Welfare of Laying Hens in Conventional Cages and Alternative Systems: First Steps Towards a Quantitative Comparison19 November 2013
Reviewing published studies comparing the welfare of hens kept in conventional cages with alternative systems, researchers in Australia found that birds in cages had higher egg production. Bones were stronger in those birds in alternative systems, which also allowed more comfort behaviour, such as dust-bathing. No differences in aggressive pecking, feather pecking, mortality or body wounds were found between the systems.
Research synthesis, using techniques such as meta-analysis to combine the results of a number of studies, is a particularly useful technique when there are multiple studies with conflicting results, or where there may be conflicting interests, and can serve to extract the maximum information from animal experiments, according to R. Freire and A. Cowling at the School of Animal and Veterinary Sciences of Charles Sturt University in Wagga Wagga, Australia.
In a paper in the journal, Animal Welfare, they explain that the effect of conventional cages and alternative housing systems on measures of production, behaviour, physical and physiological condition in laying hens is an important question that would benefit from research synthesis.
They found that statistical constraints did not allow the usual methods of meta-analysis, so as a first step towards quantitative comparison, they used a simple vote-counting approach based on the treatment means. They counted the number of papers in which conventional cages or alternative systems had a higher weighted mean for various response variables.
Egg production was higher in conventional cages than in alternative systems although this effect was probably mostly confined to the comparison with multi-level indoor systems.
Bones were stronger from hens kept in alternative systems than those kept in conventional cages.
The researchers confirmed previous reviews that birds show more comfort behaviour and possibly dustbathing (or vacuum dustbathing) behaviour in alternative systems but aggressive pecking did not differ between systems.
Perhaps surprisingly, mortality, feather pecking and body wounds were not found to differ between systems. The latter findings suggest that the chance of a mortality or cannibalism outbreak may be no greater in alternative systems than in cage systems but the authors noted that their analysis did not consider the magnitude of the difference in mortality.
Freire and Cowling concluded that the meta-comparison undertaken in Wagga Wagga supports some but contradicts other conclusions reached in qualitative reviews.
Freire R. and A. Cowling. 2013. The welfare of laying hens in conventional cages and alternative systems: first steps towards a quantitative comparison. Animal Welfare. 22: 57-65. doi: 10.7120/09627286.22.1.057