Bird flu or highly pathogenic avian influenza (HPAI) H5N1 was a wildcard for the dairy industry in 2024, as the first diagnosis in dairy cattle happened in Texas in late March. At that time, industry organizations encouraged dairy producers to tighten their biosecurity protocols to reduce transmission and, hopefully, prevent their herds from becoming infected. State veterinarians and animal health officials placed infected farms under quarantine, and some issued mandatory bulk tank sampling and other testing.
As of Feb. 20, there have been a total of 973 cases in 17 states; 747 of those cases were in California.
In preparing our 2025 State of Dairy, Progressive Dairy interviewed state veterinarians and animal health officials in the five states with the most cases of bird flu on dairy farms – Texas, Idaho, Michigan, Colorado and California. Respondents included: Lewis R. ‘Bud’ Dinges, Texas state veterinarian, along with other Texas Animal Health Commission (TAHC) executive veterinarians; Scott Leibsle, Idaho state veterinarian; Tim Boring, director of the Michigan Department of Agriculture and Rural Development (MDARD); Maggie Baldwin, Colorado state veterinarian; and Annette Jones, California state veterinarian.
When was the first case of bird flu on a dairy in your state? How did the first dairy become infected?
DINGES/TAHC: Diagnostic samples from two Texas dairies were confirmed positive for HPAI on March 25, 2024. At this time, there is no federal or Texas epidemiological consensus on how the first dairies were infected.
LEIBSLE: The first confirmed case in Idaho was March 29, 2024, when a dairy became infected after receiving a shipment of lactating cattle from an affected dairy in Texas.
BORING: The first H5N1 case was announced in Michigan on March 29, 2024. The farm recently received cattle from an affected premises in Texas before that herd showed any sign of disease. When the cattle were moved from Texas to Michigan, the cattle were not symptomatic and did not appear ill.
BALDWIN: Colorado had its first confirmed positive detection of HPAI in dairy cattle on April 25, 2024.
JONES: California’s first case of bird flu on our dairies was confirmed on Aug. 30, 2024. The first California dairy became infected from an out-of-state infected dairy. The primary factor of viral spread is through movement of infected livestock. H5N1-infected cattle can be asymptomatic from several days to a couple of weeks, so when infected cattle that look healthy are moved due to normal business operations, non-infected cattle are exposed to the virus.
What was the guidance provided by the state veterinarian’s office to limit spread? Were there any state-specific restrictions on cattle movement and/or additional testing requirements?
DINGES/TAHC: While guidance to dairy producers has evolved as more is learned about HPAI in dairy cattle, the TAHC provided the following general guidance to dairy producers beginning April 16.
Humans, other animals, vehicles and other objects or materials that come in contact with milk, spilled milk, unpasteurized milk, etc. may spread the virus and precautions should be taken to avoid spread.
An increased emphasis for all producers to evaluate biosecurity risks and mitigate all types of disease introduction and spread is encouraged.
- Heighten biosecurity practices to keep disease off the farm and to prevent and control disease spread on the farm.
- Pay particular attention to mammary health with special attention to good milking practices, including equipment disinfection and milking sick cattle separately or last.
- Isolate newly added animals and sick animals, and monitor closely for signs of illness.
- Avoid housing multiple species of animals together, and limit domestic pets, wildlife and unnecessary animals’ access to farm areas.
- Limit cattle movement to only necessary transport focused on preventing movement of disease.
- Practice diligent disinfection and replace clothing or personal protective equipment after handling other animal species, especially birds, farm pets or wildlife, and before handling cattle, especially in the milking parlor.
TAHC action was in accordance and evolved with the science and federal guidance as the incident developed. TAHC implemented restricted and/or controlled movements of lactating dairy cattle from positive premises, and non-clinical cattle moving to harvest were required to be permitted.
Additionally, on July 25, TAHC issued the order: TAHC Requires Pre-Movement Testing for Exhibition Dairy Cattle: Lactating Dairy Cattle Required to Test Negative for Influenza A Virus Prior to Intrastate Movement to Fairs, Shows or Exhibitions. This order will remain in effect until 60 days after the last detection of H5N1 in cattle herds in the U.S. Prior to interstate movement, lactating dairy cattle are required to receive a negative PCR test for Influenza A virus at an approved NAHLN laboratory using a NAHLN-approved assay and in accordance with the federal order effective April 29.
JONES: All infected dairies are immediately placed under quarantine to prevent the movement of infected animals and contaminated materials, equipment and vehicles from leaving the property. If movement is required, our subject matter experts work with dairy producers to coordinate the movement in a biosecure manner.
The California Department of Food and Agriculture (CDFA) has also provided educational materials with regular updates on our website since the first detection of bird flu in our dairies. Current updates can be found on online. There is a section titled Livestock Guidance Handouts and Forms with additional educational materials on how to protect their herds and other dairies.
California’s bulk milk tank testing strategy has been able to detect the virus before clinical signs show. Additionally, when a dairy completely recovers from infection and is released from quarantine, these dairies are placed on a surveillance list for bi-monthly testing through creameries to maintain continued monitoring of the virus throughout California.
On Jan. 8, California also placed a ban on all dairy cattle exhibitions from shows and fairs to reduce the risk of viral spread.
BALDWIN: Positive dairies were placed under quarantine, which restricted the movement of lactating dairy cattle. Additionally, positive dairies were required to implement biosecurity practices to limit the spread of bird flu.
Starting in July, Colorado was the first state in the country to institute mandatory bulk milk tank testing for all commercial cow dairies (86 total) to monitor for the virus.
LEIBSLE: All dairies in Idaho were advised to enhance all aspects of their biosecurity protocols to limit the risk of spread of the virus off/on the farm, as well as isolating symptomatic cattle from asymptomatic cattle to limit animal-to-animal transmission.
Idaho dairies confirmed to have HPAI-positive cattle on their facilities were placed under quarantine. No lactating cattle on an affected dairy were permitted to leave the premises unless traveling directly to slaughter. All affected dairies remained under quarantine until two consecutive negative HPAI tests of bulk tank milk were received.
BORING: MDARD made HPAI a reportable disease nearly immediately. On May 1, the “Determination of Extraordinary Emergency, “HPAI Risk Reduction Response Order" was signed in response to the ongoing HPAI outbreak in Michigan. The emergency order requires the following measures to be taken:
All Michigan dairy farms, as well as poultry operations considered commercial by the USDA Animal & Plant Health Inspection Service (APHIS) must develop and implement biosecurity practices that include:
- Designation of a biosecurity manager.
- Designation of a line of separation to represent the perimeter of a secure area, limiting access points.
- Establishment of cleaning and disinfection practices and procedures at those access points for both vehicles and individuals. This must include deliveries of feed and other supplies, and training for employees.
- Establishment of a logbook maintaining a record of all vehicles and of individuals who have gotten out of vehicles and crossed those access points, to be retained and made available for examination upon request by MDARD.
- All lactating dairy cattle, and those in the last two months of pregnancy, are prohibited from being exhibited until there are no new cases of HPAI in dairy cattle in the state of Michigan for at least 60 consecutive days. No dairy cattle of any age from an infected premises may be exhibited until further notice.
Number of confirmed cases on dairy farms
(As of Feb. 20, 2025)*
California: 747 (Last confirmed case: Feb. 14, 2025)
Colorado: 64 (Last confirmed case: Aug. 13, 2024)
Idaho: 35 (Last confirmed case: Oct. 22, 2024)
Michigan: 31 (Last confirmed case: Jan. 21, 2025)
Texas: 27 (Last confirmed case: Dec. 13, 2024)
*Note: For total counts in other states, visit online.
