Puppy Behavior: A Sensitive Period for Puppy Socialization

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How do we know when it is and whether it’s important?

By Dr.Sophia Yin DVM
R.I.P. 1966-2014

You’ve probably heard that puppies need to be socialized, but how do we know this and what do we know? Most of the ground breaking studies were done in the 1950’s and 1960’s, one of which was performed by co-authors, David Freedman, John A. King and Orville Elliot and published in Science in 1962. They carried out a classic study using the methodology that had already been established for determining critical periods in other animals such as ducks, guinea pigs, chickens, and sheep. They took 5 litters of cocker spaniels and 3 litters of beagles and raised each litter with their mom in a one-acre fenced field in isolation from humans.
Then, 29 pups were used in the socialization treatment groups and were taken and socialized for a week while 5 puppies remained as un-socialized controls. Puppies in the socialized group were socialized for a week either at 2 weeks of age, 3 weeks of age, 5 weeks of age, 7 weeks of age or 9 weeks of age and then returned to live in the field. During their week of socialization, the puppies were played with, tested and cared for during 3 daily 30-minute periods.

Behavior during the week of socialization

The age-related differences between the pups was clear, even at the start of socialization. The pups socialized starting at 5 weeks of age were significantly more attracted to humans than puppies that started socialization at 2,3 and 9 weeks of age. The low scores for the 2 and 3-week old pups was due to their immature motor skills; however, the low scores in the 9-week olds occurred because these puppies tended to avoid the handler! They were fearful! Luckily by the end of the week of socialization all except for the 2-week olds were equally attracted to the handler.

Researchers also found a difference in interactions when puppies were left in a room with a person who was lying passively. Two-week olds were too immature to interact much, but three-week olds spent most of the 10 minutes pawing at, climbing on and mouthing the person and his clothing. Five-week olds were wary at first but played by the end of the first session. The 7 and 9-week old puppies were frightened and stayed away from the passive human for the first several sessions. The 7 week-old puppies were comfortably playing with the person until day 3 but the 9 week-olds weren’t until day 4. Hence the fear response to humans (and most likely other new objects, environments, and animals) is more developed and increasingly difficult to reverse as the puppy ages. However, it was fairly easy to reverse in the puppies in this stage up to 9 weeks of age.

Sociability Tests at 14 Weeks of Age

After the week of socialization, the puppies were placed back in the one-acre field and lived without contact from humans. Then, when puppies reached 14 weeks of age, they were tested over a two-week period during which they received daily contact with humans. Three types of tests—handling test, leash test, and reactivity test—were performed. The results were again dramatic. At the 16th week (after two weeks of daily contact with humans) only the control groups scored significantly lower on the handling test. These puppies were fearful. Even after conclusion of the study when the researchers decided to take one of the control puppies and continue its socialization for 3 months, this puppy showed only minimal improvement at the handling test. In other words, puppies need good socialization experiences before 14 weeks of age.

The researchers also performed a leash-control test devised to test the dog’s ability to learn to respond to leash guidance. Dogs socialized at 5,7, and 9 weeks of age were significantly easier to train than the control puppies.

The final test was the reactivity test where each pup was fitted with a physiologic harness that held them. Heart rate was monitored using an EKG and depth of respiration, and muscle tensions were measured and scored concurrently. The pup was then exposed to a variety of stimuli one at a time. They included: cajoling vs. threats from a human, a loud, startling sound, and mild electric shock. Overall the controls were significantly more inhibited (they froze), tense, and had higher heart rates than the pups socialized at 7 weeks of age. They were easy to handle, responded well to being on leash (fewer balks, calm enough to eat), and were the least fearful of potentially scary stimuli.

The Take Home Message?

First, the puppy’s socialization should start early—before 5 weeks of age, because by five weeks the puppy is showing fear responses to people, objects and other unfamiliarity around them. That means it’s essential that breeders and foster puppy caretakers carry out a socialization plan. Secondly, the socialization should start before 14 weeks of age or many puppies will be doomed to a life of fear unless they go through a regimen of socialization that’s more intense than the 1.5 hours a day carried out by the researcher here. The message is simple and straightforward and taking it to heart can be the difference between having a happy well-adjusted dog or one fearful of people, objects, other animals, and various environments that we humans perceive as safe.

