Dogs eat grass for a variety of reasons, not all of which is to vomit. I have two that like to graze on a certain type of grass as though it were a delicacy. This grass does not irriate their GI tract and they never vomit but they love to chew on it when they find it (which is hard in Arizona).
I also have one dog in particular (though the others also experience on the rare occasion) that gets an upset stomach - especially in the morning after an overly long fast (in otherwords after I have slept in and his meals are spaced longer than 12 hours apart).
He will go out and chew a very fibrous and almost prickly long bufflegrass that definitely irritates the GI tract and makes him vomit. His upset stomach is most likely due to the bile acids that accumulate in his stomach in preparation for food. When the food is not forthcoming and his stomach is static - the acid just sits there like sludge and makes the dog nauseous. The older he gets - the more this can occur due to the more static his stomach becomes as he ages.
There are a couple of things that help 1) do not let your dog have an overly long fast period. I try and give large cookies at bed time and this usually helps 2) talk to your vet about motility drugs such as metoclopramide (Reglan) that helps the stomach to regularly empty itself whether food is present or not - this can keep bile acids from accumulating and making the dog feel bad - you can just use at night if the morning seems to be the time he feels nauseous 3) if you have an alternatve vet who uses Standard Process Whole Foods Nutrional products - ask them about the use of Choline. This product worked wonders on my guy in addition to not letting him have an overly long fast - which is hard to control sometimes.
If this continues, never consider it "normal" - it is not normal to feel nauseous repeatedly every couple of days - therefore it is never wrong to get a full blood panel work up - esp. now that he is 8 and considered geriatric. It is always good to have base line values in which to compare as he gets older but you might be able to catch something early.
Good luck.
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