Lower Airway Inflammation: What the Research Says
Evidence from 21 peer-reviewed studies
What Professionals Should Know
- •For horses with equine asthma or recurrent airway inflammation, consider switching from wood shavings to peat bedding to reduce lower airway neutrophilic response
- •Bedding material selection has measurable effects on airway inflammation markers even in healthy horses; this effect will likely be more pronounced in asthmatic individuals
- •Respiratory rate and visible mucus scores may not be sensitive indicators of bedding-related airway inflammation—cytological examination provides more definitive assessment
- •For horses with equine asthma or respiratory sensitivity, baled peat bedding is superior to straw pellets and loosely stored peat in reducing airway inflammation
- •Wood pellet bedding performs similarly to baled peat and may be a practical alternative if peat availability or cost is a concern
- •Storage and packaging matter: keep peat bales plastic-covered rather than loose to minimize dust and inflammatory triggers in the stable environment
- •Nebulized dexamethasone reduces microbial diversity in asthmatic horses but may increase opportunistic fungal pathogens like Alternaria; monitor respiratory health after treatment
- •Dexamethasone treatment alters herpesvirus gene expression (increased EHV-2, decreased EHV-5); consider implications for latent viral reactivation in treated horses
- •Environmental management (reducing dust exposure) may be as important as or more important than corticosteroid treatment in controlling respiratory microbiota changes in asthmatic horses
- •Respirable silica exposure should be considered as a potential risk factor for equine asthma; evaluate stable management practices and forage quality to minimize dust and mineral particle inhalation
- •Horses with persistent or worsening asthma despite standard management may benefit from environmental assessment focusing on dust control, improved ventilation, and reduced bedding/hay mineral content
- •Bronchoalveolar lavage with spectrometry analysis can identify silica burden in asthmatic horses and may help guide targeted environmental modifications
- •Heart rate variability analysis during treadmill exercise testing can help identify cardiac arrhythmias and lameness in Thoroughbreds presenting with poor performance
- •Lower HRV during submaximal exercise may indicate lameness, while higher HRV across all phases may signal underlying arrhythmias requiring further investigation
- •Treadmill exercise testing with HRV analysis provides objective data to differentiate between cardiac and musculoskeletal causes of poor performance in racehorses
- •Horses with summer pasture-associated asthma show distinct allergic inflammation patterns; diagnosis and management should focus on allergen avoidance and anti-inflammatory strategies rather than antimicrobial approaches
- •The elevation of IL-5 and other Th2 cytokines suggests that affected horses may benefit from targeted therapeutic interventions aimed at modulating allergic responses
- •Clinicians should recognize that pasture-associated asthma in tropical environments represents a chronic allergic condition requiring environmental and management modifications for long-term control
- •Standardbreds presenting with poor race performance should be evaluated for lower airway inflammation via BAL cytology, as neutrophilic inflammation directly impairs fitness parameters and lactate clearance
- •Different MEA subtypes (neutrophilic vs. eosinophilic-mastocytic) show distinct effects on performance metrics; treatment protocols may need to be tailored based on BAL cell populations
- •Fitness testing (incremental treadmill test with lactate and heart rate monitoring) can help identify airway inflammation-related performance limitations in racehorses
- •Cytokine profiling (particularly TNF-α, CXCL-8, and IFN-γ levels) may help differentiate severe asthma from milder disease and guide targeted anti-inflammatory therapy selection
- •Current clinical classification of equine asthma into mild-to-moderate versus severe categories is supported by distinct inflammatory endotypes, but further phenotypic subdivision may improve diagnostic and treatment precision
- •Future therapeutic development should focus on modulating elevated neutrophilic and lymphocytic airway inflammation in severe asthma rather than targeting mast cell proteases
- •Monitor horses with respiratory sensitivity during high air pollution days; respiratory signs may appear 2-3 weeks after pollution exposure peaks
- •Use local Air Quality Health Index (AQHI) data to anticipate increased airway inflammation risk and adjust training/outdoor exposure accordingly for susceptible horses
- •Consider environmental air quality as a modifiable risk factor in managing horses with inflammatory airway disease alongside traditional management strategies
- •Horses presenting with poor racing performance and mild-moderate signs of airway disease should be evaluated with BALF cytology, as neutrophil-dominated inflammation directly correlates with reduced aerobic capacity
- •The degree of neutrophil infiltration in BALF provides a quantifiable predictor of athletic capacity loss—higher neutrophil counts indicate greater performance compromise
- •Management strategies targeting airway inflammation reduction may improve racing performance in affected young Standardbreds by restoring blood-gas exchange efficiency
- •Full-time pasture turnout does not eliminate mild/moderate airway inflammation in horses; expect that ~60-87% of pastured adults will have some degree of lower airway disease detectable on BAL
- •Respiratory status changes seasonally in pastured horses, so clinical assessment and treatment decisions may need seasonal adjustment rather than assuming one-time year-round management solves respiratory issues
- •Round-bale hay storage and feeding methods may contribute to airway inflammation in pastured horses; evaluate forage quality and hay management as part of EAS management even for full-time pastured horses
- •EBC pH and H2O2 levels may be useful noninvasive diagnostic tools for detecting lower airway inflammation when endoscopy or bronchoalveolar lavage is not immediately available
- •Environmental conditions (temperature and humidity) during sample collection can significantly affect biomarker results, so standardization of collection procedures is important for reliable interpretation
- •This technique offers a potentially less invasive alternative to traditional airway sampling methods for monitoring airway disease progression and treatment response in individual horses
