Puppies are born before they're fully physically developed, so their first few weeks of life are full of significant changes and growth. Some developmental milestones can help you pinpoint the age of newborn puppies within a week or so. Puppies that have had rough starts may be developmentally delayed, however.
Observe the puppies to see how far they stray from mom: Newborn puppies spend most of their time sleeping and the rest of their time eating, so they don't stray too far from their dam for the first week or two. After that first week or two, puppies are more active and may wander farther away; the mother may leave the puppies for short periods of time as well.
Check the puppies' eyes to see if they're open. Puppies are born with their eyes closed; the eyes start to crack open at about 1 week of age and are usually fully open by 2 weeks old. The puppies still cannot see well at this age; they cannot track a ball rolling across the floor, for instance, until 4 to 5 weeks of age.
Make a sharp sound to see if the puppies respond. Like the eyes, puppies are born with their ear canals closed; the ears open between 1 week and 2 weeks of age. Again, at first hearing is nonspecific; the puppies may startle or react to the noise but will be unable to pinpoint its origin. At about 3 weeks puppies will start growling or barking at noises.
Watch how the puppies move. If they are crawling around the box, they are probably less than 3 weeks old. Wobbly walking starts at about 3 weeks, and by 4 weeks they can use their legs fairly well. Hind end awareness develops later, and even 5- or 6-week-old puppies will lose control of their back ends and take a tumble, especially while running.
If possible, check inside a puppy's mouth. Teeth begin to show at 3 weeks of age and most are through by 4 weeks. Once the needle-sharp teeth emerge, the mother will begin limiting the amount of time the puppies nurse and may start regurgitating food for her puppies.
- Newborn puppies are sensitive to light and sounds; when testing sight or hearing, use muted light and soft, though distinct, sounds.