HPAI and Dairy Cattle: What Producers Need to Know

What Is HPAI?

HPAI stands for highly pathogenic avian influenza. The specific strain affecting U.S. dairy cattle is H5N1, clade 2.3.4.4b — a variant that has circulated globally in wild bird populations for years and has caused devastating outbreaks in poultry flocks worldwide.

In March 2024, USDA confirmed the first cases of HPAI in U.S. dairy cattle, initially in herds in Texas and Kansas. This was unprecedented. Prior to 2024, HPAI was not known to cause clinical disease in cattle. The discovery that the virus could infect dairy cows, replicate in mammary tissue, and be shed at high concentrations in milk was a paradigm shift in our understanding of influenza biology.

Within months of the initial detections, HPAI was confirmed in dairy herds across multiple states. The outbreak exposed significant gaps in the U.S. livestock traceability infrastructure and led directly to accelerated enforcement of federal identification and movement requirements.

It is important to understand that HPAI in dairy cattle is not the same disease as HPAI in poultry. In poultry, HPAI causes extremely high mortality — often 90-100% of a flock within days. In dairy cattle, the disease presentation is markedly different: most affected cows recover, mortality is low, and the primary clinical impact is on milk production.

How HPAI Affects Dairy Cattle

HPAI in dairy cattle presents differently than in poultry. The virus shows a strong tropism for mammary gland tissue, meaning it preferentially infects the udder. This is why lactating dairy cattle are disproportionately affected compared to dry cows, heifers, or beef cattle.

Clinical Signs

• Sudden drop in milk production — typically 30-50% or more, occurring over 1-2 days. Some cows may nearly cease production.
• Abnormal milk appearance — milk becomes thick, yellow, and colostrum-like in consistency. It may appear curdled or contain flecks.
• Reduced feed intake — affected cows go off feed, sometimes dramatically.
• Lethargy — cows appear dull, sluggish, and less responsive than normal.
• Fever — elevated rectal temperature, though not always dramatic.
• Dehydration — secondary to reduced water and feed intake.
• Soft or loose manure — observed in some affected animals.

Recovery and Prognosis

Most dairy cattle recover from HPAI within approximately 2-3 weeks. Mortality is low — a notable contrast to the near-total mortality seen in poultry. However, some cows may not fully return to pre-infection milk production levels for the remainder of their lactation. The economic impact comes primarily from lost milk revenue during the illness period and the potential for permanent production decreases in some animals.

How It Spreads

The virus is shed primarily in milk. Milking equipment, milking parlors, and the milking process itself are considered major routes of within-herd transmission. Wild birds are believed to be the source of initial farm introductions. Contaminated equipment, vehicles, boots, and clothing may also play a role in between-farm transmission. The role of aerosol transmission between cattle remains under investigation.

The Federal Response

The confirmation of HPAI in dairy cattle triggered a rapid federal response. USDA APHIS issued a series of Federal Orders beginning with DA-2024-10 that imposed new requirements on the dairy industry.

Key Federal Actions

• Pre-movement testing mandate — lactating dairy cattle must test negative for influenza A virus before moving interstate.
• Bulk tank milk surveillance — USDA established a national milk testing surveillance program to detect HPAI in dairy herds through routine bulk tank sampling.
• Movement restrictions from positive premises — herds with confirmed HPAI face movement restrictions until testing demonstrates the herd is no longer shedding virus.
• Indemnity for affected herds — USDA established financial assistance programs for producers whose herds were confirmed positive, covering portions of lost milk revenue and testing costs.
• Mandatory reporting — HPAI is a reportable disease. Any suspected case must be reported to state and federal animal health officials immediately.

Evolving Requirements

The federal requirements around HPAI have changed multiple times since the initial Federal Order in April 2024. Testing protocols, the scope of covered animals, surveillance methods, and indemnity terms have all been updated as the situation evolved. Producers should not rely on any single source for current requirements — instead, verify the latest Federal Orders directly with USDA APHIS or their state veterinarian before every interstate movement of lactating dairy cattle.

Pre-Movement Testing Requirements

Under USDA APHIS Federal Orders, pre-movement testing is required for lactating dairy cattle moving interstate. The testing framework has been updated multiple times, so the information below describes the general structure — always verify current specifics before movement.

What Is Tested

Testing targets influenza A virus (not specifically H5N1) using RT-qPCR (real-time reverse transcription polymerase chain reaction). Samples may include individual milk samples or nasal swabs. Bulk tank milk testing may also be used as part of herd-level surveillance.

Who Performs Testing

Samples must be collected by or under the supervision of a USDA-accredited veterinarian or authorized state or federal animal health official. Testing is performed at USDA-approved laboratories, including the National Veterinary Services Laboratories (NVSL) and approved state and university diagnostic laboratories.

Validity Period

Test results have a limited validity window. The specific validity period has varied under different Federal Order updates. Producers should confirm the current validity period with their veterinarian or state animal health official before scheduling testing relative to their planned movement date.

Which Animals Are Covered

The pre-movement testing requirement applies to lactating dairy cattle moving interstate. Non-lactating dairy cattle (dry cows, heifers, calves, bulls) have generally been subject to different or reduced requirements, but this has varied over time. Beef cattle are not currently covered under the same testing framework.

