Although I don't agree with all in this article it is a good starting point.  Check with your vet, brush their teeth, I don't usually recommend the type of chews they show because I believe there are better.  Stop in and we can show you some.

The causes of bad breath can range from mild to severe, which is why it’s important to know what you’re dealing with.

Some of the most common causes of bad breath are:

  • Tooth decay
  • Oral infections
  • Lip infections (which happen the most in spaniels)
  • Gum disease

If you’re not brushing your dog’s teeth on a daily basis, tartar and plaque will build up over timeleading to bad breath or something more serious. The problem is that many owners don’t know that their dog has gum disease: Up to 80% of dogs have gum disease and only 20% of owners know about it.

Great article from Animal Wellness check it out here