Different Dog Breeds, Different Sensitive Period?

A study of three breeds finds differences in the sensitive period, and shows socialization should begin before you even take your puppy home.

The sensitive period for socialization of puppies may end at different times for different breeds, ending later in Cavalier King Charles Spaniels like this one
Photo: JL Snader/Shutterstock.com

By Zazie Todd, PhD

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Puppies have a sensitive period between 3 and 12-14 weeks old in which they must be socialized. This means positive introductions to new people, dogs, places, etc. If not, they will be fearful as adult dogs. A fascinating new study by Mary Morrow (Ohio State University) et al investigates whether this period is the same for three breeds of dog: Cavalier King Charles Spaniels, Yorkshire Terriers, and German Shepherd Dogs. 

These breeds make a particularly interesting comparison. The Cavalier King Charles Spaniel and Yorkshire Terrier are both members of the Toy group, although Yorkshire Terriers are still “terriers by nature” according to the breed standard. The German Shepherd is a Herding dog, and the GSD puppies were chosen from breeders with international working dog lines.

The results show that Yorkshire Terriers and German Shepherd Dogs have an earlier onset to the sensitive period. This means socialization needs to start in the home of the breeder (or the foster for rescue pups). People are increasingly aware of the importance of socializing puppies when they get them. But before committing to a new pup they should ask the breeder: “What are you doing to begin socialization before I take the puppy home?” 

Dr. Joy Pate (Penn State University), one of the authors, says “Socialization is clearly important for all breeds of dog. What our study shows, is that timing of exposure to novelty is not only important, but varies by breed. In breeds with earlier onset of adult patterns of fear-related avoidance behavior (the GSDs and YTs in our study), it is critical that they be exposed to novel experiences earlier than some other breeds. In the case of these two breeds, this means by about 40 days, which is before they have left the breeder.” 

“Therefore, development of a confident, emotionally competent animal depends not only on the new owner and trainer, but on the environment of the breeder. Although this is important for all breeds, for those with earlier onset of fear-related behaviors, there is a shorter window to provide necessary stimulation and exposure to novelty.”

She goes on to say, “We think that the important message here is that, while exposure to novelty and 'socialization' are necessary for development of stable adults of all breeds, the timing of this critical window is breed-dependent.

The timing of the sensitive period for socialization in puppies varies with breed
Photo: Vera Zinkova/Shutterstock

Fear-related avoidance behaviour began at 39.4 days (±1.6) for the German Shepherd, 43.6 (±2.48) for the Yorkshire Terrier, and 54.8 days (±2.74) for the Cavalier King Charles Spaniels.

One potential explanation for the results has to do with neoteny (child- or baby-like features). Of these three breeds, the CKCS is the most neotenous whereas the GSD is closer in appearance to the wolf. 

In their paper, the scientists say, “Just as dogs and domesticated foxes have longer critical socialization periods than wolves and non-selected foxes respectively, perhaps more neotenous breeds of dog such as the Cavalier King Charles Spaniel would also have a longer socialization period.” Further research with more breeds would be needed to confirm this.

Puppies were tested once a week from the age of 4-5 weeks until 10 weeks (or until they went home, if earlier). There were four behavioural tests. The control group puppies experienced the same thing but without the actual test. For example, they were placed in location for the noise test for the same amount of time as the test puppies, but did not experience the loud noise. 

Testing took place close to but out of sight and sound of the other puppies in the litter. There were four tests each week: a novel item, being placed on a seesaw, hearing a sudden loud noise, and being put on a step so they would feel like they were on a ledge. The novel item was a toy duck that walked whilst making a noise and shining light from its eyes.

In early testing the puppies did not show fear. For example, in the novel item test, a 31-day-old Yorkshire Terrier puppy stays still while the toy duck marches right up to her. At 38 days, the video shows her back away from the approaching duck and then run to hide behind the human’s legs.

The age of onset of the fear period in GSDs is similar to that found by Ray Coppinger  in earlier work. There were differences between the three breeds in the proportion of puppies that responded fearfully. From 6 weeks old, there were also differences in mobility. Most of the Cavalier King Charles Spaniels did not begin testing until 5 weeks old because they did not respond at 4 weeks. The breeders said that CKCS develop later and open their eyes later than other breeds. 

Saliva was also collected from the puppies and tested for cortisol, although only the GSDs and CKC Spaniels took part in this because of difficulties getting samples from the Yorkshire Terriers. Cortisol could be detected in the saliva from 4 weeks old. Among the Cavalier King Charles Spaniel puppies, changes in cortisol from before to after the test were greatest amongst the puppies that had a fear response.

98 puppies took part in the study (33 Cavalier King Charles Spaniels from 7 litters, 33 German Shepherd Dogs from 5 litters, and 32 Yorkshire Terriers from 9 litters). Eleven breeders participated and the puppies were tested at their homes. Among each breed, 14 puppies were controls and the remainder took part in the experimental condition. 

This study provides important confirmation that breed differences in the sensitive period exist. Although we still have much to learn about socialization, the implication is very clear – it needs to start early. Unfortunately, many puppies miss out on important socialization opportunities.

If you liked this post, check out my book Wag: The Science of Making Your Dog Happy. Modern Dog magazine calls it "The must-have guide to improving your dog's life."

Zazie Todd, PhD, is the award-winning author of Wag: The Science of Making Your Dog Happy and Purr: The Science of Making Your Cat Happy. She is the creator of the popular blog, Companion Animal Psychology, writes The Pawsitive Post premium newsletter, and also has a column at Psychology Today. Todd lives in Maple Ridge, BC, with her husband, one dog, and two cats. 

Useful links:
Morrow, M., Ottobre, J., Ottobre, A., Neville, P., St-Pierre, N., Dreschel, N., & Pate, J. (2015). Breed-dependent differences in the onset of fear-related avoidance behavior in puppies Journal of Veterinary Behavior: Clinical Applications and Research DOI: 10.1016/j.jveb.2015.03.002

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