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

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.