I haven't posted on this topic in a while because it seems like the situation changes almost daily. But here is the latest. This month, a new genotype of H5N1 was detected in dairy cattle in Nevada and Arizona. This new strain, genotype D1.1, originated from wild migratory birds. So, this new strain will need to be tested before moving forward.  

By way of background and update, in December 2024, USDA's Animal and Plant Health Inspection Service (APHIS) released its Federal Order requiring additional testing for Highly Pathogenic Avian Influenza (HPAI) requiring mandatory testing and reporting of raw (unpasteurized) milk, citing the Animal Health Protection Act (AHPA) and specifically sections 7 U.S.C. 8301-8315. This order was built on the prior order issued in April that required testing and reporting for H5N1 in dairy cattle. 

Coincident with the order, USDA rolled out its five-stage National Milk Testing Strategy. As of this posting and according to USDA, 42 of the lower 48 states have enrolled in the program via cooperative agreements, with Wisconsin, Illinois, North Dakota, Idaho, and Florida remaining. It is notable that Wisconsin, Idaho, and Florida all are significant dairy-producing states.

The five-stage plan begins with raw milk testing from milk silos at processing plants and then telescopes down to farm-level bulk tanks and then enhanced biosecurity and contact tracing/controls are implemented at affected farms. The off-ramp for affected farms is gained through continued negative bulk tank testing following eradication. USDA reports that California, Texas, Nevada, and Michigan all have confirmed affected herds, the vast majority of which have occurred in California; Pennsylvania, Mississippi, and Colorado are confirmed unaffected. Of course, the number of herds in each state varies widely.  

In my home state of Wisconsin, the second largest milk-producing state in the Union, it was announced this week that as of February 17th, no Wisconsin dairy herd has tested positive for H5N1. Once a cooperative agreement is reached with USDA and Wisconsin, raw milk testing will begin in Stage 2 (i.e., from the bulk tank at the farm level) - no raw milk testing from milk processor silos will occur. Importantly, farms shouldn't notice anything different as testing will occur by directing a portion of the normal milk sample to the State Lab for H5N1 testing. If a positive test is found, the Wisconsin Department of Agriculture will contact the farms directly as to the next steps.  

Importantly and worth repeating, the dairy food product supply chain that results from pasteurized milk remains safe.