Equine Asthma: Diagnostic Sampling, Environmental Control, and Treatment Monitoring

At a Glance

Equine asthma encompasses a spectrum of inflammatory airway conditions ranging from mild-to-moderate disease (previously termed inflammatory airway disease) to severe asthma (previously termed recurrent airway obstruction or heaves). Diagnosis relies on airway sampling with cytologic interpretation, environmental modification to reduce inhaled dust and allergens, pharmacotherapy for acute control, and systematic monitoring of treatment response. The table below summarizes the key diagnostic and management approaches for the two primary clinical presentations.

Scope and Clinical Context

Equine asthma is a chronic inflammatory airway disease that affects horses of all ages and uses. The condition has been reclassified under a unified nomenclature to reflect the underlying inflammatory pathophysiology instead of historical labels based on clinical severity. The Merck Veterinary Manual provides foundational information on respiratory diseases in horses. The American College of Veterinary Internal Medicine (ACVIM) has published consensus statements on equine asthma diagnosis and management. The World Organisation for Animal Health (WOAH) addresses animal health and welfare standards relevant to respiratory disease management in horses.

Veterinarians must distinguish equine asthma from other causes of respiratory signs including exercise-induced pulmonary hemorrhage, bacterial pneumonia, viral respiratory infections, and parasitic lung disease. The diagnostic approach requires systematic airway sampling, cytologic interpretation, and correlation with clinical findings. Environmental control is the cornerstone of long-term management, and pharmacotherapy is used to control inflammation and relieve bronchospasm during exacerbations.

Diagnostic Sampling: Bronchoalveolar Lavage and Tracheal Wash

Indications for Airway Sampling

Airway sampling is indicated for any horse with persistent cough, poor performance, exercise intolerance, or abnormal respiratory effort that cannot be explained by other conditions. The decision to perform bronchoalveolar lavage (BAL) versus tracheal wash (TW) depends on the clinical question and the suspected location of airway inflammation. BAL is considered the gold standard for assessing lower airway inflammation because it samples the alveolar and small airway compartments. TW samples the larger airways and trachea and may not accurately reflect inflammation in the distal airways.

A 2024 review of equine asthma diagnostics discusses the factors that influence test interpretation and the difficulties in diagnosing subclinical disease. The authors note that BAL cytology is more sensitive than TW for detecting mild lower airway inflammation, particularly in performance horses that may not show obvious clinical signs at rest.

Bronchoalveolar Lavage Procedure

BAL is performed using a sterile catheter passed through the nasal passage into the trachea and wedged into a bronchus. The horse is sedated with an alpha-2 agonist and an opioid such as butorphanol. Sterile saline is instilled and immediately aspirated. The volume of fluid recovered should be at least 50% of the instilled volume for adequate cytologic evaluation. The sample is placed in EDTA tubes and processed within 2-4 hours for cell counts and differential cytology.

A 2019 case report describes a fatal pulmonary hemorrhage in a horse during BAL. The mare developed massive hemorrhage after a severe cough during catheter placement. Necropsy revealed a chronic lymphoplasmacytic inflammatory process in the left bronchi with severe perivascular fibrosis. This case underscores that BAL, while generally safe, carries rare but serious risks. Horses with preexisting airway inflammation may have fragile bronchial vessels that can rupture with coughing or catheter manipulation.

Tracheal Wash Procedure

TW is performed by passing a catheter through the nasal passage into the trachea, instilling sterile saline, and aspirating the fluid. The procedure is less invasive than BAL and may be preferred by owners and trainers. However, TW cytology does not reliably predict BAL cytology results. A 2025 study comparing TW and BAL cytology in racehorses with exercise-induced pulmonary hemorrhage found that TW could not be considered a reliable alternative to BAL for comprehensive characterization of lower airway inflammation. Reliance on TW alone could lead to incomplete or misleading clinical assessments.

