Osteoporosis and associated keel bone fractures represent one of the most prevalent and under-recognized welfare problems in laying hens globally. Modern high-producing hens deposit calcium into eggshell at rates exceeding their dietary calcium retention capacity, leading to structural bone loss, keel bone damage, and chronic pain.
Laying hens produce eggs containing approximately 2g of calcium per shell. A high-producing hen may lay 300+ eggs annually, requiring 600g+ of calcium for shell production alone. When dietary calcium is inadequate, hens mobilize structural (cortical) bone calcium, weakening the skeleton. Medullary bone — a calcium reservoir specific to laying hens — provides some buffering capacity but is insufficient to prevent skeletal demineralization in high-producing strains.
The keel bone (sternum) is particularly vulnerable to fracture in laying hens. Fracture prevalence varies by housing system — studies find 50-80% of hens in aviaries and free-range systems have keel bone fractures, compared to 30-50% in enriched cages. Counter-intuitively, more active housing systems show higher fracture rates due to collision injuries during flight.
Keel bone fractures cause chronic pain — hens with fractured keels show reduced activity, altered posture, reduced perch use, and changes in feeding behavior consistent with pain. Pain scoring using the Grimace Scale reveals elevated pain indicators in hens with severe keel bone damage.
With approximately 4 billion laying hens globally, and fracture prevalence of 50-80% in many production systems, the welfare scale of keel bone fractures is enormous — potentially 2-3 billion hens experiencing chronic pain at any given time. This makes keel bone fractures one of the highest-priority welfare issues in livestock production by sheer scale of animal suffering.
Research has identified multiple prevention approaches:
While NSAIDs reduce pain in individual hens with fractures, commercial-scale analgesic administration to laying flocks is not yet practically implemented. Research establishing welfare benefit and practical delivery methods for flock-level analgesia is an urgent welfare research priority given the scale of the problem.