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Table 6 Risk analysis regarding main disease categories between laying hen flocks in cages1 and free range housing2.

From: Causes of mortality in laying hens in different housing systems in 2001 to 2004

Disease category Observed no. of flocks from free range housing Expected no. of flocks if same risk as in cages Excess no. of flocks in free range housing compared to cages
Bacterial diseases 17 1 16***
Viral diseases 1 1 0
Parasitic diseases 5 0 5***
Cannibalism 6 0 6***
Total 23 2 21***
  1. 1Includes conventional battery cages and enriched cages.
  2. 2Flocks housed in litter-based systems indoors, with access to outdoor pens and pasture, including organic flocks.
  3. Levels of significance are denoted by *** P < 0.001