Even though your puppy may look all grown up, the stages of his or her development last for a year or two before being considered an adult dog. The greatest puppy development changes happen from birth to 12 weeks of age, but even after that, your fur-kid still has a lot of growing up to do.
How Puppies Develop
The juvenile puppy period generally begins at age 10 weeks and lasts until puberty and the onset of sexual maturity.
It's during this period that puppies begin to learn the consequences of behavior and begin to determine what's most appropriate to certain circumstances. Puppies at this age have boundless curiosity, exasperating stubbornness, and enthusiastic affection. As long as you expect your pup to get into everything, you won't be disappointed. In fact, this is an ideal time to begin dog training.
Nearly every waking moment of this juvenile period is spent in play, which is great fun for babies and great practice for canine life. With play, puppies learn how to do important dog activities like chasing and running, pawing, biting, and fighting. Social skills and canine etiquette are also learned by interaction with littermates and Mom. Interestingly, puppies learn to inhibit their bite when they are bitten by another pup, and at this stage, they start to understand canine language. Through play, they also begin to practice dominant and submissive postures in preparation for life in the real world.
10 to 16 Weeks: Juvenile Delinquent Pups
Puppies test their boundaries during the 10 to 16 week period, which lasts anywhere from a few days to several weeks. These dogs challenge their owners to see who calls the shots, seem to “forget” any training they’ve already learned, and generally act like rebellious teenagers.
Some of this behavior has to do with teething, as pups lose baby teeth around three months of age. There can also be discomfort, as permanent teeth erupt and puppies tend to chew on anything and everything to relieve the pain.
Delinquent behavior may also be influenced by hormones. Unlike other species, a male puppy’s testosterone level (from age four to 10 months) may be up to five times higher than an adult dog’s. Even pups that have been spayed and neutered, prior to this stage, can develop a pushy attitude. Owners who have trained their dog right may experience difficult and frustrating phases like this and are encouraged to keep their dog on a leash and under control.
Four to Six Months
Pups grow so quickly during the four to six month period, and you may even notice changes every day. Your pup will also test and challenge you as they begin to figure out where they stand with other pets in the group. Thus, some squabbling and play fighting is to be expected. In the dog world, older animals teach pups limits, so this type of dynamic may seem scary but it's completely normal.
Similar to the earlier stage, an un-neutered male puppy's testosterone level increases at around four to five months of age.
This is how adult dogs recognize that big puppies are still babies and must be taught proper dog etiquette.
Puppies may also experience a fear phase (which can last up to a month) and there may even be more than one phase in large breed dogs. This tends to correspond with growth spurts, so owners may see some “flaky” behavior or unwarranted aggression, like becoming protective of toys or territory. Simply ensure that you don’t reward fearful behavior with more attention. Instead, learn how to talk to puppies, don't use baby talk, and ignore fear rather than reward it. As you build confidence through training, your pup should naturally transition out any fear phases.
Six to 12 Months: Adolescence
Most of your pup’s growth in height finishes by the six to 12 month period, but he or she may continue to fill out and gain muscle mass and body weight.
At this time, puppy coats start to also be replaced by the adult coat. While your baby may still be emotionally immature, you'll start to see leg-lifts and marks with urine. Girl pups may also go into heat (estrus) as early as five to six months, while boys begin to get interested in sex during this period.
Puppies seem to explode with high energy and do well with structured play and exercise during adolescence. Training and continued socialization are vital to ensure that your youngster knows how to behave politely with other dogs, additional animals like cats, and more people including children and strangers.
One and Two Years: Social Maturity
Depending on the breed, your dog will be physically mature between one and two years old. Small dogs mature much earlier, while larger ones take more time. Your pup’s social maturity also depends on his or her experience with other animals. For example, socialization and training should continue throughout your pet’s lifetime, because there are always new things to learn and old lessons to revisit and practice.