- •When you see degenerate neutrophils on tracheal wash cytology, especially in younger horses, culture and sensitivity testing is strongly indicated to guide targeted antimicrobial therapy
- •The absence of degenerate neutrophil changes may support non-infectious causes of airway inflammation, helping narrow your differential diagnosis
- •Age and season should be considered when interpreting tracheal wash cytology results, as younger horses and winter submissions show higher baseline degenerate neutrophil rates
- •Observe for bronchial collapse during BAL procedures in your horses—it is a reliable clinical indicator of lung inflammation and should prompt further diagnostic consideration
- •Expect reduced fluid recovery from BAL in horses with significant airway collapse, which may affect diagnostic yield and interpretation
- •Bronchial collapse during BAL suggests underlying airway inflammation; clinicians should correlate findings with clinical signs and consider anti-inflammatory management strategies
- •Adenosine signalling pathways represent a novel therapeutic target for modulating lower airway inflammation in horses with equine asthma or recurrent airway obstruction
- •Selective A(2A) adenosine receptor antagonists may enhance anti-inflammatory responses in airway-compromised horses and warrant further investigation as potential treatments
- •Future clinical trials should evaluate adenosine receptor ligands as adjunctive therapies for managing equine lower airway disease, particularly in cases with elevated neutrophilic inflammation
- •Serum SP-D measurement may offer a non-invasive biomarker for detecting and monitoring lower airway inflammation in clinical practice
- •SP-D could help differentiate pulmonary injury severity and guide treatment decisions for horses with respiratory disease
- •Further research is needed to establish reference ranges and clinical thresholds for SP-D in horses with naturally occurring airway disease
- •Use modified May-Grunwald Giemsa staining as the gold standard for donkey BALF analysis if accurate mast cell identification is clinically important for your diagnosis
- •If relying on Diff-Quick staining alone, be aware of potential mast cell miscounting and consider confirmation with alternative staining methods when mast cells are clinically significant
- •Results from this donkey study align with equine literature, suggesting similar staining considerations may apply across equid species
- •Alveolar and blood-derived macrophages behave differently during airway inflammation, which may explain variable severity and progression of lower airway disease between individual horses
- •Understanding these cellular immune differences could inform future therapeutic strategies targeting specific macrophage populations in severe equine asthma cases
- •Further in vivo research is needed to translate these laboratory findings into practical management approaches for horses with inflammatory airway disease
- •A herbal extract-based nutraceutical supplement may offer meaningful clinical benefit for racehorses with mild-moderate asthma when combined with environmental management
- •Antioxidant supplementation could be considered as an adjunctive therapy to environmental modifications in managing lower airway inflammation
- •Clinical signs and airway mucus accumulation can be objectively monitored through endoscopy and cytology to assess treatment response
- •Stall particulate levels vary significantly by season and time of day, suggesting yard management strategies (such as ventilation timing and bedding management) should be adjusted seasonally to minimise exposure to respiratory irritants
- •Higher winter concentrations highlight the need for improved ventilation and dust control during cold months when stalls are typically more closed to conserve heat
- •Baseline particulate data can inform individual yard assessments and help identify which facilities may need targeted environmental modifications to support equine respiratory health
- •Understand that IAD diagnosed on your yard using tracheal wash and endoscopy (trIAD) may differ from referral-based BAL diagnoses (brIAD), affecting how you interpret results and clinical significance
- •Be aware that current consensus definitions exclude many field diagnoses, meaning routine yard-based IAD identification needs further validation regarding its clinical relevance and aetiology
- •Focus on investigating individual components of airway inflammation rather than treating IAD as a single syndrome until clearer diagnostic and prognostic criteria are established
Key Research Findings
Wood shavings bedding resulted in significantly higher tracheal wash neutrophil percentage compared to peat (P = 0.040 and P = 0.0045)
Bronchoalveolar lavage fluid neutrophil percentage was significantly higher with wood shavings versus subsequent peat period (P < 0.001)
No differences were found in respiratory rate or tracheal mucus score between bedding types
Peat bedding caused less neutrophilic lower airway inflammation than wood shavings in healthy adult horses
Baled peat (Peat 2) produced significantly lower tracheal and bronchoalveolar neutrophil percentages compared to straw pellet bedding (TW: P=0.0003, BALF: P=0.005)
Straw pellet bedding resulted in higher tracheal mucus scores and respiratory rates compared to baled peat (P=0.014 and P=0.026 respectively)
Wood pellet bedding reduced respiratory rate compared to baled peat (P=0.004) with no difference in airway inflammation markers
Loosely stored peat (Peat 3) caused significantly higher BALF neutrophil percentages than baled peat (P=0.04), suggesting storage method affects air quality
Nebulized dexamethasone (15 mg q24h for 13 days) decreased respiratory microbial diversity and altered relative abundance of 8 genera in the upper respiratory tract
EHV-2 DNA levels increased while EHV-5 DNA levels decreased following dexamethasone treatment
Alternaria, an opportunistic pathogen and asthma risk factor, increased with dexamethasone treatment
Environmental factors (dusty conditions) had a dominant effect over treatment on mycobiota composition
Intracellular birefringent silica particles were significantly elevated in severely asthmatic horses (12 particles/30 hpf) compared to moderately affected (4 particles/30 hpf) and controls (4 particles/30 hpf; P=0.01 and P=0.02 respectively)
Silica concentration in BALF was 1758 particles/mL in severely asthmatic horses versus 867 particles/mL in moderately affected horses and 355 particles/mL in controls (P=0.009 and P=0.0003)
Silica load in BALF was associated with neutrophilic airway inflammation in both moderately and severely asthmatic horses
Evidence Base
Effects of Bedding Material on Equine Lower Airway Inflammation: A Crossover Study Comparing Peat and Wood Shavings.
