Rapid shaping of behaviour associated with high urinary cortisol in domestic dogs

Abstract

The occurrence of stress has widely been associated with impairments in learning abilities in animals, although the influence of stress appears to differ with the complexity of tasks. Previous research has suggested that some domestic dogs exhibit both physiological (elevated cortisol) and behavioural signs of stress when newly admitted to re-homing centres. In this study we have investigated whether levels of stress as measured by urinary cortisol: creatinine is sufficient to impair the learning of simple associations. On the day following their admission to a re-homing centre, 32 dogs were trained on one classical conditioning task and one operant conditioning task; 6 days later, they were trained on a second operant conditioning task. Their mean urinary cortisol:creatinine ratio (C/C) fell from 27.1 × 10 −6 to 22.3 × 10 −6 (nmol/l:nmol/l) between these 2 days; a substantial proportion (78% on day 1, 63% on day 7) of dogs had ratios above the range of 5–20 × 10 −6, which is that defined as clinically normal ( Bush, 1991), suggesting high levels of stress. The dogs’ average time to reach criterion on either task on day 1 was unrelated to C/C or to behavioural signs of stress; this lack of correspondence may reflect the diverse previous experiences of the dogs. On day 7, the six dogs which failed to reach criterion for the operant association were significantly less active and interactive in their kennels than the others. For the remainder, a high rate of learning the operant association was associated with high C/C (in excess of 40 × 10 −6), and a poor performance was associated with fearful behaviour in the kennel. Dogs appear to have adopted one of two coping strategies: either the display of fearful behaviours and an impaired ability to learn the tasks, which may reflect a ‘reactive’ style of responding, or a higher level of HPA axis activation and an enhanced ability to rapidly learn a new task, which may be indicative of a more ‘proactive’ coping style.