Laying Hen Welfare and Corticosterone Levels |
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A recent Australian study led by Jeff Downing at Sydney University measured stress in egg-laying hens and found no difference in corticosterone levels in the eggs of free-range and caged hens. Corticosterone is a hormone that can be detected at increased levels in the blood during excitement or stress, and it is sometimes measured during experimental analysis of the welfare of chickens and other birds.
The findings released by the recent Australian study are not convincing evidence that the welfare of hens in cage production systems is similar to the welfare of free-ranging hens. A much more thorough analysis of the stress experienced by laying hens in cages and in cage-free systems was recently undertaken in a program funded by the European Commission, the LayWel project(1)—a collaborative effort by working groups in seven European countries that accumulated data from 230 different laying hen flocks. At the end of their study, the members of the project concluded that "with the exception of conventional cages, all systems have the potential to provide satisfactory welfare for laying hens" (emphasis added).
As part of its comprehensive assessment of the well-being of laying hens, one working group in the LayWel project compiled data on a variety of stress measures from 16 independent experiments and found that measures were highly inconsistent, clearly demonstrating the fundamental problem with using a single measure of stress as the sole indicator of animal well-being.
Understanding the complexity of interpreting stress measures is not new. Dr. Jeff Rushen with the Department of Animal Sciences at the University of Alberta in Edmonton has stated, "Claims about animal welfare based on data regarding the pituitary-adrenocortical axis [the physiological stress response system] should be viewed with skepticism because of the lack of consistency between the results of different studies."(2)
Indeed, many factors influence stress levels. For example, hens in free-range systems need adequate cover for protection from predators. If hens in the cage-free system in the Australian study were kept on open pasture without access to shelter or another form of protective covering, they were likely more stressed than hens would be in well-managed outdoor systems that provide hiding places where hens could seek refuge. Using an environment known to cause stress to laying hens—a wide open area with no cover—to make a judgment about all cage-free systems is misleading.
An in-depth analysis of animal welfare requires a holistic approach that considers, in addition to measures of stress, productivity, health, disease, mortality rates, environmental parameters, and, above all, a detailed analysis of behavior. Hens in cages suffer from behavioral deprivation; they are unable to roost, scratch the ground, dustbathe, lay their eggs in a secluded nest, or perform a number of other behaviors that are important to them. We know that the expression of these behaviors are essential to good welfare because an extensive, detailed scientific body of literature devoted to the study of animal behavior has determined that hens, like other animals, have behavioral needs that, when thwarted, result in the lack of a pleasurable existence, at least, and more likely acute daily suffering.
The LayWel project conducted a thorough analysis of laying hen welfare using the holistic approach and included a working group dedicated to the assessment of laying hen behavior in conventional cages and alternative systems. They concluded by stating:
Conventional cages do not allow hens to fulfil [sic] behaviour priorities, preferences and needs for nesting, perching, foraging and dustbathing in particular. The severe spatial restriction may also lead to disuse osteoporosis. We believe these disadvantages outweigh the advantages of reduced parasitism, good hygiene and simpler management. The advantages can be matched by other systems that also enable a much fuller expression of normal behaviour. A reason for this decision is the fact that every individual hen is affected for the duration of the laying period by behavioural restriction. Most other advantages and disadvantages are much less certain and seldom affect all individuals to a similar degree.(3)
Dr. Michael Appleby, one of the world's leading poultry welfare experts, writes:
Battery cages present inherent animal welfare problems, most notably by their small size and barren conditions. Hens are unable to engage in many of their natural behaviors and endure high levels of stress and frustration. Cage-free egg production, while not perfect, does not entail such inherent animal welfare disadvantages and is a very good step in the right direction for the egg industry.(4)
In short, the problem with battery cages is that the potential for high welfare is limited by the inherent restriction of movement—and denial of important behaviors—imposed by the confines of the enclosure. It is impossible to provide for the behavioral well-being of a hen crowded in the barren, battery cage environment.
Animal advocates seek to raise the bar when it comes to animal welfare. Battery cages limit the height at which that bar can be set. The push toward cage-free systems for laying hens is not based on "aesthetics," rather, it is grounded in both solid scientific assessment of what is best for the welfare of hens and on legitimate ethical analysis.
1. Blokhuis HJ, Fiks van Niekerk T, Bessei W, Elson A, Guemene D, Kjaer JB, Maria Levrino GA, Nicol CJ, Tauson R, Weeks CA, and van der Weerd HA. 2007. The LayWel project: welfare implications of changes in production systems for laying hens. World's Poultry Science Journal 63:101-14.
2. Rushen J. 1991. Problems associated with the interpretation of physiological data in the assessment of animal welfare. Applied Animal Behaviour Science 28:381-6.
3. Blokhuis HJ, Fiks van Niekerk T, Bessei W, Elson A, Guemene D, Kjaer JB, Maria Levrino GA, Nicol CJ, Tauson R, Weeks CA, and van der Weerd HA. 2007. The LayWel project: welfare implications of changes in production systems for laying hens. World's Poultry Science Journal 63:101-14.
4. Appleby M. 2006. Clarification. Letter to the editor. The Minnesota Daily, February 7. www.mndaily.com/articles/2006/02/07/67009
Related Links
An HSUS Report: The Welfare of Animals in the Egg Industry
Scientists and Experts on Battery Cages and Laying Hen Welfare
An HSUS Report: Welfare Issues with Selective Breeding for Production in Egg-Laying Hens
