USDA APHIS (the Animal and Plant Health Inspection Service, the USDA division responsible for livestock disease surveillance) ended mandatory pre-movement H5N1 testing for lactating dairy cattle travelling interstate from states without confirmed outbreaks, effective 1 May 2026. 1 The agency stated that its Dairy Herd Status Programme and National Milk Testing Strategy provide sufficient surveillance coverage. The policy took effect on the same day Idaho confirmed its first dairy herd infection , opening a structural gap at the moment the fastest-escalating state in the outbreak began its surge.
The practical effect of pre-movement testing was detection at the point of interstate transfer: infected cows from herds not yet showing clinical signs would test positive before they entered a new state's herd. Without that gate, detection depends on destination-state surveillance finding clinical signs after arrival. For B3.13, whose ISG-suppression mechanism delays the fever and respiratory symptoms that typically flag sick cattle, the window between arrival and detectable illness may be longer than the testing regime assumed.
The timing sits alongside the Emory aerosol study , which established that B3.13 is present in milking-parlour air before dairy cows display overt symptoms. Both findings describe a pathogen that outruns clinical-sign detection; the APHIS rollback removes the one screening point that operated independently of symptom presentation. APHIS has not indicated any trigger conditions that would reinstate mandatory testing.