How HPAI Accelerated the 840 RFID Mandate

The HPAI outbreak in dairy cattle exposed a critical weakness in the U.S. livestock traceability system: the inability to rapidly trace animal movements from affected herds.

When HPAI was confirmed in the first dairy herds, federal and state animal health officials needed to determine which animals had moved off those premises in the weeks and months before detection, and where those animals had gone. In many cases, this traceback was difficult, slow, or impossible because:

• Many dairy cattle were identified only by farm-level management numbers (barn numbers) that are not unique beyond the farm.
• Paper CVIs with handwritten descriptions made it difficult to link specific animals to specific movements.
• Visual-only ear tags (without RFID) could not be reliably matched to records after the fact.
• The fragmentation of identification systems across farms, breed registries, and state databases meant there was no single, reliable way to say “this cow was here, then moved there.”

This traceability gap directly contributed to USDA's decision to accelerate enforcement of the 840 RFID requirement under the Animal Disease Traceability (ADT) framework. The 840 RFID tag provides a unique, electronically readable, nationally standardized identifier that can be linked to movement records, CVI data, and health status information.

In short: HPAI demonstrated that the U.S. dairy industry could not trace cattle movements fast enough to contain a disease outbreak. The 840 RFID mandate is the federal government's primary response to closing that gap.

Biosecurity

Preventing HPAI introduction requires rigorous on-farm biosecurity. The virus can be introduced by wild birds, contaminated equipment, vehicles, clothing, or through the movement of infected animals onto the premises.

Farm Access Controls

• Restrict farm visitors — limit access to essential personnel only. Maintain a visitor log.
• Boot covers and dedicated footwear — provide disposable boot covers or require dedicated farm boots for anyone entering animal areas.
• Vehicle disinfection — require trucks and trailers to be cleaned and disinfected before entering the premises, particularly milk trucks and livestock haulers that visit multiple farms.
• Separate equipment — do not share milking equipment, hoses, or supplies between farms. If equipment must be shared, clean and disinfect thoroughly between uses.

Wild Bird Mitigation

• Minimize wild bird contact — reduce bird access to feed bunks, water sources, and loafing areas. Net or cover feed storage where practical.
• Remove standing water — puddles and standing water near cattle areas attract wild waterfowl, which are the primary reservoir for avian influenza.
• Monitor for dead birds — unusual numbers of dead wild birds on or near the farm should be reported to state wildlife agencies and may indicate local HPAI circulation.

Worker Safety

HPAI is a zoonotic disease — it can infect humans. While confirmed human cases associated with dairy cattle HPAI have been rare and mostly mild (primarily conjunctivitis), the potential for more serious illness exists. Workers who have direct contact with infected cattle, their milk, or contaminated environments should use appropriate personal protective equipment (PPE) including gloves, eye protection, and N95 respirators. Workers should be trained on proper PPE use and removal.

Monitoring and Reporting

Monitor your herd daily for clinical signs: sudden milk production drops, changes in milk appearance, off-feed cows, or lethargy. If you observe these signs — particularly a sudden, unexplained drop in production across multiple cows — report it to your veterinarian and state animal health officials immediately. Early detection and reporting are critical for controlling spread.

What To Do If You Suspect HPAI

If you observe clinical signs consistent with HPAI in your dairy herd — particularly a sudden drop in milk production across multiple cows with abnormal milk appearance — take the following steps immediately:

Impact on Interstate Movement

HPAI has added a significant layer of complexity to interstate dairy cattle movement. The pre-movement influenza A testing requirement is in addition to — not a replacement for — existing interstate movement requirements such as CVIs, TB testing, brucellosis testing, 840 RFID identification, and state-specific import permits.

Additional Testing Layer

For lactating dairy cattle moving interstate, producers now need to coordinate HPAI testing timing alongside any other required disease testing. This means more lead time, more veterinary visits (or combined visits), and more lab turnaround time to manage before the movement date.

State-Level Additions

Some states have imposed their own HPAI-related entry requirements beyond the federal baseline. These may include additional testing for cattle originating from states with confirmed HPAI cases, shortened CVI validity periods from affected areas, or enhanced reporting requirements. These state-level requirements vary and change frequently.

Movement from Positive Premises

Herds with confirmed HPAI face movement restrictions that go beyond pre-movement testing. Animals from positive premises may be prohibited from interstate movement until the herd has met specific testing and surveillance milestones demonstrating that viral shedding has ceased. The specific release criteria are determined by USDA APHIS and the state veterinarian.

Practical Advice

Before every interstate movement of lactating dairy cattle, check the current USDA APHIS Federal Orders and contact the destination state veterinarian's office to confirm current entry requirements. Do not assume that last month's requirements still apply. Build extra lead time into your movement planning to accommodate HPAI testing turnaround and any additional state-specific requirements.

Frequently Asked Questions

References

• USDA APHIS — HPAI Detections in Livestock
• USDA APHIS — Federal Orders on HPAI in Dairy Cattle
• FDA — Updates on HPAI and Food Safety
• CDC — Bird Flu (Avian Influenza)
• State veterinarian offices — contact your state veterinarian for current state-specific HPAI requirements and entry conditions

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