Understanding underlying mechanisms for feather-pecking behaviour in laying hens

产蛋母鸡的现代生产系统与许多严重的动物福利问题有关。随着全球母鸡数量达到50亿只，这些改进有可能对大量动物产生积极影响。最具挑战性的问题之一是啄羽(FP)，即个体重复啄食其他鸟类，拔出羽毛，经常导致严重的皮肤损伤。尽管经过50多年的研究和努力缓解这一重大问题，但其原因尚不完全清楚，也没有出现切实可行的解决方案。最近的一项流行病学研究表明，蛋鸡中FP的患病率为60%-80%，FP患者的死亡率高达20%-40%。这些死亡率相当于每年有数亿只鸟死于FP。通常有两种方法来理解动物的异常重复行为(ARB)：一种是行为学观点，强调环境和物种生物学在行为塑造中的作用，而功能障碍观点强调慢性应激或不适当的饲养环境可能导致的潜在功能异常。这两种方法都可能导致ARB，但它们的相对重要性和它们如何相互作用尚不清楚。到目前为止，在FP研究中，这两种方法总是被单独研究。我的长期目标是将两者结合起来：1.行为学观点认为，FP反映了在营养、身体和感官缺乏的环境中，高度动机的觅食/觅食行为不能正常执行的持续动机挫折感；和2.FP反映潜在的大脑/肠道功能障碍的功能障碍的观点，测试来自对人类行为抑制控制障碍的研究得出的假设，例如5-羟色胺(5-HT)缺乏会增加行为控制受损和胃肠道(GI)功能障碍的风险。为了解决这个问题，我的具体短期目标是：1.测试FP是否是由次优条件(非自然主义饮食)引起的，这是否导致动机挫折感(通过使用消费者需求方法测量返回最佳状态的动机来量化)和/或大脑/肠道功能障碍(通过操作学习测试/GI运动测试、病理组织学来量化)；2.测试FP是否由无母教养引起，如果是，是否导致行为控制缺陷(通过操作学习测试量化)和/或肠道功能障碍(胃肠动力测试、病理组织学)；3.确定动机挫折、行为控制缺陷和肠道功能障碍是否具有相加效应，从统计上比每个过程单独解释FP的差异更多；4.测试FP的不同方面是否由不同的潜在原因介导；具体地说，动机挫折是否更强烈地预测FP的形式和时机，而大脑/肠道功能障碍更强烈地预测FP的持久性(对环境浓缩的抵抗)；5.评估5-羟色胺是否是导致FP的脑和胃肠道功能障碍的关键分子。这项工作将首次揭示FP是否表明大脑和/或肠道功能障碍；有助于识别可能既减少FP又防止动机进食/觅食挫折的环境；并确定动机挫折和行为去抑制是否互补。总体而言，这项研究将解释FP的不同方面，是FP如何概念化的突破，并有助于提供一种全新的方法来解决其他物种的ARB问题。

Modern production systems for egg-laying hens are associated with many serious animal welfare concerns. With global hen numbers of 5 billion, improvements have the potential to positively impact a huge population of animals. One of the most challenging issues is feather pecking (FP), in which individuals peck repetitively other birds, pulling out feathers and often causing significant skin damage. Despite 50+ years of research and efforts to alleviate this major problem, its causes are not fully understood and no practicable solution has yet emerged. A recent epidemiological study showed that FP in laying hens has a prevalence of 60-80%, with mortality rates of up to 20-40% in FP victims. These mortality rates translate to hundreds of millions of bird dying due to FP each year. In general there are two approaches to understanding abnormal repetitive behaviours (ARB) in animals: one, the ethological view, emphasizes the role of the environment and biology of the species in shaping behaviour, while the dysfunctional view emphasizes possible underlying abnormal functioning induced by chronic stress or inappropriate rearing environments. Both approaches may contribute to ARB, but their relative importance and how they interact is unknown. In FP studies to date, these two approaches were always investigated in isolation. My long-term objective is to integrate both: 1. the ethological view that FP reflects sustained motivational frustration of foraging/feeding behaviour in a nutritionally, physically and sensorily deprived environment where highly motivated foraging/feeding behaviours cannot be executed normally; and 2. the dysfunctional view that FP reflects underlying brain/gut dysfunction, testing hypotheses derived from studies of behavioural inhibitory control disorders in humans such as hair pulling disorders where serotonin (5-HT) deficits increase the risk of impaired behavioural control and gastrointestinal (GI) dysfunction.To address this, my specific short-term objectives are to:1. test whether FP is induced by suboptimal conditions (unnaturalistic diets), which lead to motivational frustration (quantified by measuring motivation to return to an optimal condition using a consumer demand approach) and/or by brain/gut dysfunction (quantified by operant learning tests/GI motility tests, patho-histology);2. test whether FP is induced by motherless rearing, and if so, whether this leads to behavioural control deficits (quantified by operant learning tests) and/or gut dysfunction (GI motility tests, patho-histology);3. determine whether motivational frustration, behavioural control deficits and gut dysfunction have additive effects, statistically accounting for more of the variance in FP than each process individually;4. test whether different aspects of FP are mediated by different underlying causes; specifically, whether motivational frustration more strongly predicts FP’s form and timing, while brain/gut dysfunction more strongly predicts FP’s persistence (resistance to environmental enrichment);5. assess whether 5-HT is the crucial molecule in dysfunctions of brain and GI that help cause FP. This work will reveal for the first time whether FP indicates brain and/or gut dysfunction; help in identifying environments likely to both reduce FP and prevent motivational feeding/foraging frustration; and determine whether motivational frustration and behavioural disinhibition are complementary. Overall, this research will explain different aspects of FP, be a breakthrough in how FP is conceptualized, and help to provide a completely new approach to address ARB in other species.