Relationship of horse owner assessed respiratory signs index to characteristics of recurrent airway obstruction in two Warmblood families
Authors: LAUMEN E., DOHERR M. G., GERBER V.
Journal: Equine Veterinary Journal
Summary
# Editorial Summary: HOARSI Validation in RAO-Affected Warmblood Families Owner-reported respiratory assessments have become essential tools for large-scale genetic studies of recurrent airway obstruction (RAO), yet their reliability against objective clinical findings had not been rigorously validated. Laumen and colleagues evaluated 71 offspring from two RAO-affected Warmblood stallions, assigning each horse a HOARSI (horse owner assessed respiratory signs index) grade between 1 and 4, then comparing these owner-reported scores against comprehensive lower airway diagnostics including endoscopic examination, blood gas analysis, cytological analysis of tracheobronchial secretions and bronchoalveolar lavage fluid, and methacholine challenge testing. Horses graded as HOARSI 3/4 during clinical exacerbation demonstrated all hallmark RAO characteristics—coughing, nasal discharge, abnormal lung sounds, significantly elevated neutrophils in both TBS and BALF, excessive mucus accumulation and airway hyperresponsiveness—whilst HOARSI 3/4 horses in remission showed only increased tracheal mucus and elevated TBS neutrophils. Notably, phenotypic expression of lung disease did not differ significantly between the two families, confirming consistent disease manifestation across different genetic backgrounds. For practitioners and researchers, these findings validate HOARSI as a reliable phenotyping tool for identifying genuinely RAO-affected horses in genetic studies, providing confidence that large-scale owner-based screening programmes can accurately differentiate affected individuals without requiring invasive diagnostics on entire populations.
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Practical Takeaways
- •Owner-reported respiratory signs using the HOARSI index (1-4 scale) are a reliable screening tool for identifying RAO-affected horses, validating the use of owner observations in clinical and breeding decisions
- •HOARSI grades need clinical context: horses with the same grade may show different objective findings depending on whether they are in exacerbation or remission, so clinical examination remains important for severity assessment
- •The HOARSI tool appears consistent across different family lines, making it a standardized phenotyping method suitable for genetic studies and multi-barn comparisons of RAO prevalence
Key Findings
- •HOARSI grades 3/4 during clinical exacerbation showed characteristic RAO signs including elevated neutrophils in tracheobronchial secretions and bronchoalveolar lavage fluid, excessive mucus, and airway hyperresponsiveness to methacholine
- •HOARSI grades 3/4 horses in remission exhibited only increased tracheal mucus and elevated neutrophil percentages in tracheobronchial secretions without other RAO characteristics
- •HOARSI reliably identified RAO-affected horses and showed no significant phenotypic differences between the two Warmblood families studied
- •Owner-reported respiratory signs index (HOARSI) correlated well with objective lower respiratory tract examination findings including endoscopy, cytology, and airway reactivity testing