Infectious disease in poultry causes enormous welfare harm, and biosecurity measures that prevent outbreaks protect both animal welfare and public health.
Biosecurity represents a welfare intervention as much as a disease control measure: preventing disease prevents the acute welfare harm of infection and the more significant welfare harm of mass culling. Culling methods used during outbreak response — whole-house gassing, foam suffocation — can cause suffering if not executed properly. The welfare case for preventing outbreaks through rigorous biosecurity is clear: disease prevention is always preferable to outbreak response from a welfare perspective.