Cytologic Interpretation

BAL cytology is interpreted based on total cell count, differential cell percentages, and the presence of mucus, hemosiderophages, or infectious agents. Normal BAL fluid contains predominantly macrophages with fewer lymphocytes, neutrophils, mast cells, and eosinophils. The threshold for abnormal neutrophil percentage varies by laboratory and clinical context. Racehorses with mild-to-moderate asthma may show neutrophil percentages of 5-10%, while horses with severe asthma often have neutrophil percentages exceeding 25%.

Mast cell and eosinophil percentages are also evaluated. Increased mast cells may be associated with mild-to-moderate asthma in young horses. Eosinophilia can indicate parasitic infection or hypersensitivity. The presence of hemosiderophages indicates prior pulmonary hemorrhage, which is common in racehorses and can complicate cytologic interpretation.

A 2017 publication on equine asthma diagnosis discusses approaches beyond BAL cytology, including pulmonary function testing, airway reactivity assessment, and biomarker analysis. These advanced techniques may be useful in cases where BAL cytology is equivocal or when monitoring response to therapy.

Limitations of Airway Sampling

BAL and TW have several limitations that veterinarians must consider. BAL samples only a single lung lobe, and inflammation may be patchy. A normal BAL does not rule out airway inflammation in other regions. TW samples the larger airways and may miss distal inflammation. Both procedures require sedation and carry risks of coughing, hemorrhage, and transient respiratory distress.

The timing of sampling relative to environmental exposure and treatment is important. Horses that have been removed from dusty environments for several days may show reduced airway inflammation on BAL. Horses receiving corticosteroids may have suppressed inflammatory cell counts. Repeat sampling after treatment is necessary to assess response.

Environmental Control: Reducing Dust and Allergen Exposure

Principles of Environmental Management

Environmental control is the most important intervention for managing equine asthma. The goal is to reduce the horse's exposure to inhaled dust, mold spores, endotoxins, and other airborne irritants that trigger airway inflammation. The Merck Veterinary Manual emphasizes that environmental modification is the foundation of treatment for recurrent airway obstruction.

The primary sources of respirable dust in horse housing include hay, straw bedding, barn dust, and outdoor particulate matter. Hay is the most significant source because it contains mold spores, plant particles, and endotoxins. Straw bedding also contributes dust, particularly if it is moldy or dusty. Barn ventilation affects the concentration of airborne particles.

Low-Dust Forage Strategies

Hay should be the first target of environmental modification. Soaking hay in water for 15-30 minutes before feeding reduces respirable dust particles by up to 90%. Steaming hay with commercial hay steamers is also effective and may preserve more nutrients than soaking. Haylage or silage can be used as an alternative to dry hay, provided it is properly fermented and free of mold.

Pasture turnout is the ideal environment for horses with asthma because outdoor air has lower concentrations of dust and mold spores. Horses that cannot be turned out full-time should have access to a well-ventilated paddock or run-in shed during the day.

Bedding and Barn Management

Bedding should be low-dust and mold-free. Options include wood shavings, paper products, or pelleted bedding. Straw should be avoided because it is dusty and may contain mold. Deep litter systems that accumulate manure and urine should be avoided because they generate ammonia and dust.

Barn ventilation is critical for reducing airborne particle concentrations. Natural ventilation through open windows, doors, and ridge vents is effective in many climates. Mechanical ventilation systems with fans and air inlets can improve air exchange in enclosed barns. Horses should not be housed in stalls with poor air circulation or high humidity.

Practical Implementation Steps

1. Assess the horse's current environment: Evaluate hay type and storage, bedding material, barn ventilation, and turnout schedule.
2. Implement immediate changes: Switch to soaked or steamed hay, change bedding to low-dust material, and increase turnout time.
3. Monitor clinical response: Observe cough frequency, respiratory effort, and nasal discharge over 2-4 weeks.
4. Adjust management based on response: If clinical signs persist, consider additional changes such as moving the horse to a different barn or using a dust-free stall.
5. Document environmental changes and clinical outcomes in the medical record.

