Puppies go through many changes throughout their puppyhood and well into adulthood. These include replacing their soft, fuzzy puppy coats with more permanent adult coats. When this change occurs varies depending on breed, size, health condition and specific growth rates of the individual pup.
Born with a Thin Coat
When a puppy is born, he already has a thin layer of fur. This peach fuzz helps keep him warm and acts as mild protection against the elements. Over the next several months, his baby fur becomes thicker and more pronounced. It continues this trend throughout puppyhood; however, a pup's coat is generally shorter than what he'll have when he grows up. Depending on breed, you may begin to notice color or pattern changes as adult fur comes in.
The Shaggy Look
Breed variations exist, but generally adult fur begins to come in when a puppy is anywhere from 3 to 6 months old. At this point, he begins to shed his old coat. Adult fur takes longer to grow than puppy fur takes to fall out, so a pup may take on a patchy, shaggy look for a while as things balance out. Gentle grooming can help keep the shedding under control, although aggressive brushing can irritate the exposed skin.
Some breeds change color or pattern as they grow. For example, Dalmations are born white as snow, only developing spots as their adult fur comes in. Other breeds are born one color, then develop an adult coat that's slightly different. Also, in some breeds with hair rather than fur -- including the poodle, Yorkshire terrier, Maltese and others -- mats can develop as puppy fur is shed. These breeds require more monitoring and clipping to avoid the development of painful tangles.
General Time Frames
Although the general age frame is 3 to 6 months of age, it can take up to a year before a full transformation is made. A puppy's body needs time to shed his old coat and grow an entirely new one, all while keeping up with other demands of growing up. The change will become obvious when you start finding clumps of fur around the house and your puppy starts to look like half his hair is missing.