The H5N1 bird flu virus—specifically the 2.3.4.4b strain—has been found in U.S. dairy cattle. This virus is shed in milk, creating a serious risk of spreading between animals and even to humans.
Now, scientists have discovered a powerful on-farm solution. A new pilot study shows that acidifying raw milk to a pH of 4.1 with citric acid can fully inactivate both low-pathogenic (H6N2) and high-pathogenic (H5N1) avian flu viruses in milk within 6 hours.
This method could help farms control the spread of the virus—without needing costly pasteurization equipment.
Why Pasteurization Isn’t Enough
Pasteurization works. High-temperature short-time (HTST) and low-temperature long-time (LTLT) methods both kill H5N1 in milk.
But many farms don’t use pasteurization—especially for waste milk. USDA data shows:
- Only 43.8% of large farms pasteurize waste milk.
- Just 3% of medium and 1% of small farms do the same.
That’s a problem. Infected waste milk can carry high levels of live virus. Without treatment, it becomes a risk to calves, handlers, and neighboring farms.
What the Study Found
Researchers ran multiple trials. They first tested citric acid against the H6N2 virus (a low-risk stand-in for H5N1). Then, they used the same method on milk from cows infected with real H5N1.
The results were clear:
- Acidifying milk to a pH of 4.1–4.2 killed both viruses after 6 hours.
- No live virus was found after that time.
- A pH of 4.4 was not reliable.
- The lactoperoxidase system (an enzyme-based treatment) did not work.
Acidified milk held a stable pH throughout the test—meaning the process is reliable once started.
Real-World Impact
This method is ideal for:
- Farms that feed waste milk to calves
- Situations without pasteurization equipment
- Rapid treatment before milk is handled or discarded
The process is inexpensive and easy. Citric acid is safe (FDA GRAS status) and already used on many farms for feeding calves.
Key Observations
- Fat-rich milk may improve inactivation. More trials are needed to confirm this.
- pH matters. Results were best at pH 4.1—higher pH showed weaker results.
- This is the first study to confirm complete H5N1 inactivation in naturally infected milk using acidification.
What This Means for the Industry
This simple acidification process could offer small and mid-sized farms a practical, effective biosecurity tool. It requires no heat, no power, and no special equipment.
Next steps should include:
- On-farm field trials
- Testing different milk compositions
- Evaluating taste and nutritional effects for calf feeding
Conclusion
Acidifying raw milk to pH 4.1 with citric acid completely inactivated the H5N1 virus within 6 hours. It’s a safe, low-cost method that could help control bird flu spread—especially in farms without pasteurization systems.
As new H5N1 outbreaks emerge, this method could become a vital biosecurity practice.
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Article derived from: In-laboratory inactivation of H5N1 in raw whole milk through milk acidification: Results from a pilot studyCrossley, Beate M. et al.Journal of Dairy Science, Volume 108, Issue 3, 2264 – 2275 https://www.journalofdairyscience.org/article/S0022-0302(25)00051-7/fulltext
