A new paper from a team of Cornell researchers shows that the highly pathogenic avian influenza (HPAI) strain named H5N1 virus causes severe mastitis and decreased milk production in dairy cows, a drop-off that may extend beyond the clinical outbreak period.
The work describes the impact of HPAI to production parameters and its cost to the dairy industry.
Economic losses due to decreased milk production, mortality and early removal from the herd were estimated at $950 per clinically affected cow for a total cost of approximately $737,500 for just the one herd the team studied. This did not include any ongoing herd dynamics or reproductive losses for this herd.
In a paper titled "The impact of highly pathogenic avian influenza H5N1 virus infection on dairy cows" published July 15 in the journal Nature Communications, the researchers found cows clinically infected with HPAI presented a significantly increased risk of death and of premature removal from a herd of 3,876 adult cows in Ohio.
The most remarkable finding was the long duration of diminished milk production in clinically affected cows, said co-author Diego Diel, professor of virology in the Department of Population Medicine and Diagnostic Sciences and director of the Virology Laboratory at the Animal Health Diagnostic Center (AHDC), all in the College of Veterinary Medicine (CVM).
He says pasteurization efficiently inactivates the virus, rendering the milk safe for human consumption, but that a diminution in milk production presents an enormous financial burden to the producers of affected farms, and if added up to all affected farms, it is causing major economic losses to the United States' 9.3 million cow dairy industry.
"This represents a shock to production costs if you are affected by an outbreak," said Matthew MacLachlan, co-author and assistant professor in the Department of Population Medicine and Diagnostic Sciences (CVM). "For a clinically diagnosed cow, we found an average of $950 in costs, which includes the milk you expect to lose over 60 days and the possible cost of removing them from dairy production. Even if they recover, that's going to cost a dairy farmer $367 on average in milk losses."
Outbreaks of avian flu in dairy herds won't necessarily raise the price of milk for consumers, MacLachlan said.
"A lot goes into milk prices," he said. "There's marketing, packaging, transportation and many other factors. But an outbreak, as our study shows, causes a substantial cost to dairy producers. Although there are some government support programs for dairy farmers, they aren't as generous as they are for poultry farmers."
The HPAI outbreak, which began in 2022, has cost the U.S. poultry industry approximately $1.4 billion.
"Our work on dairy cows intensified after March 2024, when we detected spillover of avian flu from wild birds to dairy cows. We were one of the three labs that detected the spillover simultaneously," Diel said.
Since then, Diel said, he and a group of researchers has been looking at the food safety aspects of the virus on dairy products and in assessing the susceptibility of different animal species.
In cows, mastitis is a condition usually marked by the inflammation of the udder tissue often caused by bacterial infections.
"Because it's mostly caused by bacteria, not viruses, no one knew what was happening," said Felipe Peña Mosca, postdoctoral researcher in CVM. He said that about 20% of the herd was clinically affected, and that for these cows, milk production never fully came back. Of the 777 cows affected, with clinical disease he said almost 40% (298) left the herd in the first 2 months following the outbreak, either because of death or because their diminished milk yield made them less profitable.
"The farm did its best to isolate the affected animals," Peña Mosca said. But the virus was still able to spread across cows rapidly in only 23 days.
"One key strategy is implementing biosecurity measures to minimize these outbreaks, and the next step is developing vaccines," said Peña Mosca, who was first author on the paper. Authors also included Elisha Frye, associate professor of practice in the Department of Population Medicine and Diagnostic Sciences (CVM), and Daryl Nydam, faculty director in the Department of Public & Ecosystem Health (CVM).
It's a thorny problem, Diel said, because ordinarily mastitis is prevented through increased disinfection. In this particular case, those practices used for disinfection - pre-milking teat cleaning with a germicidal solution that is then toweled off - could be introducing the virus to the next cow. Study results suggest an association between cumulative exposure to the milking process and the risk of clinical disease, meaning the introduction of the virus could be during the milking process itself.
And even the biosecurity measures that can keep laying hens and broilers safer from infection by wild migratory birds are less straightforward.
"These animals live in open pens where there are a lot of opportunities for exposure to wild birds," Diel said.
For a disease that is now widely considered endemic, rather than associated with a single outbreak, and caused by a virus that continues to evolve and spread, Diel said, its impact on the dairy industry merits more study.
