Grad Student Competition
Milk antibody presence and persistence against Highly Pathogenic Avian Influenza in dairy cows in Colorado
| Date/Time: |
8/28/2026
11:15
|
| Author: |
Rebecca Williamson |
| Clinic: |
Colorado State University |
| City, State, ZIP: |
Fort Collins, CO 80524 |
Rebecca Williamson, BS
1
;
Natalie Urie, DVM, MPH
1
;
Sami Smith , BS
1
;
Jason Lombard, DVM, MS
1
;
1Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, 80523, CO, USA
2AgNext, College of Agricultural Sciences, Colorado State University, Fort Collins, 80523, CO, USA
Introduction:
Highly Pathogenic Avian Influenza (HPAI) subtype H5N1 was identified in U.S. dairy cattle in March 2024 and has since emerged as a significant health concern, particularly in lactating cows exhibiting mastitis, decreased milk production, nasal discharge, and fever. Understanding antibody prevalence and persistence following natural infection is critical for informing surveillance and control strategies. The objective of this study was to quantify influenza A virus (IAV) antibody presence and persistence in milk at both the cow and herd level in HPAI-affected dairy herds.
Materials and methods:
Six HPAI-affected dairy farms in Colorado were voluntarily enrolled in a longitudinal study and underwent whole-herd quarterly milk sampling beginning 161 to 338 days after onset of clinical signs. Milk samples were collected from all lactating cows at each time point, representing a census of the lactating population. A total of 39,776 milk samples were collected between December 2024 and August 2025. Samples were tested for IAV antibodies using ELISA at Colorado State University or Iowa State University Veterinary Diagnostic Laboratories. Samples were classified as positive at a signal-to-noise (S/N) ratio <0.6. Apparent herd prevalence was calculated as the proportion of ELISA-positive samples per sampling event. Because a census sampling approach was used and farms were not randomly selected, results are descriptive and not intended for population-level inference.
Results:
Initial whole-herd ELISA testing demonstrated antibody-positive prevalence ranging from 16.3% to 46.2% across farms. Each farm completed two to three quarterly sampling events, allowing evaluation of antibody persistence over time. Patterns of antibody prevalence varied between herds. For example, Farms AO and AZ exhibited an initial decline followed by a rebound in antibody-positive cows (AO: 29.9% to 22.3% to 26.6%; AZ: 39.2% to 36.2% to 46.2%). Overall, results demonstrated heterogeneity in antibody persistence within and across herds more than one year following initial infection. Five of six herds declined in herd level prevalence of IAV antibodies from the first to second test. Interestingly, these five farms then had an increase in prevalence on the third quarterly test.
Significance:
These findings indicate that antibody presence in milk following natural HPAI infection is variable and may not confer consistent or sustained herd-level immunity. Continued surveillance and further investigation into immune dynamics are warranted to inform disease management strategies and support future vaccine development.
