Equine influenza biosecurity at yards and events prevents outbreaks that cause significant welfare harm across horse populations.
Equine influenza outbreaks cause welfare harms at both individual and population levels. Each affected horse experiences significant respiratory illness; population-level outbreaks affect the movement and management of thousands of animals. The 2007 Australian outbreak — which affected a country with no previous equine influenza exposure — demonstrated how devastating population-level disease can be in the absence of vaccinal immunity. Biosecurity practices that prevent or contain outbreaks are collective welfare interventions that protect not just the implementing yard but surrounding populations of horses.