vomiting on a daily basis for seven years. After switching to a high-fiber diet this behaviour stopped.
Maybe you're dog is just bored and eating grass to pass time. Try to spend some quality time with your dog and provide sufficient mental and physical exercise.
Should I stop my dog from eating grass?
No. Most veterinaries and scientific studies indicate that grass eating is just normal dog behaviour. Eating grass is not harmful. You must be aware however that some pesticides and herbicides are toxic for dogs, especially when ingested.
While grass is harmless, some other plants can be toxic for your dog as well.