Common Failure Patterns

Failure to achieve environmental control often results from incomplete or inconsistent implementation. Owners may soak hay for too short a time, use dusty bedding despite recommendations, or keep horses in poorly ventilated barns. Some horses require complete removal from the barn environment to achieve remission. Veterinarians should emphasize that environmental control is a continuous process, not a one-time intervention.

Pharmacotherapy: Corticosteroids and Bronchodilators

Indications for Pharmacotherapy

Pharmacotherapy is indicated for horses with moderate to severe clinical signs, horses that do not respond adequately to environmental control alone, and horses that require rapid relief of respiratory distress. The goal of pharmacotherapy is to reduce airway inflammation, relieve bronchospasm, and improve lung function. Treatment should be combined with environmental modification for optimal results.

Corticosteroids

Corticosteroids are the primary anti-inflammatory drugs used in equine asthma. They reduce airway inflammation by suppressing inflammatory cell activation and cytokine production. Inhaled corticosteroids are preferred for long-term management because they deliver drug directly to the airways with minimal systemic absorption. Fluticasone propionate is commonly used and is administered via a metered-dose inhaler with a spacer device.

Systemic corticosteroids are used for initial control of severe asthma or when inhaled therapy is not feasible. Dexamethasone and prednisolone are commonly used. Systemic corticosteroids carry risks of immunosuppression, laminitis, and adrenal suppression, particularly with prolonged use. The lowest effective dose should be used for the shortest duration necessary.

Bronchodilators

Bronchodilators are used to relieve bronchospasm and improve airflow. They are not anti-inflammatory and should not be used as sole therapy for asthma. Beta-2 agonists such as albuterol (salbutamol) are administered via inhalation and provide rapid bronchodilation within 5-15 minutes. They are useful for acute exacerbations and before exercise in horses with exercise-induced bronchospasm.

Anticholinergic bronchodilators such as ipratropium bromide are also available for inhalation. They have a slower onset but longer duration of action than beta-2 agonists. Combination therapy with corticosteroids and bronchodilators may be more effective than either drug alone.

Treatment Monitoring

Response to pharmacotherapy should be monitored clinically and with repeat airway sampling. Clinical parameters include cough frequency, respiratory rate and effort, nasal discharge, and exercise tolerance. Lung function testing with a portable spirometer or respiratory inductance plethysmography can provide objective measures of airway obstruction.

Repeat BAL cytology after 4-8 weeks of treatment is recommended to assess reduction in airway inflammation. A decrease in neutrophil percentage indicates a positive response. If cytology does not improve, the veterinarian should reassess environmental control, consider alternative or additional pharmacotherapy, and evaluate for other causes of airway inflammation.

Records and Measurements

Clinical Scoring Systems

A standardized clinical scoring system helps track disease severity and treatment response. The scoring system should include parameters such as cough frequency (none, occasional, frequent), respiratory rate at rest, nostril flare, heave line, and nasal discharge. Each parameter is scored on a scale of 0-3, and the total score is calculated. A decrease in score indicates improvement.

BAL Cytology Records

BAL cytology results should be recorded in a standardized format that includes total cell count, differential percentages (macrophages, neutrophils, lymphocytes, mast cells, eosinophils), and the presence of mucus, hemosiderophages, or infectious agents. The date of sampling, the horse's current environment, and any recent treatments should be noted. Serial cytology results allow the veterinarian to track changes over time.

Environmental Assessment Records

A written environmental assessment should document the type of hay and bedding, hay storage conditions, barn ventilation, turnout schedule, and any recent changes. The assessment should be updated whenever management changes are made. This record helps identify environmental triggers and evaluate the effectiveness of interventions.

Treatment Records

Treatment records should include the drug, dose, route, frequency, and duration of therapy. Any adverse effects or lack of response should be noted. The record should also include the date of treatment initiation, the date of any dose adjustments, and the date of treatment discontinuation.

