Evaluation of nebulised hay dust suspensions (HDS) for the diagnosis and investigation of heaves. 2: Effects of inhaled HDS on control and heaves horses.
Authors: Pirie R S, Collie D D S, Dixon P M, McGorum B C
Journal: Equine veterinary journal
Summary
# Editorial Summary: Nebulised Hay Dust Suspensions for Heaves Diagnosis Researchers evaluated whether inhaled hay dust suspensions (HDS) could reliably distinguish between horses with heaves and healthy controls by measuring airway inflammatory responses and lung function in six unaffected and seven asymptomatic heaves-affected horses. Challenge with HDS provoked the classic heaves phenotype in affected animals—marked neutrophilic airway inflammation, obstructive dysfunction, and excessive mucus production—whilst controls mounted only a mild neutrophil response at substantially higher dust doses, with no overlap between the two groups' bronchoalveolar lavage fluid (BALF) neutrophil ratios. Notably, neither functional airway obstruction nor mucus hypersecretion occurred in control horses despite HDS exposure, and airway neutrophilia followed a dose-dependent gradient rather than an all-or-nothing pattern in both groups. For practitioners managing respiratory disease, these findings suggest HDS challenges represent a valuable diagnostic tool capable of definitively separating heaves-affected animals from clinically normal horses, potentially improving early identification and enabling more targeted investigation of subclinical airway inflammation in at-risk populations.
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Practical Takeaways
- •HDS inhalation challenge can be used as a diagnostic tool to differentiate horses with subclinical heaves from healthy controls
- •The test is sensitive enough to detect heaves in asymptomatic horses before clinical signs develop, useful for early identification
- •Response patterns are dose-dependent, allowing investigation of airway reactivity severity rather than simple yes/no diagnosis
Key Findings
- •HDS challenge differentiated control horses from heaves horses based on absence of airway dysfunction and mucus hypersecretion in controls despite mild neutrophilia
- •Heaves horses showed characteristic response to HDS including airway neutrophilia, obstructive dysfunction, and mucus hypersecretion
- •Airway neutrophilia response was dose-dependent in both groups rather than all-or-nothing
- •No overlap existed in BALF neutrophil ratios between control and heaves horses, suggesting potential diagnostic utility