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Are stress levels of caged layer hens the same as those of hens in non-cage egg production systems?
The egg industry claims that caged hens are no more stressed than free-range or barn-housed hens. However, the author of the industry-commissioned research from which this claim derives, draws the following slightly different conclusion (The University of Sydney, 2012) “…comparisons between systems are of less significance to the hen than what is happening within her housing environment.”
The unpublished research analysed the hen’s stress hormone (corticosterone) in egg albumen (the clear liquid or egg white contained within the egg) and found that differences in corticosterone levels had to do with how the birds on a particular farm were managed and what challenges (physiological and environmental) they had to cope with.
Using non-invasive markers of stress, such as corticosterone in egg albumen, is preferable to more traditional methods such as blood sampling where the handling of the bird in itself will result in a certain level of stress. However, the use of corticosterone in the absence of other data and without being able to link this to individual birds is always going to be of limited value.
Chronic housing stress is better examined using several physiological, behaviour and production measures. An example is El-Lethey et al., (2000), who showed a range of effects, including lower stress levels, in floor housed hens provided with straw compared to hens not provided with straw. This study also illustrated that housing effects on physiology are not restricted to the housing per se but to the provisions provided. Nicol et al. (2011) have taken this approach further and suggest that the taking of a range of measures, including physiology, should be evaluated to make sure that different measures are not measuring the same thing.
The RSPCA believes that poor hen welfare is inherent to cage systems regardless of how they are managed. All layer hen housing systems have their advantages and disadvantages. However, the disadvantages of cages can only be overcome by fundamentally changing the housing system. With free range and barn the disadvantages can be overcome by improved management.
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