The early weeks of puppy development are crucial. During this delicate time, the dog learns how to navigate his environment and how to interact with other dogs and animals. Introducing a puppy to his father is an important step in the socialization process that helps him learn correct behaviors and keeps him on the path toward being friendly with other dogs.
For the first few weeks after birth, a mother dog will be especially protective of her litter. Introducing the father at this time could result in a tussle between him and the mother, so it is best to keep them separated until her hormones cool down. After a few weeks the mother will be more receptive to her puppies exploring the world and to other dogs coming in for a visit.
Puppies are effectively helpless for the first few weeks of life. They are born with their eyes shut and cannot walk. It is not advisable to attempt any introductions during these delicate phases, as any wrong move or accidental slip could result in a devastating injury to the puppy. The earliest a dog enters the socialization phase is age 3 weeks -- this is a bare minimum for adding new dogs to the mix.
Health and Safety
One of the biggest concerns related to introducing new puppies to their father, or any other dog for that matter, is health. Puppies are not born with immunity to disease and require the same set of vaccinations as any other dog. It is ill-advised to bring any new dog into the puppy’s area until all of the puppies have been properly vaccinated and checked for health problems.
Every dog is different, but some general rules you can follow for introducing your puppies to their father. Any time after age 3 weeks is considered the socialization period, and since puppies need their first round of shots at around 6 weeks of age, it is safe to introduce the father to the mix any time after that and before the core socialization phase closes at 13 weeks. Different breeds have different timelines, but all follow the same general course.