Interactions between housing environment, chronic stress, and pathogenic infections in laying hens

鸡蛋是一种非常受欢迎的蛋白质来源，并提供许多人类饮食中必不可少的营养物质，因此鸡蛋生产的安全和可持续至关重要。此外，消费者还要求提高数百万只用于商业鸡蛋生产的母鸡的福利，这导致欧盟禁止使用电池笼，并鼓励该行业转向将母鸡饲养在无笼系统中。虽然这很受消费者的欢迎，但放养系统给母鸡带来了新的福利问题，这一点还没有完全了解。本项目旨在研究导致散养母鸡慢性应激和对致病性感染易感性增加的因素。我们的实验室最近证实了成年海马神经发生是鸟类大脑慢性应激的一种新的生物学标记。经历过长期负面福利状态的母鸡，如饲料限制（Robertson et al ., 2017）或龙骨损伤引起的慢性疼痛（Armstrong et al .，提交），在成年期海马体中产生的新神经元较少。为了比较不同饲养环境和健康条件对母鸡慢性应激水平的影响，我们将收集母鸡的大脑并对其进行免疫组织化学处理，然后对新生神经元进行计数以量化神经发生。我们预测，在压力更大的环境下生活的鸟类，海马体中新生成的细胞会比在压力较小的环境下生活的鸟类少。我们将调查的一个健康状况的例子是脚垫皮炎（FPD）。我们假设FPD引起的疼痛会导致慢性压力，并将通过比较患有严重FPD的鸟类和没有FPD的鸟类之间的神经发生来验证这一点。我们还建议使用神经发生来比较饲养在不同类型鸟舍中的母鸡所经历的慢性应激。例如，我们建议比较多层系统中饲养的母鸡与平面系统中饲养的母鸡的神经发生。我们也可以比较那些经常有掩护的鸟和那些在范围内没有掩护的鸟。众所周知，长期压力会降低免疫系统的有效性，从而增加病原体感染的可能性。这是一个进一步的福利问题，也是一个食品安全问题，因为肠道沙门氏菌等病原体的感染会危及鸡蛋的安全和可持续生产。我们将与利物浦大学合作，进一步研究慢性应激与致病性感染之间的相互作用。我们建议在蛋鸡中诱导慢性应激，这将使我们能够研究慢性应激对感染易感性和大脑的影响。在这个项目中，我们还将与CASE合作伙伴湖区自由放养鸡蛋公司合作，该公司将为我们提供150多万只母鸡，这些母鸡饲养在各种不同类型的鸟舍中。他们将协助选择住房环境进行比较，以便指导我们的项目产生与商业相关的结果。他们还将提供多年来在其农场收集的历史健康和福利数据。在实习期间，学生将对这些数据进行分析，以确定可能导致福利或产蛋量下降的因素。我们希望在这个项目中获得的对饲养环境、慢性压力和致病性感染之间相互作用的更多理解，将有助于未来设计出最佳的放养系统，从而最大限度地提高鸡蛋产量，同时为母鸡提供最高的福利标准。

Eggs are a very popular source of protein and provide many nutrients that are an essential part of the human diet, therefore it is essential that egg production is safe and sustainable. There is also demand from consumers to improve the welfare of the millions of hens that are kept for commercial egg production, which has led to battery cages being banned in the EU and has encouraged the industry to shift towards keeping hens in cage-free systems. While this is popular with consumers, free range systems introduce new welfare issues for hens which are not yet fully understood. This project aims to investigate the factors which contribute to chronic stress and increased susceptibility to pathogenic infections of hens in free range systems.Our lab has recently validated adult hippocampal neurogenesis as a novel biological marker of chronic stress in the avian brain. Hens who have experienced chronic negative welfare states such as feed restriction (Robertson et al, 2017) or chronic pain from keel bone damage (Armstrong et al, submitted) generate fewer new neurons in the hippocampus during adulthood. In order to compare the effects of different housing environments and health conditions on the level of chronic stress experienced by hens, we will collect brains and process these for immunohistochemistry, then count newborn neurons in order to quantify neurogenesis. We predict that in birds who have lived under more stressful conditions there will be fewer newly generated cells in the hippocampus than in birds who have lived under less stressful conditions.An example of a health condition that we will investigate is footpad dermatitis (FPD). We hypothesise that the pain from FPD causes chronic stress, and will test this by comparing neurogenesis between birds who have severe FPD and those in which FPD is absent. We also propose to use neurogenesis to compare the chronic stress experienced by hens that have been housed in different aviary types. For example, we propose to compare neurogenesis in hens kept in multi-tier systems with those kept in flat deck systems. We may also compare birds who have constant access to cover with those who do not have access to cover whilst on the range.It is known that chronic stress can reduce the effectiveness of the immune system, which increases the probability of infection by pathogens. This is a further welfare concern, and is also an issue for food security because infection by pathogens such as Salmonella enterica can compromise the safe and sustainable production of eggs. We will collaborate with the University of Liverpool to further investigate the interactions between chronic stress and pathogenic infection. We propose to induce chronic stress in laying hens, which will allow us to study the effect of chronic stress on susceptibility to infection, and on the brain.During this project we will also be collaborating with our CASE partner, The Lakes Free Range Egg Company, who will provide us with access to over 1.5 million hens housed in a range of different aviary types. They will assist with the selection of housing environments to compare in order to direct our project towards the production of commercially relevant results. They will also provide historical health and welfare data gathered on their farms over a number of years. During their placement the student will analyse this data in order to determine factors which may predict poor welfare or egg production.We hope that the increased understanding of the interactions between housing environment, chronic stress, and pathogenic infections which will be gained during this project will contribute to the future design of an optimal free range system which maximises egg production while providing the highest possible welfare standards for hens.