Mortality and causes of death in layer strains Lohmann Selected Leghorn and Lohmann Brown kept in small group housing systems and furnished cages

Mortality and causes of death were registered over two laying periods (from July 2002 to July 2003 and from September 2003 to June 2004) in a total of 13045 Lohmann Selected Leghorn (LSL) and 4410 Lohmann Brown (LB) laying hens kept in small group housing systems and furnished cages. The small group housing system Eurovent 625+a-EU was designed for groups of 40 and 60 hens and the furnished cages Aviplus and Eurovent 625A-EU were designed for groups of 10 and 20 hens. In the first laying period 4405 LSL and 4410 LB laying hens were housed from 19th (LSL) and 17th (LB) until 71th (LSL) and 69th (LB) week of age. In the second laying period 4320 LSL laying hens reared in floor husbandry and 4320 LSL laying hens reared in conventional cages were housed from 18th until 57th week of age. Mortality was significantly influenced by housing system and varied from 3.73 % in Aviplus to 5.25% in Eurovent 625+a-EU. In Eurovent 625A-EU 4.15 % of the hens died. In addition, mortality was significantly affected by the interaction between housing system and rearing method. For the LSL laying hens reared in conventional cages, there were no significant differences between the three housing systems examined. In contrast to this, mortality of the floor reared LSL laying hens was significantly greater in the small group housing system Eurovent 625+a-EU (5.50 %) than in the furnished cage Aviplus (3.03 %). In the second laying period, mortality was significantly greater in floor reared LSL laying hens (7.82 %) than in the LSL laying hens reared in conventional cages (2.10 %). Group size also had a significant effect on mortality. Most hens died in the small group housing system Eurovent 625+a-EU with group sizes of 40 and 60 hens per cage (5.58 % and 4.93 %, respectively) and in the furnished cage Eurovent 625A-EU (5.29 %) with a group size of 20 hens per cage. Differences between layer strains LSL (4.52%) and LB (4.87 %) within the first laying period were not significant. The most frequent findings at autopsy were different kinds of cannibalism (65.51 %), whereby cloacal cannibalism (38.57 %) most frequently occurred.

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