Dogs Eating Grass
How do dogs know exactly what grass to eat to make themselves throw up? - Steve
I'm ashamed to say that I can't really answer this question. Everywhere I turn is contradictory information & nobody has ever actually studied this topic. But I can share some of the current theories & you can probably pick the one that makes the most sense for your dog.
The American Animal Hospital Association has an article posted in their library on this topic, but it's very short & not overly informative. It states that "no one has ever proven dogs are intelligent enough to use grass as a medicinal herb" so medical professionals tend to believe that they eat grass simply because they like the taste & vomit because they've eaten grass.
I think this is an ignorant statement -- just because no one has proven it (or even tried to prove it) doesn't mean it's not true. Look at Copernicus, for instance: He couldn't prove his theory but the Earth does in fact revolve around the sun. Five hundred years from now, dogs could be publishing scholarly critiques of these "primitive" AAHA articles, for all we know now.
One good thing in this otherwise unenlightened article is that it contains a link to a survey you can take to explain your dogs habits. The University of California Davis School of Veterinary Medicine is currently conducting the first-ever study of grass eating in dogs & would like your input. Please take a few minutes to take the survey, it doesn't take long.
Many experts feel that dogs enjoy the flavor & texture of grass so they eat it. Our dogs' wild relatives (foxes, wolves, coyotes) eat their entire kill, which means that they are ingesting the stomaches of herbivores & indirectly getting a bunch of roughage in their diet this way. Domestic dogs may have an inborn craving for grass because of this.
Some dogs only eat grass that other animals have "marked", in this way erasing everyone else's scent from the area. If this is your dog's reason, it explains the choosiness of the selection & the fact that someone else whizzed on it could explain the barfing.
Theories abound about a lack of specific nutrients in the diet but research just doesn't support it. Even healthy dogs with well-balanced diets eat grass. And some dogs with less than perfect diest never eat grass.
Vetinfo.com has some interesting details on this topic, but no more information than you've just read. I say, that's even more reason to participate in the study, as it may help us to someday understand this behavior.