Scavengers - Dogs, unlike their catty counterparts, are not carnivores. But they are not your garden-variety omnivores, either. The modern dog, partly because of evolution and domestication, is no longer like its ancestors, which frequently ate their prey entirely. Instead, dogs today seek out plants as an alternative food source. Most commonly the plant is grass -- since that is what is closest at hand -- but wild canines are known to eat fruits, berries, and other vegetable matter, too.
Tummy trouble - A dog will seek out a natural remedy for a gassy or upset stomach, and grass, it seems, may do the trick. When ingested, the grass blade tickles the throat and stomach lining; this sensation, in turn, may cause the dog to vomit, especially if the grass is gulped down rather than chewed. Although dogs don't typically graze on large amounts of grass like a cow, they may nibble on grass, chew on it for a while, and not throw up (an unwell dog will tend to gulp the grass down in big bites and then throw up). This may be because they find the texture of the grass palatable, or just because they need to add a little roughage to their diet.
Nutritional Necessity - Whatever the reason may be, most experts see no danger in letting your dog eat grass. In fact, grass contains essential nutrients that a dog might crave, especially if they're on a commercial diet. If you notice that your dog has been munching away on grass or houseplants, then you may want to introduce natural herbs or cooked vegetables into their diet. Dogs aren't finicky like cats, but they're not too fond of raw veggies either. So, when you think about it, grass munching isn’t that bad at all. However, watch out for a sudden increase in grass eating; it could be a sign of a more serious underlying illness that your dog is trying to self treat, and that requires immediate veterinary assistance. Also, it is important to focus on the situations where grass eating should be prevented at all costs. The most important of these situations is when grass has been treated with any type of chemical. In most public parks and locations when grass has been treated with pesticides or other chemicals, companies are required to display warning signs so that pet owners can keep their dogs off the grass completely. Not only can dogs ingest these chemicals through eating the grass but they can also lick them off the pads of their feet after walking on contaminated grass. When grass has been treated with any type of chemical dogs should ALWAYS be steered away from the affected area. Pesticides and herbicides are noted for being one of the leading causes of pet poisoning that lands pets in the veterinarians office.