In early 2024, dairy farmers in Texas were the first to notice something was wrong: cows were off their feed, their milk appeared thick and discolored, and overall production had dropped. The diagnosis came quickly-H5N1 avian influenza, a virus long associated with birds, had jumped into dairy cattle.

This development stunned the livestock industry. Until then, bird flu had largely been the concern of poultry producers. Avian influenza, particularly the highly pathogenic H5N1 strain, had circulated in wild birds and poultry flocks since its detection in the U.S. in late 2021. But its leap into cows was unprecedented-and it exposed vulnerabilities in an industry unprepared for a zoonotic spillover.

Within weeks, veterinarians and diagnostics labs confirmed the virus in samples from multiple states. As of mid-2025, over 1,000 dairy herds in 17 states have reported infections. The virus seems to spread cow-to-cow, aided by the frequent interstate movement of dairy animals-routine within the U.S. supply chain but largely invisible to the public.

Unlike poultry farmers, who adopted aggressive biosecurity measures after losing over 50 million birds to bird flu in 2015, dairy producers had no such blueprint. With little experience combating this type of pathogen, the industry had to move fast. Herds were monitored using wearable collars that track feeding and rumination patterns. When data showed abrupt declines in food intake and cud-chewing, it became clear that something more than routine illness was unfolding.

Fortunately, pasteurization has proven effective in deactivating H5N1 in milk, making commercial dairy products safe. But in raw milk or in milking equipment, the virus has shown signs of lingeriraising questions about how it spreads within herds and to other animals on the farm. Notably, some cats on affected farms have died after drinking infected raw milk.

The Centers for Disease Control and Prevention (CDC) has reported more than 70 confirmed human cases of H5N1 in the U.S. since the dairy outbreak began, mostly among farmworkers. These cases have been mild so far, but the sustained presence of the virus in mammals is a red flag for public health. Virologists warn that continued circulation in cows could increase the risk of mutations that enable human-to-human transmission.

In response, the USDA and state agencies have ramped up surveillance, testing bulk milk samples using PCR methods and supporting genomic sequencing to track viral evolution. Laboratories like Cornell University's Animal Health Diagnostic Center are central to this effort, processing hundreds of samples daily to identify new cases and mutations.

For many dairy farmers, the crisis has prompted a broader rethinking of livestock health protocols and the gaps in disease preparedness. Unlike poultry, dairy cows are lolived and central to farm operations. Their illness affects not only milk output but also the viability of entire supply chains.

The implications are far-reaching. Lawmakers drafting the next Farm Bill are likely to face pressure to include stronger support for dairy biosecurity, funding for animal disease research, and perhaps compensation mechanisms for losses due to outbreaks like H5N1. Meanwhile, veterinary experts and public health officials stress the need for cross-species disease monitoring-especially as climate change and global trade increase the risk of future zoonotic events.

The outbreak has exposed how interconnected the U.S. livestock industries are-and how a pathogen once confined to birds can rapidly reshape the priorities of an entire sector. Whether H5N1 becomes a persistent threat or a wake-up call that spurs lasting reform will depend on how quickly the dairy industry, policymakers, and scientists act.