Common Failure Patterns

Incomplete Environmental Control

The most common reason for treatment failure is incomplete environmental control. Owners may implement some changes but not others, or they may revert to previous management practices after initial improvement. Veterinarians should emphasize that environmental control is the foundation of treatment and must be maintained consistently.

Misdiagnosis

Equine asthma can be confused with other respiratory conditions such as exercise-induced pulmonary hemorrhage, bacterial pneumonia, or viral respiratory infections. BAL cytology is essential for accurate diagnosis. Horses with exercise-induced pulmonary hemorrhage may have hemosiderophages on BAL but may not have neutrophilic inflammation. Bacterial pneumonia requires culture and sensitivity testing for appropriate antibiotic selection.

Inadequate Pharmacotherapy

Inhaled corticosteroids may be underdosed or administered incorrectly. The spacer device must be properly assembled and the horse must be trained to accept the mask. Systemic corticosteroids may be tapered too quickly, leading to relapse. Bronchodilators may be overused without adequate anti-inflammatory therapy.

Concurrent Disease

Horses with equine asthma may have concurrent conditions such as pituitary pars intermedia dysfunction (PPID), which can worsen airway inflammation. Older horses with PPID may require additional management for metabolic disease. Horses with recurrent airway obstruction may develop secondary bacterial infections that require antibiotic therapy.

Welfare and Safety Context

Animal Welfare Considerations

Equine asthma causes significant respiratory distress, exercise intolerance, and reduced quality of life. Horses with severe asthma may have difficulty breathing at rest and may be unable to perform normal activities. The World Organisation for Animal Health (WOAH) emphasizes that animal health and welfare standards should include prevention and treatment of respiratory diseases.

Veterinarians have a responsibility to diagnose equine asthma accurately and implement effective treatment. Horses that do not respond to treatment should be evaluated for other conditions and may require referral to a specialist. Euthanasia should be considered for horses with severe, unresponsive asthma that causes significant suffering.

Safety Considerations for Veterinarians

Airway sampling procedures carry risks for both the horse and the veterinarian. Horses may cough, move suddenly, or become agitated during BAL or TW. Proper sedation and restraint are essential. The veterinarian should be prepared to manage complications such as hemorrhage, respiratory distress, or cardiac arrhythmias.

Inhaled drug administration requires the veterinarian to handle metered-dose inhalers and spacer devices. The veterinarian should be familiar with the equipment and ensure that the horse is properly trained to accept the mask. Systemic corticosteroids should be used with caution in horses with risk factors for laminitis.

Professional Escalation Criteria

Veterinarians should refer horses to a specialist or equine hospital in the following situations:

• Horses with severe respiratory distress that does not respond to initial treatment
• Horses with suspected complications such as pneumonia, pulmonary hemorrhage, or cardiac disease
• Horses that require advanced diagnostic testing such as pulmonary function testing, bronchoscopy, or thoracic radiography
• Horses that do not respond to standard pharmacotherapy after 8-12 weeks
• Horses with recurrent episodes of asthma despite optimal environmental control

A 2018 study on the influence of BAL on thoracic radiography found that BAL increases interstitial opacity on caudoventral and caudodorsal radiographs. The authors recommend performing thoracic radiography before BAL to avoid misinterpretation of post-procedure changes.

Practical Decision Framework for Selecting Airway Sampling Method and Interpreting Results in Equine Asthma

Clinical Decision Algorithm for BAL versus TW

The choice between bronchoalveolar lavage and tracheal wash should follow a structured decision algorithm based on the clinical question, horse signalment, and intended use of cytology results. A 2024 review of equine asthma diagnostics highlights the factors that influence test interpretation and the difficulties in diagnosing subclinical disease. The algorithm below provides a stepwise approach for veterinarians.

Step 1: Define the clinical question. Is the goal to diagnose lower airway inflammation in a horse with poor performance and cough? Is the goal to monitor response to therapy? Is the goal to rule out bacterial infection? BAL is superior for assessing lower airway inflammation, while TW may be adequate for detecting bacterial pathogens in the trachea.

