# High immune responder cows have lower treatment risk and reduced milk loss during highly pathogenic avian influenza H5N1 outbreaks

## TL;DR

Cows genetically selected for stronger immune responses are less likely to need treatment and lose milk during avian flu outbreaks.

## Contribution

This study shows that genomic selection for immune response improves resilience and reduces economic losses during HPAI H5N1 outbreaks in dairy cattle.

## Key findings

- High Immunity+ GEBV cows were 24% less likely to require supportive treatment.
- High Immunity+ GEBV cows lost 134 kg less milk post-treatment than low Immunity+ cows.
- Genetic selection for immune response reduces production losses and strengthens economic resilience.

## Abstract

Summary: Highly pathogenic avian influenza (HPAI) H5N1 has recently spilled over into US dairy cattle, posing new risks to herd health and milk production. This study evaluated whether genetic selection for improved immune response using Immunity+ genomic estimated breeding values (GEBVs) enhances resilience during HPAI outbreaks. Cows with high Immunity+ GEBVs were 24% less likely to require supportive treatment compared with those with low Immunity+ GEBVs. Following treatment, high Immunity+ GEBV cows lost an average of 134 kg less milk than cows with low Immunity+ GEBVs. These findings demonstrate that genetic selection for immune response can reduce treatment needs, limit production losses, and strengthen economic resilience during infectious disease outbreaks.

Summary: Highly pathogenic avian influenza (HPAI) H5N1 has recently spilled over into US dairy cattle, posing new risks to herd health and milk production. This study evaluated whether genetic selection for improved immune response using Immunity+ genomic estimated breeding values (GEBVs) enhances resilience during HPAI outbreaks. Cows with high Immunity+ GEBVs were 24% less likely to require supportive treatment compared with those with low Immunity+ GEBVs. Following treatment, high Immunity+ GEBV cows lost an average of 134 kg less milk than cows with low Immunity+ GEBVs. These findings demonstrate that genetic selection for immune response can reduce treatment needs, limit production losses, and strengthen economic resilience during infectious disease outbreaks.

•Supportive treatment is 24% less likely in high versus low Immunity+ cows.•Post-treatment milk loss was 134 kg lower in high versus low Immunity+ cows.•Genomic selection for immune response supports herd health and economic resilience.

Supportive treatment is 24% less likely in high versus low Immunity+ cows.

Post-treatment milk loss was 134 kg lower in high versus low Immunity+ cows.

Genomic selection for immune response supports herd health and economic resilience.

The spillover of highly pathogenic avian influenza (HPAI) hemagglutinin type 5 and neuraminidase type 1 (H5N1) into dairy cattle marks the emergence of a new threat to herd health and production efficiency for North American dairy cattle. To address this challenge, this study evaluated whether genetic selection for improved immune response, using Immunity+ GEBVs, can increase resilience to HPAI H5N1 in commercial dairy herds. Treatment records (n = 15,386) and daily milk yield data (n = 650) were obtained from herd management software from 6 large commercial dairy herds in the United States with confirmed HPAI H5N1 outbreaks. The association between Immunity+ GEBV classes and the likelihood of requiring supportive treatment was assessed using binomial logistic regression, while linear models were used to assess the effects of Immunity+ GEBV class on the length of the milk fluctuation period following treatment and total milk loss during this period. Cows with high Immunity+ GEBVs were 24% less likely to require supportive treatment compared with those with low Immunity+ GEBVs (odds ratio = 0.76; 95% CI: 0.64 to 0.9). High immunity cows also experienced significantly lower milk loss (484.46 kg; 95% CI: 440.61 to 528.30 kg) during the post-treatment fluctuation period compared with low immunity cows (618.10 kg; 95% CI: 561.08 to 675.12 kg). Overall, these findings support the value of selecting for enhanced immune response to improve animal health, reduce production losses, and strengthen economic resilience during disease challenges.