The welfare of laying hens in conventional cages and alternative systems: first steps towards a quantitative comparison

Rafael Freire, Ann Cowling

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


Research synthesis, using techniques such as meta-analysis to combine the results of a number of studies, is a particularly usefultechnique when there are multiple studies with conflicting results, or where there may be conflicting interests, and can serve to extractthe maximum information from animal experiments. The effect of conventional cages and alternative housing systems on measures ofproduction, behaviour, physical and physiological condition in laying hens is an important question that would benefit from researchsynthesis. We found that statistical constraints did not allow the usual methods of meta-analysis, so as a first step towards quantitativecomparison, we used a simple vote-counting approach based on the treatment means. We counted the number of papers in whichconventional cages or alternative systems had a higher weighted mean for various response variables. Egg production was higher inconventional cages than in alternative systems, though this effect was probably mostly confined to the comparison with multi-level indoorsystems. Bones were stronger from hens kept in alternative systems than those kept in conventional cages. We confirmed previousreviews that birds show more comfort behaviour and possibly dustbathing (or vacuum dustbathing) behaviour in alternative systems, butaggressive pecking did not differ between systems. Perhaps surprisingly, mortality, feather pecking and body wounds were not found todiffer between systems. The latter findings suggest that the chance of a mortality or cannibalism outbreak may be no greater in alternativesystems than in cage systems, but it should be noted that our analysis did not consider the magnitude of the difference in mortality.In conclusion, the meta-comparison undertaken here supports some but contradicts other conclusions reached in qualitative reviews.
Original languageEnglish
Pages (from-to)57-65
Number of pages9
JournalAnimal Welfare
Issue number1
Publication statusPublished - Feb 2013


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