When do collies get their second teeth?

Collies are a breed of dog, not a type of fish, so they do not get a second set of teeth. Dogs, like most mammals, have two sets of teeth: deciduous (or "baby") teeth and permanent teeth. Deciduous teeth start to erupt when puppies are about 2-3 weeks old, and they are all usually in place by the time the puppy is about 4 months old. The permanent teeth start to erupt when the puppy is about 6 months old, and they are all usually in place by the time the dog is about 2 years old.