Try brushing his teeth...giving him probiotics or live cultured yogurt with his breakfast. My dogs don't have bad breath and I feed them First Mate lamb and rice.
All dogs have bad breath but it wouldn't hurt to have his teeth checked. Get him one of those dental chew bones that you can find at any pet store.
I have heard parsley sprinkled through their food helps,could also mean time for a dental check up with the vet.
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