The genetics of modern laying hens have been intensively selected for egg production, with significant welfare consequences including osteoporosis, feather pecking susceptibility, and keel bone fractures.
The genetic legacy of intensive selection for egg production has created hens that are physiologically compromised in ways that fundamentally affect their welfare. Osteoporosis from calcium depletion for eggshell formation makes fractures common and painful. Keel bone fractures, which are almost universal in cage-free systems, cause chronic pain that affects behaviour, movement, and nesting. These genetic welfare problems cannot be fully resolved by housing improvements alone, as they are intrinsic to the birds. Breeding for welfare traits including bone strength, stress reactivity, and feather pecking tendency is scientifically achievable and some breeding companies are making progress. However, progress is limited by the fact that productivity and welfare traits are often in genetic conflict, requiring deliberate investment in welfare-oriented breeding programmes that may reduce short-term production efficiency.