Laying hen welfare -The prevention of feather pecking and keel bone damage

Feather pecking (FP) and keel bone damage (KBD) are important animal welfare problems in laying hen housing, in both organic and conventional systems. This PhD project aimed (1) to give an overview over results from scientific studies regarding factors with preventive effects on FP, and on the extent practice recommendations are based on this scientific evidence; (2) to identify further influencing factors on FP and to test the significance of the extent of compliance with recommendations; and finally (3) to discover management and housing factors that are associated with KBD in organic laying hens. From scientific publications of controlled experiments as well as epidemiological studies, 17 factors during rearing, and 32 factors during the laying phase were identified that were found to significantly affect the risk of FP or plumage damage. In the reviewed 15 practice recommendations, almost all of these factors have been taken up, although no recommendation comprises all factors and most miss more than half of them. This leaves ample room for improvement, while recommendation of 15 contentious as well as eight non-significant or 12 not yet investigated factors calls for further scientific investigation. A case-control study based on pooled data from three cross-sectional studies resulted in a regression model with four factors, based on 137 flocks, that explained 41% of the variance and correctly classified 77% of cases. A higher stocking density, and unexpectedly a higher drinking place/hen ratio, increased the likelihood of a ‘FP-problem’, the presence of wooden perches and a littered veranda lowered it. The results concerning wooden perches and drinking place/hen ratio might be due to indirect effects and should be further investigated. In non-FP flocks significantly more recommendations were fulfilled (on average 46.5%) than in FP flocks (42.5%). Thus, both the number of fulfilled recommendations and the combination of specific measures appear to be important. The analysis of cross-sectional data concerning factors associated with KBD in organic hens resulted in a regression model, based on 50 flocks, that comprised four factors and explained 32% of the variation in KBD between farms. Aviary vs. floor systems, absence of natural daylight in the hen house, high proportion of underweight birds as well as a high laying performance were found to be significantly associated with an increased number of KBD cases. In order to achieve a better understanding of the relationships between laying performance, feed management and KBD further investigations are needed.