A puppy’s coat will eventually be replaced by an adult coat. Since every breed is different, this may occur at different times. For most dog breeds, however, the puppy coat is replaced by the adult coat between the ages of three and six months. When the puppy’s coat is replaced, the puppy’s hair will look shaggy for a bit and might begin to fall out before being replaced by the adult fur. If you notice this happening with your puppy or notice some patchy spots for a while, it is not a reason to be concerned.