Step 2: Assess the horse's signalment and use. Racehorses and high-level sport horses with mild clinical signs may have subclinical airway inflammation that is only detectable on BAL. A 2025 study comparing TW and BAL cytology in racehorses with exercise-induced pulmonary hemorrhage found that TW could not be considered a reliable alternative to BAL for comprehensive characterization of lower airway inflammation. Reliance on TW alone could lead to incomplete or misleading clinical assessments. For these horses, BAL is the preferred sampling method.

Step 3: Evaluate the clinical severity. Horses with severe respiratory distress at rest, nostril flare, and heave line likely have severe equine asthma. BAL is indicated to confirm the diagnosis and guide treatment. However, the procedure carries risks in horses with compromised respiratory function. The 2019 case report of fatal pulmonary hemorrhage during BAL underscores that horses with preexisting airway inflammation may have fragile bronchial vessels. In severely affected horses, the veterinarian should weigh the diagnostic benefit against the procedural risk.

Step 4: Consider practical constraints. Owner preference, cost, and availability of equipment may influence the choice of sampling method. TW is less invasive and may be more acceptable to owners. However, the veterinarian should explain that TW may not provide sufficient information to guide treatment decisions. A 2017 publication on equine asthma diagnosis discusses approaches beyond BAL cytology, including pulmonary function testing and airway reactivity assessment, which may be useful when BAL is not feasible.

Step 5: Document the decision. The medical record should include the rationale for selecting BAL or TW, the procedure details, and any complications. This documentation supports clinical decision-making and provides a basis for future comparisons.

Interpretation Framework for BAL Cytology Results

BAL cytology interpretation requires a systematic approach that accounts for the horse's signalment, clinical signs, and environmental exposure. The thresholds for abnormal cell percentages vary by laboratory and clinical context. The framework below provides guidance for interpreting BAL cytology results in the context of equine asthma diagnosis.

Total cell count. Normal BAL fluid contains 500-1500 cells per microliter. Increased total cell count indicates inflammation. Decreased cell count may indicate poor sample quality or dilution.

Macrophage percentage. Macrophages are the predominant cell type in normal BAL fluid, typically 50-70% of total cells. Decreased macrophage percentage suggests a shift toward other cell types, which may indicate inflammation.

Neutrophil percentage. Neutrophils are the key cell type for diagnosing equine asthma. In racehorses, neutrophil percentages above 5% are considered abnormal. In non-racehorses, the threshold is typically 10%. Horses with severe equine asthma often have neutrophil percentages exceeding 25%. A 2024 review of equine asthma diagnostics notes that neutrophil percentage is the most reliable cytologic parameter for diagnosing lower airway inflammation.

Lymphocyte percentage. Lymphocytes are normally present at 5-15% of total cells. Increased lymphocyte percentage may indicate chronic inflammation or immune stimulation. Decreased lymphocyte percentage may be seen in acute inflammation.

Mast cell percentage. Mast cells are normally present at less than 2% of total cells. Increased mast cell percentage may be associated with mild-to-moderate equine asthma in young horses. Mast cell percentages above 5% are considered abnormal.

Eosinophil percentage. Eosinophils are normally present at less than 1% of total cells. Increased eosinophil percentage may indicate parasitic infection, hypersensitivity, or drug reaction. Eosinophil percentages above 5% warrant investigation for parasitic causes.

Mucus assessment. Mucus is graded on a scale of 0-3 based on the amount and consistency. Increased mucus indicates airway inflammation and is commonly seen in equine asthma. Mucus can interfere with gas exchange and contribute to coughing.

Hemosiderophage assessment. Hemosiderophages indicate prior pulmonary hemorrhage. They are common in racehorses and can complicate cytologic interpretation. The presence of hemosiderophages does not rule out equine asthma, but the veterinarian should consider exercise-induced pulmonary hemorrhage as a differential diagnosis.

