A newborn puppy doesn't look much like a dog and goes through different stages of puppy development during his first twelve weeks. Dogs are considered puppies from birth to one year of age and go through several puppy stages and development periods. However, each dog develops differently, with smaller dogs tending to mature earlier and some large breeds not physically mature before they are two years old.
Newborn puppies vary in size depending on the breed; tiny dogs like the Chihuahua produce puppies sized about four inches long, while giant breed newborns like Great Dane puppies may be twice that size.
Rate of puppy development also varies from breed to breed. For instance, Cocker Spaniel puppies open their eyes sooner than Fox Terrier puppies, and Basenji puppies develop teeth earlier than Shetland Sheepdog puppies. However, no matter the breed, all puppies are born totally dependent on the momma dog, technically called the bitch.
At birth, puppies are blind, deaf and toothless, unable to regulate body temperature, or even urinate or defecate on their own. Puppies depend on their mother and littermates for warmth, huddling in cozy piles to conserve body temperature. A puppy separated from this warm furry nest can quickly die from hypothermia—low body temperature. Cold, lonely puppies cry loudly to alert Mom to their predicament.
Puppies first experience the sensation of being petted when washed by their mother's stroking tongue. The bitch licks her babies all over to keep them and the nest clean, and also to stimulate them to defecate and urinate.
Neonatal Period: Birth to Two Weeks
From birth, puppies are able to use their sense of smell and touch, which helps them root about the nest to find their mother's scent-marked breasts. The first milk the mother produces, called colostrum, is rich in antibodies that provide passive immunity and help protect the babies from disease during these early weeks of life.
For the first two weeks of life, puppies sleep nearly 90 percent of the time, spending their awake time nursing. All their energy is funneled into growing, and birth weight doubles the first week. Newborns aren't able to support their weight, and crawl about with paddling motions of their front legs. The limited locomotion provides the exercise that develops muscles and coordination, and soon the puppies are crawling over and around each other and their mother.
Transitional Period: Week Two-to-Four
The second week of life brings great changes for the puppy. Ears and eyes sealed since birth begin to open during this period, ears at about two weeks and eyelids between ten to 16 days. This gives the furry babies a new sense of their world. They learn what their mother and other dogs look and sound like, and begin to expand their own vocabulary from grunts and mews to yelps, whines and barks. Puppies generally stand by day 15 and take their first wobbly walk by day 21.
By age three weeks, puppy development advances from the neonatal period to the transitional period. This is a time of rapid physical and sensory development, during which the puppies go from total dependence on Mom to a bit of independence. They begin to play with their littermates, learn about their environment and canine society, and begin sampling food from Mom's bowl. Puppy teeth begin to erupt until all the baby teeth are in by about five to six weeks of age. Puppies can control their need to potty by this age, and begin moving away from sleeping quarters to eliminate.
Socialization Period: Week Four-to-Twelve
Following the transitional phase, puppies enter the socialization period at the end of the third week of life; it lasts until about week ten. It is during this socialization period that interaction with others increases, and puppies form attachments they will remember the rest of their life. The most critical period--age six to eight weeks--is when puppies most easily learn to accept others as a part of their family. Refer to the article on how to socialize puppies.
Beginning at four weeks of age, the bitch's milk production begins to slow down just as the puppies' energy needs increase. As the mother dog slowly weans her babies from nursing, they begin sampling solid food in earnest.
The environmental stimulation impacts your puppy's rate of mental development during this time. The puppy brain waves look that of an adult dog by about the 50th day, but he's not yet programmed--that's your job, and the job of his mom and siblings. Weaning typically is complete by week eight.
Puppies often go through a "fear period" during this time. Instead of meeting new or familiar people and objects with curiosity, they react with fearfulness. Anything that frightens them at this age may have a lasting impact so take care that the baby isn't overstimulated with too many changes or challenges at one time. That doesn't mean your pup will grow up to be a scaredy-cat; it's simply a normal part of development where pups learn to be more cautious. Careful socialization during this period helps counter fear reactions.
Puppies may be placed in new homes once they are eating well on their own. However, they will be better adjusted and make better pets by staying and interacting with littermates and the Mom-dog until they are at least eight weeks old--older generally is better. Interacting with siblings and Mom help teach bite inhibition, how to understand and react to normal canine communication, and their place in doggy society. Puppies tend to make transitions from one environment to another more easily at this age, too.
Your puppy still has lots of growing to do. He won't be considered an adult until he goes through several more developmental periods and reaches one to two years of age.