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Puppy Socialization and the Sensitive Period: When is it, and is it important?

Posted December 18, 2014 in Dog Behavior

Dr. Sophia Yin discusses the fundamental reasons for socializing puppies. For more from Dr. Yin, find her on Facebook or at

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, chicken and sheep. They took five litters of cocker spaniels and three litters of beagles and raised each litter with their mothers 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 five 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 three daily 30-minute periods.

Behavior During the Week of Socialization

The age-related differences between 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 were 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 two-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 3-week-olds spent most of the 10-minute 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. 7-and 9-week-old puppies were frightened and stayed away from the passive human for the first several sessions. The

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Sophia had several years of experience as a veterinarian, applied animal behaviorist and author. She was also a founding member of IDEXX’s Pet Health Network team.