Very young puppies don't look much like the dogs they will one day become, and the first 12 weeks of life are a transformative time. Each pup develops a little differently, but as a general rule, smaller dogs tend to mature earlier, and some large and giant breeds don't reach physical maturity until they're 2 years old.
For most dogs, puppyhood ends between the ages of 6 and 18 months, marking the start of adolescence. Adulthood begins at 1 to 3 years, and dogs are considered seniors once they reach 6 to 10 years of age.
• Stage 1: Whelp. A whelp is any just-born carnivorous animal. The word is most often associated with newborn puppies. Whelping means birthing; to have whelped means to have given birth.
• Stage 2: Neonate. Neonate refers to a newborn pup from day 0 to day 13 of life. Neonate puppies can't see (their eyes are still closed), can't hear (their ears are sealed shut) and can't pee or poop without stimulation (licking) from mom.
They have no teeth, nor do they have the ability to regulate their own body temperature.
These tiny babies depend on mom and their littermates to stay warm, which is why they tend to snooze in furry little piles. Neonates sleep about 90 percent of the time, and when they're awake, they're nursing.
Fortunately, they're born able to smell, which helps guide them to mom's nipples at mealtime.
The first milk a mother dog produces is colostrum, which contains the antibodies that transfer maternal immunity to help protect the pups from opportunistic diseases during their first weeks of life.
Virtually all the energy a neonate's body generates goes toward growth. They typically double their birth weight during the first week of life. Since they can't yet stand, they sort of paddle around using their front legs. This soon leads to crawling.
It's during this time (days three to 16) that many proactive breeders institute early neurological stimulation ("super puppies," as some say) which can oftentimes result in more balanced adult dogs.
• Stage 3: Transition period. The transition period covers days 13 through 21 of a puppy's life. The ears start to open at around day 14, and the eyelids between days 10 to 16. As you can imagine, these events give the pups a whole new outlook (literally) on their world.
They begin to respond to smells and tastes, and their little puppy grunts evolve to whines, yips and barks. By day 15, most pups are standing up, and within the next several days they take their first unsteady steps. At this point, they go from total reliance on mom to a bit of independence.
• Stage 4: Awareness period. The awareness period is day 21 to day 28. By 3 weeks of age, pups are using their senses of sight and hearing to learn. They're beginning to play with their littermates and explore their environment.
This is also the time during which puppies gain some control over elimination and begin moving away from their "den" (sleeping area) to pee and poop.
• Stage 5: Socialization period. The initial socialization period encompasses weeks 3 to 8 in a puppy's life. It's during this period that her interactions with other pets and people increase, and she's able to form attachments.
At about 4 weeks of age, mom's milk production begins to taper off, and the puppies' calorie requirements increase. As mom gradually weans her pups, they begin showing serious interest in solid food.
As luck (and more importantly, nature) would have it, at 3 to 4 weeks, the canine teeth begin to push through, and a full set of puppy teeth make an appearance between weeks 4 and 6.
Age 6 to 8 weeks is considered a critical time in every puppy's socialization period. This approximately two-week window is when puppies are most accepting and least fearful of others.
How quickly a pup's mental development occurs is a direct result of the environmental stimulation she receives during this period. By week 8, most puppies are fully weaned. Puppies need additional, expansive socialization from 8 weeks to 6 months of age to best acclimate to all life will throw at them as adults. At 3 to 5 months, permanent teeth begin to replace puppy teeth, and by 7 months, puppy has a full set of permanent teeth.
It's important to keep in mind that these are general aging milestones. Each dog develops on his or her own timeline based on breed or breed mix and other factors.