![]() Sheep exposed to 6 weeks of unpredictable and uncontrollable events were shown to have increased fearfulness. However, very little is known about the influence of long-term challenges on emotional and HPA-axis responses to subsequent challenges. Long-term or repeated exposure to challenges may also have consequences for the ability to adapt to novel events or additional challenges, due to the already increased allostatic load of an individual under stress. ![]() Exposure to long-term challenges can eventually lead to mood changes and it has been hypothesised that maladaptive stress responding may increase the risk of developing depressive or anxious emotional states. Such maladaptive stress responses can reveal themselves in multiple ways, such as lack of adaptation to a challenge, a prolonged response to a challenge or an inadequately low response to a challenge. The excessive wear and tear (allostatic load) on homeostatic pathways during chronic stress may eventually lead to dysregulation of the HPA-axis. A chronic stress state is accompanied by a number of neuro-chemical changes such as hyper- or hypo-activity of the HPA-axis, down regulation of the HPA-axis and alterations to a number of receptor systems. ![]() The impact of the challenge varies depending on the predictability, controllability, ambiguity and chronicity of the challenge. A protracted redirection of biological resources away from biological activities that were occurring before the challenge is a hallmark of failure to adapt and characterizes stress. However, if the challenge is prolonged or occurs repeatedly, it can eventually result in chronic changes in the behaviour and physiology of the animal a biological state often referred to as chronic stress. Adjustments in internal body temperature also occur in response to challenges and may be a useful indicator of adaptation to the challenge. This is an adaptive response through which the individual attempts to cope with the challenge and regains energy homeostasis. In response to a challenge, the hypothalamic-pituitary-adrenal (HPA) axis is activated allowing the individual to physiologically and behaviourally respond to the challenge. Furthermore, little knowledge exists on how long-term exposure to environmental challenges modulates emotional and physiological adaptation to additional challenges. However, very little quantitative evidence is available on how repeated or continuous exposure to challenges alters the emotional state of animals, which is an important aspect of their welfare. Captive animals, such as farm, zoo and laboratory animals may experience several simultaneous challenges, such as barren housing conditions, painful husbandry procedures, rest deprivation and other stressful rearing and handling practices. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist.Įnvironmental and psycho-social challenges are encountered on a regular basis throughout an animal’s life. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: All relevant data are within the manuscript and its Supporting Information files.įunding: This work was supported by an Office of the Chief Executive Postdoctoral Fellowship Award, awarded by the Commonwealth Scientific and Industry Research Organization to CL, Australia. Received: AugAccepted: JanuPublished: January 30, 2019Ĭopyright: © 2019 Verbeek et al. ![]() PLoS ONE 14(1):Įditor: Judith Homberg, Radboud University Medical Centre, NETHERLANDS Citation: Verbeek E, Colditz I, Blache D, Lee C (2019) Chronic stress influences attentional and judgement bias and the activity of the HPA axis in sheep.
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