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Quantifying the subjective state of feed restricted broiler chickens using behavioural and neurochemical measures - AW1141

Chickens which are reared for meat production (broilers) have been selected over many generations primarily for rapid growth until slaughter at 5 or 6 weeks old. The parent stock of these birds (referred to as broiler breeders) are typically kept for reproduction to 60 weeks of age also have the capacity to grow rapidly. If fed to appetite, these birds become obese, resulting in a number of health and welfare problems, and poor egg production. Consequently, broiler breeders are routinely feed-restricted to around 40% of the feed they could eat. The undesirable side effect of this rationing is hunger and mis-directed oral behaviours, which may represent an issue for animal welfare. However, broiler breeders still grow and reproduce despite this restriction, and wild animals frequently encounter periods of reduced food resources, or periods when they reduce their food intake naturally, suggesting they can adapt to feed restriction.

Animal welfare is fundamentally about how animals feel (that is, their 'subjective state'), and methods aimed specifically at measuring feelings have not been applied to the question of feed restriction in broiler breeders before. In this proposal, we will apply two approaches, separately and then in combination, to measure the subjective state of broiler breeder chickens, feed restricted at commercially-applied levels:

1) Conditioned place preference/aversion (CPP/A). These techniques are widely used in pharmacology, and there is good evidence that they could be used to quantify how a chicken feels overall about an environment where it is feed restricted in contrast to an environment with a more generous feed allowance but where it must endure some other negative aspect of housing. Chickens will be trained over several days that in one visually-distinctive location, commerical feed restriction will occur, and in another location a more generous feed allowance will be provided, but in combination with some factor known to reduce chicken welfare (e.g. small space allowance, social isolation, no litter provided). Once trained, chickens will be allowed to choose between the two locations, in the absence of any feed or negative factors- just the visually distinctive cues of those locations. This is important, as tests of food motivation which involve offering more food can change the chicken's perception of the situation profoundly. Depending on the findings, this approach will enable us to make a statement such as “Chickens experience of commercial feed restriction is so negative that they prefer an environment where 10% extra feed comes at the cost of confinement in a small space, equivalent to that provided to battery hens.”. The comparison across different negative factors (hunger and e.g. reduced space) makes it possible to quantify the negative feelings associated with feed restriction in comparative terms which are easy to understand so that a wider ethical debate is then possible.

2) Neurochemical measurements of negative subjective states. Humans suffering from anxiety and depression show characteristic neurochemical changes. Similar changes have been found in rodent and poultry models of these negative states (for example they can be induced by social isolation). A neurochemical marker known to correspond closely to feeding motivation in poultry will also be investigated. To further validate these measures in relation to feed restriction, we will use a line of hens which show incubation ('broody') behaviour when they are left with their eggs. Broodiness results in a natural reduction in feed intake and body weight loss. Since broody hens lower their feed intake voluntarily, we would expect these birds to be in a normal or positive subjective state in contrast to non-incubating hens of the same line where a similar level of feed-restriction is imposed. We expect our neurochemical measures of negative subjective states to reflect this. Findings from broody/non-broody birds will be compared to the results obtained from broiler breeders at different levels of restriction to quantify their subjective state. Depending on the findings, it will enable us to make a statement such as “Chickens under commercial feed restriction show neurochemical changes of a similar type and degree to those in anxious or depressed humans.”

In a final step, the two approaches will be combined. The CPP/A approach enables us to identify environments with combinations of negative factors and feed allowance which chickens perceive as the same as, better than, or worse than, commercial levels of feed restriction. We will rear chickens in these conditions and determine whether the neurochemical measures of negative subjective states result in the same ranking of environments as the CPP/A approach.

This project brings together a multidisciplinary team of experienced researchers with the necessary expertise covering avian behaviour, cognition and welfare, nutrition and neurobiology, from three organisations each with a strong track-history of high-quality research in the relevant fields. We will employ two novel and complementary approaches, selected for their suitability to address Defra's policy need to quantify the negative subjective state of restricted broiler breeder chickens.
The overall aim of this project is to address Defra’s stated policy need to “assess the impact of commercially relevant feed restriction on the subjective experience of broiler breeders”.

Objective 1: Behavioural measures of the subjective experience of feed restricted broiler breeders (months 0-30)

Objective 2: Neurochemical measures of the subjective experience of feed restricted broiler breeders (months 1-26)

Objective 3: Cross-validation of behavioural and neurochemical approaches (month 31-36)
Project Documents
• EVID4 - Final project report : AW1141 - final report   (1097k)
Time-Scale and Cost
From: 2009

To: 2012

Cost: £706,792
Contractor / Funded Organisations
Roslin Institute, Edinburgh (BBSRC), SAC Commercial Ltd, University - Newcastle
Animal Welfare              
Plants and Animals              
Fields of Study
Animal Welfare