A mother dog is pregnant with her litter for roughly 63 days after she is bred. By the time she whelps her puppies, there is no evidence that their sire retains fatherly feelings toward his new family. That doesn't mean that he can't eventually play a role in their rearing, though, especially if he's a member of the household.
Mom Needs Privacy
A mother dog's instinct toward her litter is to nurture and protect them. For the first few weeks of their lives, she will not welcome any canine interaction with her litter. She may become agitated or aggressive toward other dogs who approach the whelping box, including the sire, even if they are regular family members. The father dog may trigger her protectiveness by trying to sniff or nose the newborn puppies, so he should not be allowed to visit them yet. It's best to keep mom and her puppies in a quiet room by themselves until the puppies are at least 3 weeks old.
Once the puppies are 3 to 4 weeks old, they begin to move around and explore their surroundings. At this point, other family pets can be allowed to visit the new arrivals. By 4 weeks of age, the mother dog is beginning to wean her puppies and is usually more willing to accept the presence of other dogs. If the father dog is a household member, this is a good time to let him observe the puppies, although they are still too young for any contact.
Time to Socialize
When the puppies are 5 to 6 weeks old, they are mobile and eager for new experiences. The mother dog will begin to teach them manners and will usually allow the sire to take part. Each dog is different, but some father dogs will actively participate in the puppies' training, teaching them how to play and behave with other dogs and their littermates. The father dog can play a valuable role at this point in their early training, as long as he's gentle and not overly physical with them.
Although there is no evidence that father dogs recognize their puppies, some do exhibit behaviors that indicate they may. Before dogs were domesticated, father dogs played a more active role in the rearing of litters. Some sires still exhibit some of that instinct and seem protective of their puppies. They may even take part in cleaning the litter.