In an effort to monitor Highly Pathogenic Avian Influenza H5N1 (HPAI H5N1) in milk and dairy herds, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) has begun its National Milk Testing Strategy (NMTS) with the issuance of a new Federal Order and accompanying guidance, requiring that raw (unpasteurized) milk samples nationwide be collected and shared with USDA for testing.

USDA first announced its intent to test bulk raw milk samples for HPAI H5N1 in October 2024, as part of its response to the ongoing outbreak affecting North American dairy herds. The newly released NMTS guidance will facilitate comprehensive HPAI H5N1 surveillance of the U.S. milk supply and dairy herds.

The NMTS is designed to increase USDA’s and its public health partners’ understanding of HPAI H5N1 spread in the U.S. through a structured, uniform, and mandatory testing system that will help swiftly identify which states, and which specific herds within them, are affected by the virus. This will support the rapid implementation of enhanced biosecurity measures to decrease the risk of transmission to other livestock, and will inform efforts to protect farmworkers to help lower their risk of exposure.

The new Federal Order makes three new requirements:

1. Mandatory sharing of raw milk samples, upon request, from any entity responsible for a dairy farm, bulk milk transporter, bulk milk transfer station, or dairy processing facility that sends or holds milk intended for pasteurization
2. Herd owners with positive cattle must provide epidemiological information that enables activities such as contact tracing and disease surveillance
3. Private laboratories and state veterinarians must report positive results to USDA that come from tests done on raw milk samples drawn as part of the NMTS.

The first round of silo testing under the Federal Order and the NMTS is scheduled to begin the week of December 16, 2024, although some states are already conducting testing that is compatible with the NMTS.

APHIS will work with each state in the contiguous U.S. to execute testing in a way that works for the state and that aligns with NMTS standards. Once a state begins testing under the NMTS, APHIS will place that state into one of five stages based on the HPAI H5N1 virus prevalence in that state. As states move to another stage, APHIS will have a stronger picture of the U.S.’ progress towards eliminating HPAI H5N1 at state, regional, and national levels. These stages include:

1. Mandatory USDA National Plant Silo Monitoring: USDA will immediately begin nationwide testing of milk silos at dairy processing facilities. This national sample will allow USDA to identify where the disease is present, monitor trends, and help states identify potentially affected herds.
2. Determining a state’s HPAI H5N1 dairy cattle status: Building on the results of silo monitoring, in collaboration with states, USDA will also uphold bulk tank sampling programs that will enable the agency to identify herds in the state that are affected with H5N1.
3. Detecting and responding to the virus in affected states: For states with H5N1 detections, APHIS will work quickly to identify specific cases and implement rapid response measures, including enhanced biosecurity using USDA’s existing incentives programs, movement controls, and contact tracing.
4. Demonstrating ongoing absence of the virus in dairy cattle in unaffected states: Once all dairy herds in a given state are considered to be unaffected, APHIS will continue regular sampling of farms’ bulk tanks to ensure the disease does not re-emerge. Bulk tank sampling frequency will progressively decline as the state demonstrates continual silo negativity (e.g., weekly, monthly, and quarterly, if continually negative). If a state becomes affected, USDA will re-engage detection and response activities, and the state will return to Stage 3.
5. Demonstrating freedom from HPAI H5N1 in U.S. dairy cattle: After all states move through Stage 4, APHIS will work with states to begin periodic sampling and testing to illustrate long-term absence from the national herd.

As of December 6, six states will be included in the first round of states brought into the program for testing: California, Colorado, Michigan, Mississippi, Oregon, and Pennsylvania. As states begin testing under the NMTS, and as they move through the five stages, their progress will be shared on the USDA HPAI in Livestock Testing webpage. While the majority of states will enter the NMTS at Stage 1, USDA anticipates states with ongoing testing may meet the testing requirements described in Stages 2–4.

The new Federal Order does not override or supersede USDA’s April 24 Federal Order, which still requires the mandatory testing of lactating dairy cows prior to interstate shipment and requires that all privately owned laboratories and state veterinarians report positive test results connected with those tests.

USDA will co-host information sessions for all state animal health officials and state dairy regulators on December 10 and 11 to provide more information about the National Plant Silo Monitoring and sampling procedures.