Plasma cortisol variations in dairy cows after some usual or unusual manipulations

The increase of blood cortisol is a common consequence of the acute stress; this has generally positive effects, despite not completely understood (Sapolsky et al. 2000). However, at least in human beings under chronic stress, the hypothalamic-pituitary-adrenal system – responsible of cortisol release – is deregulated, resulting in pathophysiological changes, which may develop into various types of disorders (Tafet and Bernardini, 2003). According to this, blood cortisol levels could help to diagnose chronic stress; nevertheless it is not so easy because our understanding of long-term stress is poor (Ladewig, 2000). In fact, animals might adapt to long- acting housing conditions that are presumed to be stressful or might not respond with permanent alterations on the various response systems (von Borell, 2001). This could explain the fact that, according to Broom (1988), an hyper-reactivity to adrenocorticotrophic hormone (ACTH) challenge was considered index of chronic stress, while Weiss et al. (2004) consider it true in pigs but not in cattle. An explanation to these contradictory results could be also related to the management and sampling tech- niques during the challenge trials and that could induce a blood cortisol raise. This have suggested few researches to better clarify which kind of interference can be due to handling and bleeding techniques as well as to more or less common man/cow interactions.