Keel bone fractures affect the majority of hens in some cage-free systems, causing chronic pain that represents a significant welfare challenge in the transition away from cages.
Keel bone fractures represent a serious and underappreciated welfare problem in the transition to cage-free poultry housing. The irony is that systems developed to improve hen welfare by allowing natural behaviors including perching and flight have introduced a new welfare problem through the fractures that result from falls and collisions in multi-level environments. Hens with keel bone fractures show behavioral changes consistent with chronic pain - reduced activity, altered posture, and reluctance to use perches. The prevalence in some aviary systems is so high that cage-free systems may create a net welfare negative for a significant proportion of hens compared to battery cages, despite providing other welfare benefits. Solutions including lower perch heights, perch textures that improve grip, landing areas, and selective breeding for bone density aim to address the problem while preserving the welfare benefits of cage-free housing.