Mönki Jenni, Saastamoinen Markku, Karikoski Ninja et al. (2021) — Frontiers in veterinary science
Effects of Bedding Material on Equine Lower Airway Inflammation: A Comparison of Two Peat Beddings, Wood Pellet, and Straw Pellet.
Mönki Jenni, Saastamoinen Markku, Karikoski Ninja et al. (2021) — Frontiers in veterinary science
Effects of nebulized dexamethasone on the respiratory microbiota and mycobiota and relative equine herpesvirus-1, 2, 4, 5 in an equine model of asthma.
Bond Stephanie L, Workentine Matthew, Hundt Jana et al. (2020) — Journal of veterinary internal medicine
Exposure to respirable silica contributes to lower airway inflammation in asthmatic horses.
Romolo Alessandra, Costa Giulia, Sica Beatrice et al. (2024) — Journal of veterinary internal medicine
Heart rate variability during high-speed treadmill exercise and recovery in Thoroughbred racehorses presented for poor performance.
Hammond Anna, Sage William, Hezzell Melanie et al. (2023) — Equine veterinary journal
Molecular and Cellular Evaluation of Horses With Summer Pasture Associated Asthma Syndrome.
Sad Eliene Porto, Hess Tanja M, Santos Huarrisson Azevedo et al. (2023) — Journal of equine veterinary science
Impact of Lower Airway Inflammation on Fitness Parameters in Standardbred Racehorses.
Lo Feudo Chiara Maria, Stucchi Luca, Conturba Bianca et al. (2022) — Animals : an open access journal from MDPI
Initial investigation of molecular phenotypes of airway mast cells and cytokine profiles in equine asthma.
Woodrow Jane S, Hines Melissa, Sommardahl Carla et al. (2022) — Frontiers in veterinary science
Brankston Gabrielle, Greer Amy L, Marshall Quinn et al. (2020) — Frontiers in veterinary science
The Relationship between Lung Inflammation and Aerobic Threshold in Standardbred Racehorses with Mild-Moderate Equine Asthma.
Stucchi Luca, Alberti Elena, Stancari Giovanni et al. (2020) — Animals : an open access journal from MDPI
Bronchoalveolar Lavage Cytology Characteristics and Seasonal Changes in a Herd of Pastured Teaching Horses.
Davis Kaori Uchiumi, Sheats Mary Katherine (2019) — Frontiers in veterinary science
du Preez S, Raidal S L, Doran G S et al. (2019) — Equine veterinary journal
Association of neutrophil morphology with bacterial isolates in equine tracheal wash samples.
Jocelyn N A, Wylie C E, Lean M et al. (2018) — Equine veterinary journal
Bronchial collapse during bronchoalveolar lavage in horses is an indicator of lung inflammation.
Koblinger K, Hecker K, Nicol J et al. (2014) — Equine veterinary journal
Enhanced IL-6 transcriptional response to adenosine receptor ligands in horses with lower airway inflammation.
Zhang L, Franchini M, Wehrli Eser M et al. (2012) — Equine veterinary journal
Serum concentration of surfactant protein D in horses with lower airway inflammation.
Richard E A, Pitel P-H, Christmann U et al. (2012) — Equine veterinary journal
Evaluation of bronchoalveolar lavage fluid from donkeys using four different cytological stains: A pilot study.
Vitale V, Bindi F, Briganti A et al. (2024) — Journal of equine veterinary science
Equine alveolar macrophages and monocyte-derived macrophages respond differently to an inflammatory stimulus.
Kang Heng, Lee Gary Kwok Cheong, Bienzle Dorothee et al. (2023) — PloS one
Effect of the Administration of a Nutraceutical Supplement in Racehorses with Lower Airway Inflammation.
Stucchi Luca, Lo Feudo Chiara Maria, Stancari Giovanni et al. (2022) — Animals : an open access journal from MDPI
Airborne particulate size and concentrations in five Thoroughbred training yards in Newmarket (UK).
Davison Joshua A, Wylie Claire E, McGladdery Charles E et al. (2019) — Veterinary journal (London, England : 1997)