Why My Dog is Eating Grass ?

Veterinarians will tell you that they answer this question all day, every day which means lots of dogs eat grass. Eating “strange” non-food items (like grass) is technically known as pica and may be associated with a diet deficient in nutrients, vitamins, or minerals. But dogs on well-balanced, commercial diets should not be nutritionally deficient, so why do they eat grass?
Is eating grass a physical need?
One common assumption is that dogs eat grass to relieve upset stomachs. Some dogs consume grass with urgency, then vomit shortly afterwards. Here is the chicken vs. egg dilemma: Does a dog eat grass to vomit and soothe an ailing stomach or does he develop a stomachache and vomit because he ate grass? Since studies show that less than 25% of dogs vomit after eating grass, it is unlikely that they turn to the green stuff as a form of self-medication. In fact, only 10% of dogs show signs of illness prior to eating grass. The bottom line is that the majority of grass-eating dogs are not sick beforehand and do not vomit afterwards.