Decision Matrix for Treatment Initiation Based on BAL Cytology

The decision to initiate pharmacotherapy should be based on BAL cytology results combined with clinical signs. The matrix below provides guidance for treatment decisions.

Record System for Serial BAL Cytology Monitoring

Serial BAL cytology is essential for monitoring treatment response and adjusting therapy. The record system below provides a standardized format for tracking cytology results over time.

Horse identification. Record the horse's name, age, breed, sex, and use.

Sampling date. Record the date of each BAL procedure.

Clinical score. Record the clinical score at the time of sampling using a standardized scoring system.

Environmental assessment. Record the current environment, including hay type and treatment, bedding material, barn ventilation, and turnout schedule.

Current treatment. Record the drug, dose, route, frequency, and duration of any pharmacotherapy.

BAL cytology results. Record total cell count, differential percentages (macrophages, neutrophils, lymphocytes, mast cells, eosinophils), mucus grade, and hemosiderophage presence.

Interpretation. Record the interpretation of cytology results in the context of clinical signs and treatment.

Recommendation. Record the recommended changes to environmental management or pharmacotherapy based on cytology results.

Common Failure Patterns in BAL Cytology Interpretation

Failure pattern 1: Overinterpretation of mild neutrophilia. Mild increases in neutrophil percentage (5-10%) may be seen in horses with subclinical inflammation or recent environmental exposure. The veterinarian should correlate cytology results with clinical signs and repeat sampling after environmental modification before initiating pharmacotherapy.

Failure pattern 2: Underinterpretation of mast cell increases. Increased mast cell percentage may be the only cytologic abnormality in young horses with mild-to-moderate equine asthma. The veterinarian should not dismiss mast cell increases as insignificant. Treatment with inhaled corticosteroids may be indicated even if neutrophil percentage is normal.

Failure pattern 3: Confusion with exercise-induced pulmonary hemorrhage. Hemosiderophages on BAL indicate prior pulmonary hemorrhage, which is common in racehorses. The presence of hemosiderophages does not rule out equine asthma. The veterinarian should evaluate neutrophil percentage and clinical signs to distinguish between the two conditions.

Failure pattern 4: Sampling error due to patchy inflammation. BAL samples only a single lung lobe. Inflammation may be patchy, and a normal BAL does not rule out airway inflammation in other regions. The veterinarian should consider repeat sampling from a different lobe if clinical signs persist despite normal cytology.

Failure pattern 5: Timing error relative to treatment. Horses receiving corticosteroids may have suppressed inflammatory cell counts on BAL. The veterinarian should note the timing of sampling relative to treatment and interpret cytology results accordingly. Repeat sampling after treatment withdrawal may be necessary to assess baseline inflammation.

Troubleshooting Method for Inconsistent BAL Cytology Results

When BAL cytology results are inconsistent with clinical signs or previous results, the veterinarian should follow a systematic troubleshooting method.

Step 1: Verify sample quality. Check the volume of fluid recovered. Recovery of less than 50% of instilled volume may indicate poor sample quality. Check for blood contamination, which can dilute the sample and alter cell percentages.

Step 2: Review the procedure. Confirm that the catheter was properly wedged in a bronchus. If the catheter was not wedged, the sample may represent tracheal wash instead of BAL. Review sedation and technique to ensure consistent sampling.

Step 3: Assess environmental changes. Determine if the horse's environment has changed since the previous sampling. Horses that have been removed from dusty environments may show reduced airway inflammation. Horses that have been exposed to new triggers may show increased inflammation.

Step 4: Evaluate treatment compliance. Confirm that the horse has received the prescribed pharmacotherapy as directed. Inhaled corticosteroids may be underdosed or administered incorrectly. Systemic corticosteroids may have been tapered too quickly.

