Implications for Welfare, Productivity and Sustainability of the Variation in Reported Levels of Mortality for Laying Hen Flocks Kept in Different Housing Systems: A Meta-Analysis of Ten Studies.

All variables show highly significant associations with CM, which increased with age; decreased with flock size; was highest in flocks of intact beaked birds and organic flocks; and varied with both housing system and breed.

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For example a recent comparison of 9 cage flocks with 8 flocks housed in barns in Canada found a consistent trend at all ages for lower mortality in cages than barns but this did not reach statistical significance [ 26 ].

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