Adaptation Physiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH, The Netherlands.
Physiol Behav. 2012 Oct 10;107(3):433-9. doi: 10.1016/j.physbeh.2012.08.002. Epub 2012 Aug 19.
Fearfulness of an individual can affect its sensitivity to stress, while at the same time the social situation in which an animal lives can affect its fear level. It is however unknown what the long-term effects of high fearfulness on sensitivity to stress are, on individual or group level in laying hens. We hypothesize that increased fearfulness at a young age results in increased sensitivity to stress at an adult age, and that this relation can differ between groups, due to differences in group composition. Therefore, we studied the relation between fearfulness in an Open Field (OF) test at six weeks of age and plasma-corticosterone (CORT) levels after a 5-min Manual Restraint test (MR) at 33 weeks of age, and assessed behavior in the home pen. We used birds from a low mortality line, selected for four generations on low mortality due to feather pecking and cannibalism and a control line (n=153 in total, eight pens/line). These lines are known to differ in fearfulness and stress physiology. Chicks from the low mortality line were more active in the OF compared to chicks from the control line. Chicks that showed a fearful response (no walking, no vocalizing) in the OF test had higher CORT at 33 weeks of age than chicks that walked and/or vocalized in the OF test and had higher activity in the home pen as adults. On group level, a passive response in the OF was related to high CORT levels after MR. Presence of at least one fearful bird in a group led to higher CORT in the other group mates compared to birds from groups with no fearful birds present. Birds from groups in which more than 50% of birds had severe comb lesions had higher CORT levels compared to birds from groups with less than 50% of birds affected. High fearfulness of laying hen chicks can on individual level have a long-term effect on stress sensitivity. The presence of fearful birds in a group as well as signs of social instability in a group, indicated by comb lesions, can affect sensitivity to stress of birds from the same group. The mechanism by which this occurs can lie in social transmission of (fear related) behavior, but this suggestion needs further investigation.
个体的恐惧会影响其对压力的敏感程度，而动物所处的社会环境也会影响其恐惧水平。然而，我们并不清楚在产蛋鸡个体或群体水平上，长期的高恐惧状态对压力敏感性的长期影响是什么。我们假设，幼年时的恐惧增加会导致成年时对压力的敏感性增加，而由于群体组成的不同，这种关系在不同群体之间可能会有所不同。因此，我们研究了六周龄开放式场测试（OF）中的恐惧与三十三周龄 5 分钟手动束缚测试（MR）后的血浆皮质酮（CORT）水平之间的关系，并评估了其在产蛋箱中的行为。我们使用来自低死亡率线的鸟类，这些鸟类经过四代的选择，以降低因啄羽和同类相食导致的死亡率，以及一个对照组（总共有 153 只鸟，每组 8 只）。这两条线在恐惧和应激生理学方面已知存在差异。低死亡率组的小鸡在 OF 中比对照组的小鸡更活跃。在 OF 测试中表现出恐惧反应（不走路，不发声）的小鸡在 33 周龄时的 CORT 水平高于在 OF 测试中行走和/或发声的小鸡，并且成年时在产蛋箱中的活动水平更高。在群体水平上，OF 中的被动反应与 MR 后 CORT 水平升高有关。群体中至少有一只恐惧的鸟类会导致其他群体成员的 CORT 水平升高，而不是没有恐惧鸟类的群体。群体中超过 50%的鸟类出现严重鸡冠损伤的鸟类的 CORT 水平高于群体中少于 50%的鸟类。产蛋鸡小鸡的高恐惧程度可能会对压力敏感性产生长期影响。群体中存在恐惧的鸟类以及群体中鸡冠损伤等社会不稳定的迹象，会影响来自同一群体的鸟类对压力的敏感性。这种情况发生的机制可能在于（与恐惧相关的）行为的社会传递，但这一说法需要进一步研究。
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