I call Princess 'poopy breath'. I try to brush their teeth about 3 x's a week & that smell is not there sometimes. It's almost like she burps or the smell is coming from somewhere else, like the op mentioned maybe intestinal gas? The strange thing is, when I open her mouth & smell it, the poop smell is not there, but when she kisses me, I can smell it.
The smell is different from icky doggy breath, it actually smells like poop like she just ate it. I know for sure she doesn't eat poop. Her teeth are white, except for a little tartar build up on her back molars. Although she does seem to have more teeth in the back...maybe they didn't remove all her puppy teeth?
Feb is 'Dental' month @ our vet's, so they're all going to have their teeth checked/cleaned. I'll find out then if she has any rotten teeth going on. She's only 2, I doubt it. Last time she had a check up, our vet didn't seem concerned of her poopy breath...hate it when they don't show concern & don't give me answers.
I feed mine Wellness Core, they love it & seem to be doing great on it. They were on Acana Grasslands, but I switched recently bc my local pet store didn't carry it...thinking of switching back, not sure. This food thing has me completely lost too & is a whole different matter.