Lady could jump out of that pen anytime she wants, but she likes playing with her kids! Watch as the puppies are enthralled watching their mom play fetch.
In general, you shouldn’t discourage puppies from play fighting. It’s a completely normal and desirable behavior in young dogs up to several months of age. Puppies brawl with their littermates, mother and friendly adult dogs to develop their skills, bodily coordination and strength control. When the puppy bites too hard, the other participant may yelp and stop playing momentarily. The lapse in play is undesirable to the biting puppy, who learns not to repeat this behavior if he wants to continue to have fun in the future. Not all puppies learn this concept quickly, though.
The occasional yelp or squeak during a play fight is standard, but pay attention to your puppies’ interactions if you start hearing a lot of “pain sounds” from the play area. It’s easy for the biggest of the litter to accidentally hurt the runts, and a nip on the ear is enough to send any puppy crying to the corner. Your puppy’s behavior is problematic if he pursues his littermates and continues to bite or brawl after they vocalize their pain, flip over in surrender or flee from him. Don’t let your pup consistently bully his brothers and sisters.
When your puppy bites you or another puppy too hard, put him in a large box or shut him away in isolation for a minute or two. This associates excessively rough play with an undesirable outcome, which helps him develop better habits. Allow your pups to play fight until they are about 4 months old. If they are still treating each other roughly, try to redirect their aggression by offering them toys when they start to bite at each other. Never use your hands when playing with your dog. Instead, hold a rope toy by one end and allow him to tug on the other.
Take a look the video in the following