Research on highly pathogenic avian influenza H5N1, a virus of growing concern following its spillover into dairy cattle,was featured at the 2025 Conference of Research Workers in Animal Diseases (CRWAD), held in Chicago from Jan. 18 to 21.
Several presentations focused on the virus's impact on livestock, its transmission dynamics, diagnostic advancements and potential control measures. For more information, you can access the proceedings here (Proceedings Archive – CRWAD).
Among the 12 presentations on this emerging issue at CRWAD was a study from UC Davis led by UC Cooperative Extension specialist Noelia Silva del Rio.
Silva del Rio's lab examined cow-related risk factors for clinical disease in 3,281 cows housed on a Colorado dairy farm that experienced a major HPAI H5N1 outbreak in May 2024. Most of the cows on this farm were pregnant and had been moved from a nearby location under the same ownership. The dairy manager chose to treat only severe cases; approximately 14% of cows received treatment for clinical signs of HPAI during the outbreak.
Clinical signs of disease risk varied by pen
In this operation, cows were housed in 12 different pens. Each pen housed between 176 and 345 cows; seven pens were free-stalls and five open-lots. While it is challenging to draw strong conclusions, due to the limited number of pens included in the study, the risk of receiving treatment for clinical disease ranged from 7% to 27% across pens. Six pens housed comparable cows (similar parity, pregnancy status, days after calving, and milk yield) and the risk of clinical signs of disease still ranged from 7% to 24%. These findings suggest that environmental and management factors should be further investigated to learn about disease spread and severity within a farm and pen.
Cows with multiple calves had higher disease risk
Cows that had calved more than once were almost twice as likely to develop clinical signs of HPAI H5N1 (18%) compared to first-lactation cows (9%).
Pregnancy increased clinical signs of disease risk
The researchers found that among mid- to late-lactation comparable cows (similar parity, days after calving, and milk yield), pregnancy increased the risk of clinical disease (18%) compared to non-pregnant cows (4%).
Further research
Outbreaks of HPAI may manifest differently across farms, so it is essential to investigate whether similar findings are observed in other locations. Expanding research to include more farms and diverse environments will provide valuable insights for developing effective prevention and control strategies.