Laying hen mortality in different indoor housing systems: a meta-analysis of data from commercial farms in 16 countries.

For both France and the Netherlands, no temporal trends in mortality were detected for caged systems, but there was a highly significant drop in mortality over this period in the cage-free aviaries, with year of data collection accounting for 73% and 58% of the variability in mortality reported in the two countries, respectively (Fig. 5 ).

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