Evaluation of bone strength, keel bone deformity and egg quality of laying hens housed in small group housing systems and furnished cages in comparison to an aviary housing system

As furnished cages will be forbidden in Germany after 2011, research has been stimulated to develop small group housing systems and test their suitability particularly in respect to welfare and health issues. The objective of the present investigation was to assess bone breaking strength, keel bone deformity and egg quality (shell breaking strength) of Lohmann Silver (LS) and Lohmann Tradition (LT) laying hens housed in a small group housing system (Eurovent 625a-EU, group size 40, 60 hens) and furnished cages (Aviplus, group size 10, 20, 30 hens) in comparison to an aviary housing system (model “Natura”, 2 pens, 1215 hens). At the end of the 3rd, 6th, 9th and 11th laying month, approximately 40 hens were randomly chosen from each housing system and slaughtered (478 hens in total). Humerus and tibia strengths were analysed by using a three-point-bending machine (Zwick/Z2,5/TNIS, Zwick-Roell, Ulm, Germany). Keel bone status was evaluated visually and per palpation and was recorded on a scale from 1 to 4 (1 = severe deformity, 2 = moderate deformity, 3 = slight deformity, 4 = no deformity). Every four weeks a sample of eggs was collected (totalling 4887 eggs) and shell breaking strength was measured by applying force (N) to the shell until breakage (Zwick/Z2,5/TNIS). Statistical analyses were performed using the MIXED procedure of SAS, version 9.1.3 (Statistical Analysis System Institute Inc., Cary, NC, USA, 2006). Humerus and tibia breaking strengths of LS layers housed in the EV 625a-EU were significantly higher compared to LS hens kept in the Aviplus. Bone breaking strengths of humerus and tibia in LS and LT layers were highest in the aviary system and the differences to the other housing systems were significant. No significant differences in tibia and humerus bone breaking strengths were found between the EV 625a-EU and the Aviplus for LT hens. Keel bone status was not significantly influenced by housing system or laying strain. For both layers, shell breaking strength was significantly lower in the EV 625aEU compared to the Aviplus and aviary system. The results of the present investigation showed that small group housing systems can significantly enhance bone breaking strength for LS layers in comparison to hens kept in the Aviplus. The lower shell breaking strength of eggs in the EV 625a-EU might slightly impair economic aspects.