Step 5: Consider concurrent disease. Evaluate the horse for other conditions that may affect BAL cytology, such as exercise-induced pulmonary hemorrhage, bacterial pneumonia, or parasitic infection. Additional diagnostic testing may be indicated.

Step 6: Repeat sampling. If the inconsistency cannot be resolved, repeat BAL from a different lung lobe. Consider sampling from both lungs if bilateral disease is suspected.

Professional Escalation Criteria for BAL Cytology Interpretation

Veterinarians should seek consultation or refer the horse to a specialist in the following situations:

• BAL cytology results that are inconsistent with clinical signs and cannot be explained by sampling error or environmental changes
• Horses with persistent neutrophilia despite optimal environmental control and pharmacotherapy
• Horses with atypical cytology findings such as marked eosinophilia or lymphocytosis
• Horses that require advanced diagnostic testing such as pulmonary function testing, bronchoscopy, or thoracic radiography
• Horses with suspected complications such as pneumonia, pulmonary hemorrhage, or cardiac disease

A 2018 study on the influence of BAL on thoracic radiography found that BAL increases interstitial opacity on caudoventral and caudodorsal radiographs. The authors recommend performing thoracic radiography before BAL to avoid misinterpretation of post-procedure changes. This is particularly important when thoracic radiography is used to evaluate horses with suspected complications.

Practical Implementation Steps for BAL Cytology Monitoring

1. Establish a baseline BAL cytology before initiating treatment.
2. Repeat BAL cytology 4-8 weeks after initiating environmental modification and pharmacotherapy.
3. Compare cytology results to baseline to assess treatment response.
4. Adjust treatment based on cytology results and clinical signs.
5. Repeat BAL cytology every 3-6 months for horses on long-term therapy.
6. Document all cytology results in a standardized record system.
7. Communicate results to the owner and discuss treatment recommendations.

Welfare and Safety Context for BAL Cytology Monitoring

BAL is an invasive procedure that carries risks for the horse. The 2019 case report of fatal pulmonary hemorrhage during BAL underscores the importance of careful patient selection and technique. Horses with severe airway inflammation may have fragile bronchial vessels that can rupture with coughing or catheter manipulation. The veterinarian should assess the horse's respiratory status before the procedure and be prepared to manage complications.

The World Organisation for Animal Health (WOAH) emphasizes that animal health and welfare standards should include prevention and treatment of respiratory diseases. Serial BAL cytology monitoring is an important tool for ensuring that horses receive appropriate treatment and that treatment is adjusted based on objective evidence. Horses that do not respond to treatment should be evaluated for other conditions and may require referral to a specialist.

Records and Measurements for BAL Cytology Monitoring

The medical record should include the following information for each BAL procedure:

• Date and time of procedure
• Horse identification and signalment
• Clinical score at time of sampling
• Environmental assessment
• Current treatment
• Procedure details (catheter type, volume instilled, volume recovered, complications)
• Cytology results (total cell count, differential percentages, mucus grade, hemosiderophage presence)
• Interpretation
• Recommendations

Serial cytology results should be recorded in a table or spreadsheet to allow easy comparison over time. The record should also include any changes to environmental management or pharmacotherapy that were made based on cytology results.

Frequently Asked Questions

What is the difference between mild-to-moderate and severe equine asthma?

Mild-to-moderate equine asthma (previously inflammatory airway disease) typically affects young to middle-aged performance horses and causes cough, poor performance, and prolonged recovery after exercise. Severe equine asthma (previously recurrent airway obstruction or heaves) affects older horses and causes labored breathing at rest, nostril flare, heave line, and chronic cough. The distinction is based on clinical severity and BAL cytology findings.

How is equine asthma diagnosed?

Diagnosis is based on clinical signs, airway sampling with BAL or TW, and cytologic interpretation. BAL is the gold standard for assessing lower airway inflammation. TW may be used but does not reliably reflect BAL cytology. Thoracic radiography and pulmonary function testing may be used in selected cases.

What is the role of environmental control in treating equine asthma?

