I have a 6 month old Labrador and she has never barked!
She can be quite vocal and makes whining noises and other funny noises when trying to get attention, but if another dog barks she never barks back and I can honestly say I've never heard her.
She had a check at the vets last week, she's healthy and thriving, but the vet didn't really answer when I asked him about the barking.
Any ideas?