YUCKY BAD BREATH is often caused by build up of plaque. Also bacterial germs breed in mouths that are not cleaned or brushed. Just like us, they have teeth that need proper care.
In addition to plaque, sometimes food that is eaten can leave bad breath. Or if something eaten doesn't agree with our stomach can cause acid indigestion, which can produce
HORRIBLE ODOR.
Although, I must confess I have never brushed any other teeth except my own and my 2 chihuahuas. They get their teeth cleaned once per year by my vet. Daily they get their teeth brushed by me with a peanutbutter flavored toothpaste.
YUMMY!For those inbetween occasions of bad breath, I keep doggie breath mints. They also make one for cats.
Good luck brushing Boo's teeth. I'd love to hear how it goes.