Using high-definition oscillormetry as an indicator of chronic stress in domestic chickens

Stress causes activation of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system as part of the adaptive allostatic response. Chronic activation of the autonomic nervous system however, can be maladaptive resulting in the sympathetic nervous system repeatedly overriding the parasympathetic nervous system. This can lead to cardiovascular dysfunction, symptoms of which can include tachycardia and hypertension. The development of a non-invasive technique for determining cardiac function may therefore provide a proxy measure of chronic stress. High-definition oscillometry (HDO) has been developed for measuring cardiac activity in animals during anaesthesia, but has not yet been used extensively on birds or for detecting long-term differences in cardiac activity. We housed 14 domestic chickens (Gallus gallus domesticus) in a non-preferred environment (N), and 15 chickens in a preferred environment (P) (as determined by prior experiments), for 24 weeks. At the end of the 24-week period, all birds underwent a series of physiological and behavioural tests. A specifically designed cuff was applied to the leg of each bird and HDO was used successfully to record pulse rate, systolic, diastolic and mean arterial blood pressure. Each measurement was repeated five times for each chicken. All measures of cardiac activity were significantly positively correlated (Pearson’s correlation coefficient: all > 0.66, p < 0.001). Independent samples t-tests revealed no significant differences in systolic, diastolic or mean arterial blood pressure between the N and P birds (all p > 0.05). The pulse rate however, was significantly higher in N birds (mean: 335.6 ± 9.5 bpm) than in P birds (mean: 308.2 ± 6.1 bpm) (t27 = 2.46, p = 0.021). These results suggest that pulse rate might be more sensitive for detecting stress-related differences in cardiac function, than other measures of blood pressure in birds. Additionally, Spearman rank-order correlation coefficients were used to analyse the relationship between the cardiac function and other measurements taken within each treatment group. We found that P and N birds that were more cardiovascularly responsive in the blood pressure test reacted differently to tasks regarding punishment and reward respectively