Tracheobronchial mucus viscoelasticity during environmental challenge in horses with recurrent airway obstruction.
Authors: Gerber V, King M, Schneider D A, Robinson N E
Journal: Equine veterinary journal
Summary
# Editorial Summary Recurrent airway obstruction (RAO) in horses involves complex airway inflammation, but whether diseased horses produce inherently abnormal mucus remains unclear; Gerber and colleagues investigated whether mucus viscoelasticity differs between RAO-affected and healthy horses, and critically, whether environmental challenge (straw bedding and hay feeding) triggers rheological changes that might impair clearance. Using oscillatory rheometry, the researchers measured mucus elasticity and viscosity at multiple timepoints over 48 hours, calculating mucociliary clearability and cough clearability indices alongside bronchoalveolar lavage fluid cytology in eight RAO horses in remission and matched controls. At baseline and 6 hours post-challenge, mucus properties were indistinguishable between groups; however, by 24 hours, RAO horses exhibited significantly increased viscoelasticity (log G* rising from 2.49 to 3.05 dyn/cm²) accompanied by substantial reductions in both clearability indices, whilst control horses showed no rheological changes. Importantly, mucus solids content and inflammatory cell counts did not correlate with these rheological shifts, suggesting that altered viscoelasticity—rather than simply increased mucus production—may be the mechanistic driver of mucus stasis during RAO exacerbations. For practitioners, this implies that environmental management to minimise dust and allergen exposure is critical during exacerbation risk periods, as the sudden rheological deterioration in RAO-susceptible horses would substantially impair both ciliary and cough-mediated clearance regardless of mucus volume.
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Practical Takeaways
- •Environmental management is critical for RAO-affected horses—straw bedding and hay feeding trigger unfavorable changes in airway mucus consistency that impair clearance, so use low-dust alternatives and consider soaking hay
- •RAO horses in remission have normal mucus properties but develop problematic viscoelasticity during exacerbation, indicating the disease is triggered by environmental factors rather than inherent mucus abnormality
- •Monitor for small airway disease signs during environmental challenge periods, as increased mucus stasis may occur without obvious changes in inflammatory cell counts
Key Findings
- •Mucus viscoelasticity increased significantly in RAO-affected horses from 2.49 dyn/cm² at baseline to 3.05 dyn/cm² at 24 hours after environmental challenge, while healthy controls showed no change
- •Environmental challenge caused decreased mucociliary clearability index (MCI) and cough clearability index (CCI) in RAO horses only
- •Mucus rheology was similar between RAO and control horses at baseline and 6 hours, but diverged at 24 and 48 hours post-challenge
- •Changes in mucus viscoelasticity did not correlate with bronchoalveolar lavage fluid cytology, suggesting rheological changes are independent of inflammatory cell counts