Breed-dependent differences in the onset of fear-related avoidance behavior in puppies

The onset of fear-related avoidance behavior occurs during and, to some extent, defines the sensitive period of development in the domestic dog. The objectives of this study were to identify the onset of fear-related avoidance behavior and examine breed differences in this behavioral development. A total of 98 purebred puppies representing 3 breeds were tested, namely Cavalier King Charles spaniels (n = 33), Yorkshire terriers (n = 32), and German shepherd dogs (n = 33). Data were collected weekly beginning 4-5 weeks after birth until 10 weeks of age. Puppies took part in 4 tests during each visit: a novel item, seesaw, step, and loud noise test. During each test, the presence or absence of fear-related avoidance behavior and crouched posture were noted. Saliva was also collected to measure salivary cortisol concentrations in the puppies before and after testing. A later onset of fear-related avoidance behavior was observed in Cavalier King Charles spaniels compared with German shepherd dog and Yorkshire terrier puppies (F = 11.78, N = 29, P < 0.001). The proportion of treatment puppies that exhibited fear in response to the testing was also different (χ2 = 9.81, N = 56, P = 0.007): Yorkshire terriers (N = 14, 78%), Cavalier King Charles spaniel (N = 10, 53%), and German shepherd dogs (N = 5, 26%). Cortisol concentrations decreased with age. Cavalier King Charles spaniel puppies that demonstrated fear-related avoidance behavior exhibited a greater (t = 2.133, N = 79, P = 0.036) cortisol response than puppies that did not exhibit the behavior. Breed differences in the crouch response to the loud noise test, regardless of age, were observed (F = 18.26, N = 98, P < 0.001). Cavalier King Charles spaniels demonstrated the highest incidence of crouching followed by the Yorkshire Terriers. Breed differences in puppy mobility were observed beginning at 6 weeks of age, with German shepherd dogs demonstrating the most mobility and Cavalier King Charles spaniels the least. The results of this study support the hypothesis that emotional and behavioral development, as well as the onset of fear-related avoidance behavior, varies among breeds of domestic dogs.