Evaluation of nebulised hay dust suspensions (HDS) for the diagnosis and investigation of heaves. 3: Effect of fractionation of HDS.
Authors: Pirie R S, Dixon P M, McGorum B C
Journal: Equine veterinary journal
Summary
# Editorial Summary Heaves diagnosis relies on inhalation challenge testing, but uncertainty exists about whether the particulate or soluble components of hay dust are most important for triggering airway inflammation. Pirie and colleagues challenged seven heaves-affected horses and six healthy controls with whole hay dust suspension (HDS) and its fractionated components—separating soluble elements from fungal spores and particulates through centrifugation and repeated washing. Both groups showed airway neutrophilia (increased neutrophil recruitment) in response to HDS and soluble supernatant alone, but heaves horses mounted significantly greater inflammatory responses; critically, the soluble fraction alone provoked less inflammation than whole HDS despite comparable endotoxin and protease levels, whilst particulates alone induced only minimal response. The key finding was that combining soluble and particulate fractions recreated the full inflammatory response seen with whole HDS, demonstrating that both components contribute synergistically to airway inflammation in heaves. For practitioners, this work validates the use of whole HDS suspensions over aqueous (soluble-only) extracts in diagnostic challenges, as whole suspensions more accurately replicate the pathophysiological response and provide superior sensitivity for identifying heaves-affected individuals.
Read the full abstract on PubMed
Practical Takeaways
- •When diagnosing suspected heaves, use whole hay dust suspensions for inhalation challenges rather than aqueous extracts alone, as particulates are critical for detecting the disease response
- •Hay dust exposure in heaves-affected horses triggers neutrophilic airway inflammation through both particulate and soluble components working together, supporting management strategies that minimize dust inhalation
- •Understanding that fungal spores and particulates are key triggers helps explain why dust control through soaking hay or improved ventilation is effective in heaves management
Key Findings
- •Whole HDS induced significantly greater airway neutrophilia in heaves horses (n=7) compared to control horses (n=6)
- •Supernatant (SUP) alone produced less neutrophilic response than whole HDS despite comparable endotoxin and protease content
- •Combined challenge with SUP and washed particulates (WP) approached the magnitude of response seen with whole HDS, demonstrating dust particulates contribute to neutrophil recruitment
- •Inhalation challenge with whole HDS is more effective for heaves diagnosis than aqueous dust extracts containing only soluble components