Why do hens smother? An investigation into the causes and consequences of smothering

There can be no egg farmer who wants to walk into a chicken house and find a pile of dead birds, only to know the same event could happen again tomorrow and the next day, without being able to prevent it. This is the impact of smothering, a strange behaviour whereby hens pile on top of each other causing deaths of chickens at the bottom of the pile. No-one really understands why chickens do this and often they appear to move slowly and calmly in the lead up to smothering. Naturally, farmers who produce eggs would like to reduce this behaviour, but it doesn't happen when they are present in the farm watching the birds. It happens intermittently and is hard to predict. New approaches are therefore urgently needed to understand this behaviour. The behaviour and motivations of birds during these smothering events is of great interest to scientists because animals don't often cause the death of other animals of the same species in such an apparently calm manner. This research aims to investigate when, where and how smothering happens, and the effect smothering has on the chickens that survive. The fact that smothering is unpredictable means that a large number of farms are needed in order to study this behaviour. Working with an egg producing company we will have access to 110 flocks of birds. These all have a monitoring system, Birdbox, which records information about the environment of the hens (e.g. ventilation and temperature), food and water intake, egg production, and numbers and causes of hen deaths. We will also gather further information on whether these chickens were stressed when they were still chicks, details of the barns where they live, at what time smothering events occur and where in the barn they happen. All this information will be used find the potential causes of smothering and to see if there could be early warning signs before it happens. Whilst useful for understanding the development of smothering behaviour, these analyses by themselves won't identify the immediate cues that cause chickens to move in ways which smother others, or indeed what movements cause smothering. To address this we will place heart rate monitors on chickens and film smothering events using thermal and standard cameras. The thermal cameras will allow us to automatically measure movements of chickens to be able to create a realistic simulation of smothering. The simulation of smothering will allow us to understand what it is about hen's movements which means other hens don't move out the way and end up getting killed. Heart rate monitors will enable us to see whether stress might trigger smothering, or whether birds really are as calm as they appear when starting to smother one another. We will also measure other indications of a stressed flock and hen welfare: fearfulness toward humans and novel objects, stress hormones in the egg, faults in eggshells and bone injuries. It is important to understand smothering behaviour because it harms chickens welfare and causes deaths of 1.4% of birds in a flock die from smothering (this equates to 21% of all mortalities) and can kill more than 20% of hens in badly affected flocks. Whilst 1.4% overall may sound small, this equates to over 300,000 hens deaths and 86 million eggs lost across the UK egg farms. The real impact of smothering is probably much greater than this because often hens killed by smothering will not be recognised as such. In addition, the potential for injuries and stress in those that survive have never before been investigated. Our results will be used to understand what causes this behaviour which will help farmers know how to intervene to prevent smothering. Our results will be able to reveal if information in the BirdBox could provide a warning that smothering is imminent, or whether particular movements made by hens might be useful for early warnings of smothering. Through this project we will benefit by understanding the true impact of smothering for laying hen welfare.

We will undertake the first comprehensive study of smothering in this industry partnered LINK grant. Smothering is an aberrant collective behaviour which causes 21% of mortality in laying hens through piling of birds on top of one another in a concentrated area. We focus on risk factors and mechanisms involved in 'creeping smothers', which occur in open spaces, with slow bird movement and in the absence of any obvious trigger. In an exceptional opportunity, this project will have access to 110 flocks of laying hens equipped with systems to automatically collect real-time data on environmental, resource use and productivity parameters. Additional data will be collected on early life stress and stressors. This data will be used for an epidemiological analysis of risk factors for smothering events (using marginal structure models to estimate historical and current influences). The mechanisms of smothering will be studied using two approaches: simulations of smothering using agent based models; and measuring behaviour and physiology of birds before, during and after smothering events. Flocks which show high levels of smothering will be filmed using thermal cameras, to track chicken movements during smothering events. Trajectories of movements from individual birds will be used to build and test simulations. Chickens in high smothering flocks will also be fitted with heart rate monitors, and after a smothering event, egg albumen corticosterone levels, novel object tests, egg shell irregularities, and keel bone injuries will be measured and compared to age-matched, low smothering flocks. These parallel approaches will reveal local cues of bird movement which result in smothering, the arousal state of birds performing the behaviour, and the welfare consequences of smothering for hens that survive. The project will offer practical and theoretical insights into this welfare concern which costs the UK poultry industry more than £6.5million/yr and 86 million eggs.

The main benefits of this project are, understanding: 1) the causes smothering, 2) the potential for early warnings of smothering, 3) the cost and welfare impact of smothering. The project supports future use of sensors (image, thermal and wearables) and sensor management systems for livestock. Key beneficiaries are: non-cage egg producers, retailers, assurance schemes & policy makers, the public, and livestock monitoring & technology companies. There will be considerable benefits to hen welfare.

UK non-cage egg producers (3242 farms/24million hens, ~60% of the market) are the primary beneficiaries of this research. For badly affected flocks in non-cage housing, smothering can result in mortality of over 20%; on average it costs more than £3535/flock annually or £6.5 million across the UK. We will identify risk factors of smothering, so producers can implement changes to reduce occurrence. We will provide knowledge of the causes of smothering which is needed to design appropriate interventions, as current methods are ineffective. It is likely that deaths by smothering and other impacts are vastly underestimated. This project will provide producers with information on welfare and cost impacts of smothering to empower them to devote resources accordingly. Smothering also has an emotional impact on many producers when they find a pile of dead hens knowing they are unable to predict or effectively control the problem. We will identify potential methods for predicting outbreaks of smothering, using environmental variables in BirdBox and hen movement patterns which could be automatically detected. UK farmers are under pressure to improve animal welfare, sustainability and environmental impacts, whilst turning a healthy profit. Reducing smothering increases profits and improves animal welfare. Hen health and use of antimicrobials would be improved by reducing stress or injuries caused by smothering. Lower hen mortality and stress would result in more sustainable production. Global trends predict a 45% increase in a global non-cage egg industry worth $6559 million by 2025. Smothering will be a new problem for producers changing from cage to non-cage systems. Therefore secondary beneficiaries for this project will be new egg producers globally.

Retailers will benefit from the project by enhancing their reputation for retailing high welfare products, through sales of eggs from farms where smothering had been reduced. Key retailers, M&S and McDonalds, support this project through dissemination activities.

Assurance scheme providers and Policy makers will benefit from the research by incorporating information on smothering and mitigation strategies into their welfare assessment protocols or certification standards for laying hens. RSPCA Assurance, Soil Association, and Lion code Defra and Animal Health and European Food Standards Agency, EFSA are the key organisations which stand to benefit.

Animal welfare organisations such as the RSPCA, Compassion in World Farming, and the Laying Hen Welfare Forum (LHWF) will benefit from additional information on smothering to help them protect the welfare of hens.

The Public has displayed high consumer demand for high welfare eggs yet smothering occurs more in high welfare systems. Information on smothering is not generally available to the public and this project will help raise awareness.

Livestock monitoring and technology companies will benefit from this research in two ways. Firstly through demonstration of the value of monitoring systems for understanding association with health and welfare concerns. Use of the monitoring system for epidemiology research in this project will support utilisation and uptake of these systems in the future. Secondly, through value demonstration and development, this project will support future Precision Livestock Farming application of animal tracking, wearables for monitoring sentinel animals, and acoustic monitoring.