Effects of genetic and environmental factors on chronic lower airway disease in horses.
Authors: Ramseyer Alessandra, Gaillard Claude, Burger Dominik, Straub Reto, Jost Ursula, Boog Cornel, Marti Eliane, Gerber Vincent
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Chronic lower airway disease in horses results from both inherited susceptibility and environmental triggers, yet the relative contributions of specific factors to disease severity remain poorly characterised. Researchers investigating this question recruited 406 horses across four groups: offspring of two RAO-affected Warmblood stallions, maternal half-siblings of one affected sire, and unaffected controls, then used owner questionnaires to grade respiratory signs on a four-point scale (HOARSI) alongside detailed risk factor assessment. Direct offspring of affected sires showed substantially higher rates of moderate to severe disease (29.6% and 27.3% respectively) compared with controls and maternal half-siblings (9.1% and 6.2%), with paternal lineage emerging as the strongest predictor of clinical severity, followed by hay feeding and age. The practical implication for breeding decisions is clear: selection away from affected sires should be prioritised, whilst environmental modifications—particularly reduction of hay dust exposure—appear especially important for managing cough frequency in genetically predisposed animals, even though such modifications had negligible effect on mild clinical presentations.
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Practical Takeaways
- •Breeding decisions matter significantly—offspring of RAO-affected stallions have substantially higher risk of moderate to severe disease; genetic screening should inform breeding programmes
- •Hay feeding is a modifiable risk factor for worsening respiratory signs; alternative forage or dust-reduced hay may reduce disease severity in genetically predisposed horses
- •Younger horses may show more severe signs, so respiratory assessment should be age-adjusted when evaluating RAO-affected individuals for management and monitoring purposes
Key Findings
- •F1S1 and F1S2 offspring showed moderate to severe clinical signs (HOARSI 3-4) in 29.6% and 27.3% respectively, compared to 9.1% in controls and 6.2% in maternal half-siblings, indicating strong genetic predisposition (P < 0.001)
- •Sire, hay feeding, and age were associated with more severe clinical signs in decreasing order of strength, with marked effects on coughing frequency and nasal discharge
- •Mild clinical signs were not associated with sire or hay feeding, suggesting environmental and genetic factors primarily influence moderate to severe disease manifestation