Puppy development and socialization:

The Primary and most important time for puppy socialization is the first three months of life. During this time puppies should be exposed to as many new people, animals, stimuli and environments as can be achieved safely and without causing over- stimulation manifested as excessive fear, withdrawal or avoidance behavior. For this reason, the American Veterinary Society of Animal Behavior believes that it should be the standard of care for puppies to receive such socialization before they are fully vaccinated.

Because the first three months are the period when sociability outweighs fear, this is the primary window of opportunity for puppies to adapt to new people, animals, and experiences. Incomplete or improper socialization during this important time can increase the risk of behavioral problems later in life including fear, avoidance, and/or aggression. Behavioral problems are the greatest threat to the owner-dog bond. In fact, behavioral problems are the number one cause of relinquishment to shelters. Behavioral issues, not infectious diseases, are the number one cause of death for dogs under three years of age.
Experience and epidemiologic data support the relative safety and lack of transmission of disease in these puppy socialization classes over the past 10 years in many parts of the United States. In fact; the risk of a dog dying because of infection with distemper or parvo virus disease is far less than the much higher risk of a dog dying (euthanasia) because of a behavior problem. Many veterinarians are now offering new puppy owners, puppy socialization classes in their hospitals or nearby training facilities with assistance of trainers and behaviorists. This emphasizes the importance of early socialization and training as important parts of a wellness plan for every puppy. We need to recognize that this special sensitive period for learning is the best opportunity we have to influence behavior for dogs and the most important and longest lasting part of a total wellness plan.
Outcome: Socialization is one method of preventing behavior problems in dogs; however, some oppose socialization before 16 wk of age due to the risk of contracting infectious diseases. The objectives of this study were to determine if puppies that attended puppy socialization classes and were vaccinated by a veterinarian at least once were at an increased risk of confirmed canine parvovirus (CPV) infection compared with puppies that did not attend classes..

Impact of the study: Results indicated that vaccinated puppies attending socialization classes were at no greater risk of CPV infection than vaccinated puppies that did not attend those classes.
While not a perfect analogy, a puppy’s openness to learning socials skills is similar to the way young children learn new languages effortlessly. Studies have shown that children younger than seven years old easily pick up new languages because their brains are wired to readily incorporate the words, grammar and structure of multiple languages. Like the puppy socialization period that ends at 12 weeks, this window closes for children around seven years old, after which language acquisition becomes far more difficult. You can place a 6-year old child in a Mandarin immersion class for a year and she will come out fluent in the language but if I were to attend the same class, I would likely still be struggling with the basics.
Given the fact that behavior problems are the No. 1 cause of relinquishment to shelters,4 along with the fact that 56% of dogs that enter shelters in the United States are euthanized, and that puppy classes help prevent behavior problems and increase the likelihood of retention in the home, there must be evidence of phenomenal risk of infectious disease transmission associated with early socialization classes to warrant holding puppies back. And there is no such evidence to date. In fact, renowned behaviorist Dr. R. K. Anderson, a longtime advocate for early socialization, has more than a decade of experience and data supporting the relative safety and lack of disease transmission in puppy socialization classes in many parts of the United States.

It’s unfortunate that the behavioral gains from puppy class are under such tight age constraints. The most sound advice we [veterinarians] can give clients is to acknowledge the small risk of infectious disease transmission and recommend well-run puppy socialization classes on the grounds that the relative risk is so low. Puppies, owners, and society stand to benefit enormously at the cost of a relatively small risk of exposure to a treatable infection.
Our current vaccines are excellent at stimulating immunity in older puppies in just one or two shots. However, puppies who nursed on their mother’s milk have maternal antibodies in their blood that block the immune system from responding to these vaccines. These circulating maternal antibodies protect them from bacterial and viral assault while the puppy’s immune system is maturing. But they also prevent the puppy’s immune system from becoming activated by vaccines.
Not many dog owners are aware of the fact that dogs undergo fear periods during their developmental stages. During these distinct periods dogs may gradually become more and more fearful of situations they once appeared to be accepting of. The fear may be manifested by overly cautious behaviors, where the puppy or dog approaches people or items tentatively or defensive behaviors involving barking/lunging/growling.
Dog tolerance levels are flexible and are determined by environmental factors (handler influence, training and socializing efforts) as much as they are determined by genetics. Dog Social dogs can become less social as they come into their maturity, and Dog Aggressive dogs can become much more tolerant with good direction and proper socialization. In our experience, with the combined factors of maturity, socialization, good leadership and training, most pit bull type dogs with true ‘terrier’ personalities fall comfortably in the middle spectrum of this bell curve.