«Doggie breath» could mean that your dog isn't feeling well: The reason for the nasty stench is usually bacteria in your pooch's mouth, which will result in the accumulation of plaque.
Unusually bad dogbreath can be a sign of a health issue or just a result of a nasty habit (e.g., poop munchers), so it's important to find out what's the reason behind the foul smell that's coming out of your pet's mouth before you treat it.