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

Abstract 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 χ 2  = 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