Environmental control is the most important intervention for managing equine asthma. Reducing exposure to dust, mold spores, and endotoxins from hay, bedding, and barn air can significantly reduce airway inflammation. Soaking or steaming hay, using low-dust bedding, and improving barn ventilation are key strategies.

What medications are used to treat equine asthma?

Corticosteroids (inhaled or systemic) are the primary anti-inflammatory drugs. Bronchodilators (beta-2 agonists or anticholinergics) are used to relieve bronchospasm. Inhaled corticosteroids are preferred for long-term management. Systemic corticosteroids are used for initial control of severe asthma.

How is treatment response monitored?

Treatment response is monitored clinically with assessment of cough frequency, respiratory rate and effort, nasal discharge, and exercise tolerance. Repeat BAL cytology after 4-8 weeks of treatment provides objective evidence of reduced airway inflammation. Lung function testing may be used in selected cases.

Can equine asthma be cured?

Equine asthma is a chronic condition that cannot be cured but can be managed effectively with environmental control and pharmacotherapy. Many horses achieve remission with appropriate management and can return to normal activity. Relapses may occur if environmental triggers are reintroduced or if treatment is discontinued.

What are the risks of bronchoalveolar lavage?

BAL is generally safe but carries risks of coughing, hemorrhage, and transient respiratory distress. A rare but serious complication is fatal pulmonary hemorrhage, which has been reported in a horse with preexisting airway inflammation. Proper sedation and technique reduce the risk of complications.

When should a horse with equine asthma be referred to a specialist?

Referral is indicated for horses with severe respiratory distress that does not respond to initial treatment, horses with suspected complications, horses that require advanced diagnostic testing, and horses that do not respond to standard pharmacotherapy after 8-12 weeks. Specialist evaluation may include pulmonary function testing, bronchoscopy, or thoracic radiography.

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References and Further Reading

• aaep.org
• www.merckvetmanual.com
• www.acvim.org
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Decision Making in Severe Equine Asthma-Diagnosis and Monitoring.. Animals : an open access journal from MDPI, 2023.
• Science-in-brief: Equine asthma diagnosis: Beyond bronchoalveolar lavage cytology.. Equine veterinary journal, 2017.
• Equine asthma: Integrative biologic relevance of a recently proposed nomenclature.. Journal of veterinary internal medicine, 2018.
• Equine Asthma Does Not Affect Circulating Myostatin Concentrations in Horses.. Animals : an open access journal from MDPI, 2024.
• Antigen array for serological diagnosis and novel allergen identification in severe equine asthma.. Scientific reports, 2019.
• Equine Asthma Diagnostics: Review of Influencing Factors and Difficulties in Diagnosing Subclinical Disease.. Animals : an open access journal from MDPI, 2024.
• Comparison Between Tracheal Wash and Bronchoalveolar Lavage Cytology for the Assessment of Airway Inflammation in Racehorses Affected by Exercise-Induced Pulmonary Hemorrhage. Animals, 2025.
• Fatal pulmonary hemorrhage in a horse during bronchoalveolar lavage - single case report. BMC Veterinary Research, 2019.
• Influence of bronchoalveolar lavage on thoracic radiography in the horse. Journal of Veterinary Sciences, 2018.
• Management of floor heave at Bulga Underground Operations - A case study. International Journal of Mining Science and Technology, 2019.
• Management of floor heave at Bulga underground operations-a case study. Proceedings of the 37th International Conference on Ground Control in Mining Icgcm 2018, 2018.
• Research on active heave compensation control of remotely operated vehicle. Zhongguo Jixie Gongcheng China Mechanical Engineering, 2009.
• Calculation method for frost heave force of tunnel with broken surrounding rock in seasonal frozen area and its engineering application. Dongnan Daxue Xuebao Ziran Kexue Ban Journal of Southeast University Natural Science Edition, 2021.
• The frost heave program of the Alaskan natural gas transportation system.. undefined, 1982.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.