Broiler gut health and C. jejuni infection: impacts of harvest management

Life-End summary
Sustainable production of safe chicken is an international priority and preserving bird welfare is a key component of this. Current intensive (broiler) production can compromise bird health and welfare and food safety and there are strong links between poor bird welfare and the Campylobacter public health threat. Campylobacter is the most common cause of bacterial diarrhoea in the EU and despite millions of pounds of research funding it is estimated that contaminated chicken caused ~700000 human campylobacteriosis cases in the UK in 2013 with around 100 deaths. Infection is characterised by severe abdominal pain and acute (sometimes bloody) diarrhoea and costs the UK an estimated £1 billion per year. Campylobacter contamination of chicken takes two forms. First, surface contamination of carcasses leads to cross-contamination in the kitchen. Second, and perhaps of greater importance than currently thought, contamination within muscle and liver tissues, increasing the health risk by facilitating bacterial survival during cooking.
Chickens in poor production environments or exposed to stress are more susceptible to Campylobacter and in such birds the bacteria show greater extra-intestinal spread to edible tissues, possibly as a consequence of disturbance to the gut environment. Therefore, improvements in broiler welfare have great potential to improve public health but there is an urgent need for information on the effect of stress to inform targeted interventions to reduce Campylobacter in broiler chickens.
One acutely stressful event in the life of broilers, in any production stream, is harvest when birds are removed from the farm for slaughter. We define the process as comprising: food withdrawal, catching, transport and stunning by either gas or electricity. Although there is a growing body of evidence that these stressors can increase Campylobacter growth rates as well as extra-intestinal spread, there is a paucity of data on their relative importance or how they may select for particular types of Campylobacter.
By examining the harvest processes using large scale industry-relevant experimental conditions, state-of-the-art genomics, molecular microbiology and mathematical modelling techniques, we will determine the impact of harvest on gut health in broilers. We will combine this with a study to identify bacterial genetic determinants involved in extra-intestinal spread of Campylobacter to edible tissues. We will quantify the relative impact of each stage of harvest on the gut bacterial population and the physiology and immunity of the birds, and investigate the role these play in controlling extra-intestinal spread of Campylobacter.
This multidisciplinary research programme will enhance understanding of the influence of the harvest process on bird gut health and Campylobacter. The quantitative information and modelling will be used to provide direct advice to industry about the elements of the harvest processes that provide the best opportunity for interventions that will mitigate the ongoing challenge of Campylobacter contamination in chicken meat.

Life-End technical summary
Preserving bird welfare is a key part of sustainable, safe chicken production. Current intensive production can compromise bird welfare and raises the Campylobacter public health threat; we found strong links between broiler health/welfare and Campylobacter colonisation of chickens. Chicken is the main source of human Campylobacter and this threat must be reduced. There is increasing evidence that edible tissues of chicken, particularly liver, can be Campylobacter-positive. This may be a consequence of bird stress responses and/or colonisation with strains of the bacteria that are inherently better able to leave the gut. Our proposed studies will examine both scenarios and, in novel experiments, we will mimic natural infection and inoculate birds with multiple strains of C. jejuni previously isolated from the chicken gut, carcass surfaces or tissues. These will be characterised using whole genome sequencing and a genome-wide association study to identify genetic elements associated with extra-intestinal spread.
An acutely stressful event in broiler management, in any production stream, is harvest, which we define as comprising four processes: feed withdrawal, catching, transport and stunning. Most UK chickens will be colonised with Campylobacter at harvest and we will study, under controlled commercial conditions, birds colonised with C. jejuni.
We will determine if harvest stresses, individually and collectively, increase extra-intestinal spread of C. jejuni to edible tissues. Our focus is on the gut of the bird and we will examine microbiota, gut epithelial integrity and innate immune responses as well as the in vivo behaviour of the C. jejuni strains. We will use modelling to investigate the relative importance of the underlying biological mechanisms that determine C. jejuni behaviour during the harvesting processes and provide industry with a cost: benefit analysis of different methods of mitigation of the harvest processes.

Life-End impact summary
Sustainable production of safe chicken is an international priority and preserving/improving bird welfare is a key component of this. Current intensive (broiler) production can compromise bird health and welfare and food safety. Our past work found strong links between broiler health and welfare and the Campylobacter public health threat, a powerful argument for maintenance of high welfare in production. Campylobacter is the most important food borne zoonosis in the UK and the wider EU. In the UK it is estimated that there were ~700000 cases of infection in the UK in 2013 and that chicken-associated Campylobacter infection costs the UK economy ~£1 billion per year. Chicken is overwhelmingly the most important vehicle for human infection and is believed to be responsible for up to 80% of infections. ~80% of chickens on sale in the UK are Campylobacter-positive.
Contaminated chicken presents two health threats. Surface contamination levels can be very high and contamination of deep muscle and liver tissues has been reported in up to 27 and 60% of samples tested respectively. Broiler producers need to improve bird welfare and in so doing lower the public health risk from Campylobacter-contaminated carcasses.
One acutely stressful event in the life of broilers, in any production stream, is harvest which comprises feed withdrawal, catching, transport and stunning. Most birds in the UK will be Campylobacter-positive at depopulation The proposed project seeks to address these issues by undertaking a detailed examination of the interactions between bird gut health and the infection biology of C. jejuni and how these are affected by harvest processes. One key outcome of stress on chickens is that Campylobacter can show extra-intestinal spread and contaminate edible tissues. In addition, levels of the bacterium in the gut increase meaning that carcass contamination may also be higher. It is important to know which of the harvest processes are most important in these respects so that interventions can be better identified.
The work will also determine which is the more important in the spread of C. jejuni from the gut to edible tissues: an apparent enhanced ability to leave the gut as shown by some C. jejuni strains and/or host stress responses. We have evidence to support both. Our past work found that when C. jeuni was cultured in the presence of noradrenaline (NA) before being given to chickens it showed a high level of extra-intestinal spread being recovered with high frequency from deep liver tissues.
The international broiler chicken industry accepts that changes to harvest processes may be needed but requires research outputs in order to identify the key points where change is needed. It is not possible for the industry to undertake this research on its own. It is important that any change is science-led and that all relevant aspects are considered. For example, the move from electrical to gas stunning on welfare on welfare grounds may have increased the public health threat from chicken meat. Gas stunned animals can have high circulating levels of NA and we hypothesise that this could facilitate the process by which C. jejuni leaves the gut and contaminates tissues.
We seek to lessen the public health and bird health threats associated with harvest regimes. The project is in partnership with the UK poultry industry and we will form a project steering group comprising senior UK academics and, more importantly, people from poultry companies and major UK retailers. When he was in Liverpool the work of the PI (TH) on Campylobacter and chickens was co-funded by all major UK retailers. The regular update meetings with these organisations will continue. Through this and the project steering group, the beneficial impacts of our work can quickly be transferred to stakeholders, both those with direct involvement in this work and in the wider community.