Perch access in laying hen housing systems dramatically improves bone density, reduces keel bone fractures, and supports natural roosting behaviour that hens are strongly motivated to perform.
Keel bone fractures represent perhaps the most widespread and underappreciated welfare crisis in farm animal production. Affecting the majority of laying hens in commercial systems, these fractures cause chronic pain throughout the laying cycle. Hens with keel fractures show reduced perch use, altered feeding behaviour, and responses on cognitive bias tests consistent with a negative emotional state. The bones of modern laying hens are chronically depleted of calcium that is redirected to egg production, making them highly susceptible to fracture. Perch access alone is insufficient to solve the problem; genetic selection away from extreme egg production rates and housing that allows normal wing-flapping and landing behaviour are also required. The scale of this welfare problem — affecting billions of individual animals — and its chronic, painful nature make it a priority for welfare science and advocacy attention.