Relating Adult Hippocampal Neurogenesis to Tonic Immobility and Longitudinal Ranging Behaviour in Commercial Laying Hens

Access to
outdoor areas is provided as a means of enhancing welfare in commercial systems
for laying hens, but proportions of time spent on the range by individual birds
vary substantially. Adult hippocampal neurogenesis in mammals and birds is
upregulated by positive experiences including environmental enrichment and
exercise, while basal levels of proliferation have been associated with
individual differences in reactive versus proactive coping style. We thus
sought to explore whether individual differences in use of outdoor areas and in
tonic immobility (TI) responses (indicative of fearfulness) were associated
with hippocampal cell proliferation and neuronal differentiation. Radio
frequency identification technology was used to track the ranging behaviour of
440 individual focal hens within a commercially relevant system over a 72-day
period, after which tonic immobility durations were measured. Following hippocampal
tissue collection from 58 focal hens, proliferation and neuronal
differentiation were measured through quantitative PCR for proliferating cell
nuclear antigen (PCNA) and
doublecortin (DCX) mRNA respectively.
Variation in ranging was not related to TI responses. Greater time spent in
outdoor areas (the grassy range and stone yard) was associated with higher PCNA expression in the rostral subregion,
while individual differences in TI duration positively correlated with
proliferation over the whole HF. Basal proliferation in the chicken HF may thus
be an indicator of reactivity, while levels in the rostral region may be
stimulated by ranging experience. DCX
expression in the caudal HF negatively co-varied with time on the range, but
was not associated with TI duration. This suggests that ranging outside may also
be associated with stress. Within laying hen flocks, individual differences in
hippocampal plasticity thus relate independently to coping style and use of external
areas.Experimental use of the animals was approved by the Bern Kantonal
Authority (BE-46/16) and the Animal Welfare and Ethical Review Body at
Newcastle University (Project ID #549), and procedures complied with Swiss
regulations regarding their treatment. Standard commercial protocols were
followed, including ad libitum access to food and water.

户外区域的开放作为提升商业化饲养鸡福利的手段之一，然而，个体鸡在户外活动区域所花费的时间比例却存在显著差异。在哺乳动物和鸟类中，成年海马体的神经发生受到积极体验的增强，包括环境丰富化和运动，而基础水平的增殖则与个体在应对策略上的反应性或主动性差异相关。因此，本研究旨在探讨个体在户外区域使用频率和静态不动性（TI）反应（恐惧的标志）的差异是否与海马体细胞增殖和神经元分化相关。利用射频识别技术，对440只个体鸡在72天商业化饲养系统中的活动范围进行追踪，随后测量了静态不动性的持续时间。在从58只个体鸡收集海马体组织后，通过定量PCR技术分别测量了增殖细胞核抗原（PCNA）和双皮质素（DCX）mRNA的增殖和神经元分化。活动范围的差异与TI反应无关。在户外区域（草地活动区和石质庭院）度过更多时间与海马体前区PCNA表达量的增加相关，而TI持续时间在个体间的差异与整个海马体区域的增殖呈正相关。因此，鸡海马体的基础增殖可能作为反应性的指标，而前区的水平可能受到活动经验的刺激。DCX在海马体尾区的表达与在活动区域度过的时间负相关，但与TI持续时间无关。这表明户外活动也可能与压力相关。因此，在产蛋鸡群中，海马体可塑性在应对风格和外部区域使用上的个体差异与独立相关。动物实验的使用得到了伯尔尼州当局（BE-46/16）和新卡斯尔大学的动物福利与伦理审查委员会（项目ID #549）的批准，且实验程序符合瑞士关于动物待遇的规定。遵循了标准的商业协议，包括自由取食和饮水。