Temporal differences in the responses of the pituitary adrenocortical axis, the sympathoadrenomedullar axis, heart rate, and behaviour to a daily repeated stressor in domestic pigs

In this study we examined responses of domestic pigs (Sus scrofa domestica) to a daily repeated stressor. In particular, we focused on differences in temporal changes across treatment repetition between the pituitary adrenoco rtical axis, the sympathoadrenomedullar axis, heart rate, and behaviour. To induce a stress response, we separated eight castrated male pigs from thei r group mates visually and auditorily for 1 h on 10 successive days. Overal l, enhanced plasma levels of cortisol, ACTH, and adrenaline indicated a cle ar stress response. Levels of cortisol and ACTH decreased continuously with repetition of exposures to the stressor. In contrast, levels of adrenaline , behavioural activity, and heart rate did not change consistently across r epetition of exposures. Interestingly, therefore, hormones of the pituitary adrenocortical axis showed a process of adaptation whereas subjects did no t adapt to the stressor with respect to titres of adrenaline, heart rate, a nd particular behaviours (e.g., grid pressing, vocalisation, locomotion). I nstead, they continued to react actively towards the social separation. Our results suggest that different stress systems can differ in temporal patte rn of their response towards a repeated stressor. Such temporal differences should be considered when studying the effects of repeated stress. (C) 199 9 Elsevier Science Inc.