Bovine coronavirus (BCoV) continues to show up in cattle submitted for respiratory disease investigation, particularly in young calves and during the colder months. A five-year analysis of diagnostic submissions found that 15.3% tested positive for the virus, with detection varying by age and season but no significant long-term increase or decrease.
The study combined diagnostic testing data from 2020 through 2025 with pathogen co-detection analysis, whole-genome sequencing and lung tissue examination. Together, the findings offer veterinarians an updated look at respiratory BCoV in U.S. cattle, including how often it was detected alongside other pathogens and what researchers found in circulating viral strains.
Young Calves Had the Highest BCoV Detection Rates
Researchers analyzed 4,505 respiratory diagnostic samples submitted to the Iowa State University Veterinary Diagnostic Laboratory between January 2020 and November 2025. Of those, 693 tested positive for BCoV using quantitative reverse-transcription PCR.
Detection was highest in the youngest calves and declined with age:
- 0 to 40 days: 20%
- 41 to 140 days: 17%
- 141 to 240 days: 15%
- 241 days and older: 10%
The association between increasing age and lower odds of a positive BCoV result was statistically significant. The results show a clear age-related pattern among tested cattle, although they do not establish why younger animals were more likely to test positive.
Because the analysis relied on diagnostic submissions rather than population-based sampling, these percentages should not be interpreted as prevalence across the U.S. cattle population.
BCoV Detection Followed a Seasonal Pattern
BCoV detection peaked repeatedly in late fall and winter, then declined during summer. Despite these seasonal fluctuations, researchers found no significant overall increase or decrease in positivity from 2020 through November 2025. They also found no significant long-term trends when analyzing results by age group or production type.
Detection rates were similar across production types, with no statistically significant differences:
- Dairy cattle: 17.7%
- Cow-calf operations: 15.8%
- Other production types: 15.6%
- Feedlot cattle: 14.3%
The pattern suggests that BCoV remained a recurring finding in respiratory diagnostic submissions, rather than showing a sustained rise over the study period.
Co-Infections Add Complexity to Respiratory Disease
BCoV was frequently detected alongside other respiratory pathogens. Of the original samples, 3,995 had complete results for all eight pathogens included in the co-detection analysis.
Bacterial pathogens were particularly common. Mycoplasma bovis was detected in 57.5% of samples, followed by Histophilus somni (56.0%), Pasteurella multocida (51.0%) and Mannheimia haemolytica (37.0%). Among viral pathogens, bovine respiratory syncytial virus was most common (18.4%), followed by BCoV (15.3%), bovine viral diarrhea virus (10.3%) and bovine herpesvirus 1 (1.8%).
Researchers also identified statistical associations between several pathogen pairs. The strongest included bovine herpesvirus 1 and bovine viral diarrhea virus (odds ratio [OR] = 6.90), H. somni and M. bovis (OR = 4.25), and M. bovis and BVDV (OR = 4.52). Associations were also found between BVDV and bovine respiratory syncytial virus (OR = 2.84), and between BCoV and M. haemolytica (OR = 1.98).
In practical terms, detection of one pathogen was associated with higher odds of detecting its paired pathogen in the same diagnostic dataset. These associations do not establish that one organism caused or intensified another infection, but they highlight the range of pathogens present in respiratory cases.
Lung tissue examination provided additional evidence of BCoV involvement in respiratory disease. Histopathology and immunohistochemistry identified BCoV antigen in affected airway epithelium, alongside lesions including epithelial proliferation, damage and inflammation. Bacterial co-infections were also present, making it difficult to attribute all observed lesions to BCoV alone.
Sequencing Adds Insight Into Circulating Strains
Researchers sequenced four BCoV genomes from lung samples collected in 2024. All four isolates belonged to genotype GIIb and clustered with previously identified U.S. strains. The analysis also identified genetic variation across several viral proteins and possible recombination events.
For practicing veterinarians, these findings offer additional surveillance context, not a reason to change clinical recommendations. The study did not establish whether the genetic changes affect disease severity, tissue tropism, immune recognition or vaccine protection. The researchers also did not directly compare the isolates with vaccine strains.
The genomic findings should be interpreted with caution because sequencing was limited to four selected samples with high viral loads. Further research is needed to determine whether the observed variation has practical implications for diagnosis, prevention or control.
What the Findings Mean for Cattle Health
For veterinarians investigating respiratory disease, the study reinforces three useful observations: BCoV detection was highest in the youngest calves, followed a recurring seasonal pattern and frequently occurred alongside other respiratory pathogens.
The genomic analysis adds information about circulating strains, but questions remain about whether the identified genetic changes affect clinical outcomes or vaccine protection. Continued diagnostic surveillance and further research will be needed to answer those questions.
The key limitation is that these findings describe diagnostic submissions, not all U.S. cattle. The 15.3% positivity rate reflects the samples tested during the study, not the national prevalence of BCoV.
