Some people think dogs eat grass when they have an upset stomach. Since grass is not very digestible, many dogs do vomit after eating it, but this is not always the case. Some canine grazers show no sign of gastric distress before or after eating grass, while other dogs always vomit after munching on grass. Do those dogs eat grass because they already have an upset stomach and they want to vomit, or do they vomit simply because the grass upsets their stomachs? That's a question with no clear answer.
Another common explanation is that dogs eat grass to make up for a vitamin deficiency or a lack of roughage in their regular diet. It's unlikely that eating grass will actually add any essential nutrients to a dogs diet, and many healthy dogs who always eat a perfectly balanced diet also eat grass.
Most veterinarians agree that dogs eat grass simply because they like the taste
Eating grass is not a sign of illness. If, however, there are signs of ill health such as excessive vomiting, vomiting not associated with grass eating, loss of appetite, diarrhea, weight loss, lack of energy, or any other symptoms of illness - call your veterinarian.

