Understanding underlying mechanisms for feather-pecking behaviour in laying hens

现代蛋鸡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，这些改进有可能对庞大的动物种群产生积极影响。最具挑战性的问题之一是啄羽毛（FP），在这种情况下，个体反复啄其他鸟类，拔掉羽毛，经常造成严重的皮肤损伤。尽管有50多年的研究和努力来缓解这一重大问题，但其原因尚未完全了解，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，卵磷脂在蛋鸡中的患病率为60-80%，卵磷脂受害者的死亡率高达20-40%。这些死亡率意味着每年有数亿只鸟死于FP。一般来说，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塑造行为中的作用，而功能失调观点强调可能由慢性压力或不适当的饲养环境引起的潜在功能异常。这两种方法都可能导致ARB，但它们的相对重要性以及它们如何相互作用尚不清楚。在迄今为止的计划生育研究中，这两种方法总是单独进行研究。我的长期目标是整合两者：行为学观点认为，FP反映了在营养、身体和感官被剥夺的环境中，高度动机的觅食/摄食行为无法正常执行的持续动机挫折；和2。功能失调的观点认为FP反映了潜在的脑/肠道功能障碍，测试了从人类行为抑制控制障碍（如拔毛障碍）的研究中得出的假设，其中血清素（5-HT）缺陷增加了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：测试FP是否由次优条件（非自然饮食）引起，导致动机挫折（通过使用消费者需求法测量返回最佳条件的动机来量化）和/或脑/肠道功能障碍（通过操作性学习测试/胃肠道运动测试，病理组织学来量化）；2. 检验生育障碍是否由无母抚养引起，如果是，是否导致行为控制缺陷（通过操作性学习测试量化）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叠加效应，在统计上解释FP的差异比每个过程单独的差异更大；4. 检验FP的不同方面是否由不同的潜在原因介导；具体来说，动机挫折是否更能预测FP的形式和时间，而脑/肠道功能障碍是否更能预测FP的持久性（对环境富集的抵抗）；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；帮助确定可能降低FP和防止动机性喂养/觅食挫折的环境；并确定动机挫折和行为去抑制是否互补。总的来说，这项研究将解释FP的不同方面，是FP概念化的一个突破，并有助于提供一个全新的方法来解决其他物种的ARB。

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.