At around six months of age your puppy will be turning from a juvenile into an adolescent. This can bring about changes in body shape as growth slows down and the body starts to fill out. Long legged gangly puppies will adopt more elegant adult proportions over the next six months.
Bad Behavior
This is also the time that male puppies start to think about the opposite sex, albeit in a somewhat confused way. For some dogs, cushions, furnishings and even their owner's legs can provide an outlet for their frustrations and mounting behavior is common at this age. While annoying and embarrassing, this behavior will normally settle down again after a couple of months but some dogs will continue to mount objects after this time. Neutering your male dog is a good solution in the vast majority of cases. This routine operation involves removal of the testicles - the main source of the hormones that cause these behaviors.
Changing Habits
The other change you might notice as your male dog grows up is that he will start lifting his leg to urinate. This is quite normal but a small number of dogs may also start to mark their territory by lifting their leg and urinating on objects in the home. Aggression towards other male dogs may also occur during these 'teenage' years. Again, the vast majority of these types of problems are solved by neutering and many owners choose to have their male dogs neutered at around six months before any of these potential behaviors can be demonstrated.