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

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

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***

¹Includes conventional battery cages and enriched cages.
²Flocks housed in litter-based systems indoors, with access to outdoor pens and pasture, including organic flocks.
Levels of significance are denoted by *** P < 0.001

ISSN: 1751-0147