Flock Factors Correlated with Elevated Mortality in Non-Beak Trimmed Aviary-Housed Layers

SIMPLE SUMMARY: There is increasing use of non-cage housing systems for laying hens in Europe. In Norway, approximately 85% of all hens are housed in aviaries. Such systems are more complex and house larger animal groups. Knowledge of flock level factors that may affect mortality in these systems is important to be able to improve animal welfare, reduce mortality and enhance sustainability. The aim of this study was to investigate factors that may contribute to mortality in non-beak trimmed aviary-housed laying hens in Norway. Overall, the investigations found an association between elevated mortality and increased feather loss, which may be an indication of feather pecking and cannibalism. ABSTRACT: The use of non-cage housing systems for layers is increasing in Europe and elsewhere. Knowledge of factors that may affect mortality in these systems is important to be able to improve animal welfare, reduce mortality and enhance sustainability. The aim of this study was to investigate factors that may contribute to increased mortality in non-beak trimmed aviary-housed laying hens in Norway. A total of 39 non-beak trimmed commercial flocks (Lohmann LSL (n = 25) and Dekalb White (n = 14)) were visited between week 70 to 76 of life, and factors related to health, behaviour and management were recorded. Mean mortality in the flocks was 3% (range: 0.5–9%) and increased flock mortality was correlated with total feather loss (p < 0.05); feather loss on the breast (p < 0.02) and feather loss on the head (p < 0.003). There was an association between layer hybrid line and mortality (p = 0.055). Furthermore, a low positive correlation between mortality and dust level inside the barn was found (p < 0.04), showing that mortality was higher when dust level was also high. No correlation between mortality and the provision of environmental enrichment was found. In conclusion, this study found an association between flocks with elevated mortality (>3.0%) and increased feather loss which may indicate feather pecking. The results underline the importance of regularly assessment of plumage condition in commercial layer farms, as a tool to detect early signs of feather pecking in commercial aviary-housed layer flocks. This may help to target feather pecking before cannibalism breaks out.