Physiological stress coping and anxiety in greyhounds displaying inter-dog aggression

Aggression is a relatively common behavioural problem in dogs that has both animal welfare and human safety considerations. Understanding the behavioural and physiological processes contributing to aggression is required for a better understanding of this issue. Previous studies have examined levels of anxiety and stress in the presence of aggression eliciting stimuli, however we aimed to measure stress and anxiety in a context unrelated to aggressive behaviour. We recorded the behaviour of greyhound dogs in an open field and noise stimulus paradigm as a measure of anxiety. During a routine blood donation procedure in the dogs, physiological measures of heart rate variability and cortisol release associated with stress coping were recorded. Finally, dogs were then subject to an aggression test where their reaction to an unfamiliar dog was recorded. Greyhounds that displayed aggression to the unfamiliar dog had a significantly greater increase in salivary cortisol in response to the bleeding procedure (0.97 ng/ml, 95% CI 0.11-1.83, P = 0.029). Heart rate measures also differed, with aggressive dogs having an elevated initial heart rate (18.0 bpm, 95% CI 8.4-27.7, P < 0.001) and reduced heart rate variability in the low (−1088.7 ms2, 95% CI −2114.4 to −63.1, P = 0.038) and very low (−7625.5 ms2, 95% CI −12193.0 to −3058.0, P = 0.002) frequency spectra. No difference in anxiety-related behaviour in the open field and noise stimulus test was detected between groups. These findings demonstrate that measurable differences in physiological stress coping during bleeding exist between greyhound dogs that pass or fail an aggression test in a separate context with an unfamiliar dog.