The onset of adult hazard avoidance behavior (fear motor patterns) occurs during the critical period of development in domesticated canines. In wolves, the onset of adult hazard avoidance behavior occurs at approximately 19 days (Coppinger and Coppinger, 2001). This onset is delayed in domestic dogs, taking place as late as day 72 in the Labrador Retriever (Coppinger and Coppinger, 2001). The objectives of this study were to identify, compare, and contrast the onset and expression of adult hazard avoidance behavior across three breeds of puppies between four and ten weeks of age and examine developmental breed differences in heart rate, behavior, and salivary cortisol concentrations. Ninety-eight puppies were tested within three purebred breeds: Cavalier King Charles Spaniels (n=33), Yorkshire Terriers (n=32), and German Shepherd Dogs (n=33). Data were collected weekly beginning when the puppies were 4-5 weeks of age and continuing until the treatment group puppies demonstrated hazard avoidance behavior, reached ten weeks of age, or left the breeder home. Puppies took part in four tests each visit: a Novel Item Test, Teeter-Totter Test, Step Test, and Loud Noise Test. During each test, the presence or absence of crouching and hazard avoidance behavior were noted. Heart rate was measured initially, following each test, and at the conclusion of the testing period. Saliva samples were also collected to measure salivary cortisol in the puppies prior to testing and 20 minutes following the final test.
Our results indicated a significantly (P < 0.05) later onset of hazard avoidance behavior in Cavalier King Charles Spaniels compared to both German Shepherd and Yorkshire Terrier puppies. The proportion of treatment puppies exhibiting hazard avoidance behavior at any point was also significantly (P < 0.01) different: Yorkshire Terriers (82%), Cavalier King Charles Spaniel (53%), and German Shepherds (26%). Yorkshire Terriers demonstrated the highest (P < 0.05) heart rates at five weeks of age, while Cavalier King Charles Spaniel heart rates were the lowest (P < 0.03) from six through eight weeks of age.
Significant (P < 0.05) breed differences in puppy mobility were found beginning at six weeks of age, with German Shepherds demonstrating the most mobility and Cavalier King Charles Spaniels the least. There were also significant breed (P < 0.01) differences in the crouch response to the Loud Noise Test, regardless of age, with Cavalier King Charles Spaniels demonstrating the highest incidence of crouching followed by the Yorkshire Terriers. Among treatment puppies of all breeds, the incidence of crouch was significantly (P < 0.01) greater from four to six weeks of age than seven through nine weeks of age, regardless of breed or gender.
Puppies that exhibited hazard avoidance behavior also demonstrated a tendency (P < .07) of higher concentrations of cortisol from the post-test salivary collection compared to the pre-test collection. No other puppies (treatment puppies not demonstrating hazard avoidance behavior and control puppies) showed this tendency. The results of this study support the hypothesis that behavioral development and the onset of hazard avoidance behavior vary across breeds of domestic dogs.