If you're planning on selling the puppies, the answer is clear: most states prohibit the sale of puppies less than eight weeks old, according to the Animal Legal & Historical Center at the Michigan State University. If you're thinking of giving the pups away to loving homes, it then becomes a question of what's best for the little furry ones and when they're ready to leave the nest.
Best Time For Separation
Ideally, puppies should stay with mom until they're at least two months old. This gives the pups enough time to develop physically and emotionally. According to a 2011 study published in "The Veterinary Record" journal, puppies who stay with mom for at least 60 days have a much better track record of behavior -- less fearfulness, less food and toy possessiveness, and less excessive barking -- once they reach adulthood than puppies taken away from mom when they are 30 or 40 days old.
Puppy's Physical Development
Puppies can start to eat by themselves by the time they are four weeks old, according to the Animal Services Department of the City of Austin. At this age, they would be able to eat only canned dog food, not dry kibble, and preferably mixed with water to make it softer, as many young puppies will lick, rather than try to chew. Unless you're ready to bottle-feed the puppies every few hours, just as you would any non-furry baby, puppies younger than four weeks always should stay with mom. Pups should be able to start eating dry food by the age of six or seven weeks.
In some cases, early separation could be a positive thing. An example is the case of stray dogs. Between weeks four and seven, puppies enter what's called "the overlap stage," which basically is the socialization stage, where they learn cues from other dogs around them about the world, including humans. A stray mom who's afraid of humans will teach her puppies to be afraid of them too. Taking the pups away at that time might be the only way to tame them so they become adoptable. Unfortunately, pups taken away from mom at a young age tend to become more nervous dogs than those who remain with mom. However, if you're trying to rescue puppies and find them a good home, sometimes it's just a questions of choosing the lesser evil -- in this case, taking the puppies at this age might prove your only chance to adopt them out.
Risks of Early Separation
Aside from the psychological problems of early separation, there also are developmental ones. According to the American Kennel Club, the weaning period -- when you take puppies away from mom -- is a time where puppies are very vulnerable to diseases and health issues. This is because they no longer have access to mom's milk, which is designed especially to provide all necessary nutrition and to strengthen the immune system. If you take the pups away when they're too young, there's a risk they won't get enough of these antibodies.