For more information and step-by step-socialization, see Perfect Puppy in 7 Days: How to Start Your Puppy Off Right. Don’t forget to download your free socialization checklist as part of our ‘Create the Perfect Puppy” resource bundle for free or a donation!

Dr. Yin Passed away in 2014 but her legacy lives on.


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11 responses to “Puppy Behavior: A Sensitive Period for Puppy Socialization

  1. Great article, and we love your Perfect Puppy book! We have a challenging issue with our newly-adopted rescue pup. She’s about 5 months old and was seized by the police from a hoarding situation. She’s very sweet and loving to us (and already has learned to “sit politely” for attention, treats, food, and to go out the door) but has a great fear of the crate (and we are following your crate-training recommendations …she’s perfect when we’re in the room but cries and whines when we leave … we do not reward that behavior by letting her out though) and worst of all, potties in the crate when she’s left alone, as I left her for 10 minute when I was in the shower this morning! So I’m wondering your advice for dealing with pups who come from less-than-ideal home situations during their formative weeks/months.

  2. And puppy classes? Can be effective?
    When a puppy, with 4 months old, with no socialization, fear responses, etc… the puppy classes work?

  3. Slightly embarrassed that I haven’t heard of this research before, just that of Scott and Fuller. Thank-you!


  4. Hi I have a ten month bull whip it and he is destroying my furniture and barking all of the time……..can you advise me please

  5. Janice:

    Read the articles on separation anxiety in this blog. Important to work on training the pup that calm behavior gets people to come back (see the section in perfect puppy that’s specifically on that under the learn to earn chapter–in that section the dog is tethered). If you’re not seeing a quick improvement, I’d invest in help from a qualified behaviorist before this develops into something serious.

  6. Hi Pedro:
    Puppy classes can be helpful in fearful dogs if they are good puppy classes where you get enough personalized attention and the instructors know how to work with fearful puppies. Otherwise they can actually make puppies worse too (see https://drsophiayin.com/blog/entry/how_puppy_class_nearly_ruined_my_dads_new_pup). If you read the articles in this blog on how to work with fearful dogs, you’ll get a good idea of what the trainers should be recommending! Good luck!


  7. HI Margaret:

    For puppies and adolescent dogs that are hyperactive and/or out of control (e.g. have no self control), we take them through the Learn to Earn program. This helps them quickly learn self control. This program is detailed in Perfect Puppy in 7 days (book). you can see how one puppy progresses through this plan on the DVD Creating the Perfect Puppy (https://drsophiayin.com/products). For detailed instruction on how to do first learn to earn exercises (say please by sitting, repeat sits backwards, leave-it), see Reactive Dog Workshop 1 DVD. good luck!

  8. Thank you for responding! Yes, we have been tethering her away from us throughout the day for short periods and she is doing much, much better in the crate. No accidents 4 days in the crate (fingers crossed) and she only whines or cries for a few moments before stopping. Her puppy nature is emerging and she’s very playful, and warms up fairly quickly to guests in the house.

    We’d now like to work on her pottying in front of the house, rather than in back (the landlord’s backyard). Our suburban street is a little noisy and she gets quite skittish and distracted on our brief walks, especially if a person comes out of their house. I’ve tried the 5-minutes outside/15 in crate and she just won’t go out front. We start puppy class with her tomorrow so maybe that will build her confidence! Thanks again.

  9. Socialization is defined as a dog’s ability to cope with their environment not so much how they act around humans. We are just a small part if the process.
    We know so much more now than when that study was conducted.
    Poor example

  10. I have a 4 month old rescue, Jack Russell-Shih Tzu female. She will only allow me to walk her, hold her, be near her, you name it. I have had her two weeks and she is terrified of my husband and grown son (both dog lovers) and guests in general to the point of shrieking and biting if they try to pick her up. With me she is totally loving and normal. I have never seen a dog do this. Advice?

  11. Our 11 week old german shepherd pup is bitting us all the time harder and harder, and then barks and it is almost sounds like little growls when she does not get her way, how do we take care of this, starting puppy classes next week, but our feet and hands need a break. help!!!!

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