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Home / Equine Research Bank / Equine Vet J / Steamed hay for the prevention of severe equine asthma exace...
Equine veterinary journal2025; doi: 10.1111/evj.70089

Steamed hay for the prevention of severe equine asthma exacerbations.

Abstract: Steaming hay reduces respirable particles and is commonly used to feed horses with asthma. However, it showed inconsistent benefits in clinical studies. Objective: (1) To assess the effects of steamed hay on lung function and airway inflammation in horses with severe equine asthma (SEA) in remission; (2) To compare these effects with a dry hay diet. Methods: Cross-over in vivo experiment. Methods: Horses were fed steamed and dry hay for 4 weeks in a prospective, cross-over study, with a 4-week washout period. Lung function, bronchoalveolar lavage (BALF) cytology, and a 23-point weighted clinical score (WCS) were recorded before and after 4 weeks of hay feeding. A mixed linear model with post hoc tests was used. Results: Resistance at 5 Hz (R5) increased over the 4-week period (time effect and post hoc end vs. baseline: p < 0.001), with no difference between treatments (mean [SD], kPa/L/s) (baseline dry: 0.065 [0.014]; end dry: 0.079 [0.019]; baseline steamed: 0.063 [0.009]; end steamed: 0.078 [0.014]). There was a significant increase in BALF neutrophil percentages over time (end vs. baseline: p < 0.001) (baseline dry: 6.7 [5.4]; end dry: 13.1 [6.0]; baseline steamed: 5.6 [2.6]; end steamed: 10.5 [4.3]). WCS did not change significantly (baseline dry: 2.6 [1.5]; end dry: 2.2 [1.2]; baseline steamed: 2.9 [1.5]; end steamed: 1.9 [1.3]). Conclusions: This study involves small number of horses in a research setting. Hay dust content and particles in the breathing zone were not measured. Conclusions: Steamed hay induced a mild but significant deterioration of lung function and inflammation in horses with SEA. The lack of differences with dry hay could be due to the unexpectedly mild exacerbation during this study. Unassigned: Das Bedampfen von Heu reduziert die lungengängigen Partikel und wird häufig zur Fütterung von Pferden mit Asthma eingesetzt. In klinischen Studien zeigte sich jedoch ein uneinheitlicher Nutzen. ZIELE: (1) Bewertung der Auswirkungen von bedampftem Heu auf die Lungenfunktion und die Entzündung der Atemwege bei Pferden mit schwerem Equinem Asthma (SEA) in Remission (2) Vergleich dieser Auswirkungen mit einer Fütterung bestehend aus trockenem Heu. Methods: Cross‐over in‐vivo experiment. Methods: In einer prospektiven Cross‐over‐Studie wurden Pferde 4 Wochen lang mit bedampftem und trockenem Heu gefüttert, mit einer 4‐wöchige Auswaschphase. Die Lungenfunktion, die Zytologie der bronchoalveolären Lavage (BALF) und ein gewichteter klinischer 23‐Punkte‐Score (WCS) wurden vor und nach der vierwöchigen Heufütterung erfasst. Es wurde ein gemischtes lineares Modell mit Post‐hoc‐Tests verwendet. Unassigned: Der Widerstand bei 5 Hertz (R5) nahm über den Zeitraum von 4 Wochen zu (Zeiteffekt und post‐hoc Ende gegenüber Ausgangssituation: p < 0,001), wobei kein Unterschied zwischen den Behandlungen bestand (Mittelwert (SD), kPa/L/s) (Ausgangssituation trocken: 0,065 (0,014); Ende trocken: 0,079 (0,019); Ausgangssituation bedampft: 0,063 (0,009); Ende bedampft: 0,078 (0,014)). Der Anteil der neutrophilen Granulozyten in der BALF stieg im Laufe der Zeit signifikant an (Ende im Vergleich zum Ausgangswert: p < 0,001) (Ausgangswert trocken: 6,7 (5,4); Ende trocken: 13,1 (6,0); Ausgangswert bedampft: 5,6 (2,6); Ende bedampft: 10,5 (4,3)). Die WCS veränderte sich nicht signifikant (Ausgangswert trocken: 2,6 (1,5); Endwert trocken: 2,2 (1,2); Ausgangswert bedampft: 2,9 (1,5); Endwert bedampft: 1,9 (1,3)). Unassigned: Kleine Anzahl von Pferden in einer Forschungsumgebung. Heustaubgehalt und Partikel in der Atemzone wurden nicht gemessen. Unassigned: Bedampftes Heu führte bei Pferden mit SEA zu einer leichten, aber signifikanten Verschlechterung der Lungenfunktion und Entzündung. Das Fehlen von Unterschieden zu trockenem Heu könnte auf die unerwartet leichte Exazerbation während dieser Studie zurückzuführen sein.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2025-09-09 PubMed ID: 40923556DOI: 10.1111/evj.70089Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated whether feeding steamed hay, compared to dry hay, improves lung function and airway inflammation in horses with severe equine asthma (SEA) in remission.
  • The research aimed to determine if steaming hay could prevent asthma exacerbations by reducing respirable dust particles, which are known to aggravate the condition.

Background and Rationale

  • Severe equine asthma (SEA) is a chronic inflammatory lung disease triggered by airborne particles such as dust and molds commonly found in hay.
  • Steaming hay is commonly used to reduce these respirable particles before feeding horses and is believed to help prevent asthma attacks.
  • Previous clinical studies showed inconsistent benefits from steamed hay, necessitating further controlled research.

Study Objectives

  • Primary: To assess the effects of steamed hay on lung function and airway inflammation in horses with SEA during remission (i.e., stable phase without active symptoms).
  • Secondary: To compare the effects of steamed hay with those of a dry hay diet over a 4-week period.

Study Design and Methods

  • The study used a prospective, cross-over in vivo experimental design.
  • Horses with SEA were fed steamed hay for 4 weeks and dry hay for 4 weeks, separated by a 4-week washout period to minimize carryover effects.
  • Key measurements were recorded before and after each 4-week feeding period:
    • Lung function, focusing on respiratory resistance measured at 5 Hz (R5)
    • Bronchoalveolar lavage fluid (BALF) cytology to measure airway inflammation, specifically neutrophil percentages
    • A 23-point weighted clinical score (WCS) to assess clinical signs of asthma
  • Statistical analysis was performed using a mixed linear model with post hoc tests to evaluate time and treatment effects.

Results

  • Lung Function (Resistance at 5 Hz, R5):
    • R5 increased significantly over the 4-week period regardless of hay type, indicating worsening airway resistance (p < 0.001).
    • No significant difference between steamed and dry hay groups was observed in the change of lung resistance values.
    • Mean R5 values increased from approximately 0.065 to 0.079 kPa/L/s for dry hay and from 0.063 to 0.078 kPa/L/s for steamed hay.
  • Airway Inflammation (BALF Neutrophils):
    • The percentage of neutrophils in BALF increased significantly over time in both groups (p < 0.001), indicating increased airway inflammation.
    • Neutrophil percentages rose from about 6.7% to 13.1% (dry hay) and 5.6% to 10.5% (steamed hay).
    • No significant difference between diet types was found for neutrophil increase.
  • Clinical Signs (WCS):
    • The weighted clinical score did not change significantly in either group over the feeding periods, suggesting no noticeable exacerbation of clinical signs.
    • Baseline and end scores were roughly similar, indicating mild or stable clinical status during the study.

Interpretation of Findings

  • Contrary to expectations, steamed hay did not prevent deterioration in lung function or airway inflammation compared to dry hay.
  • Both types of hay led to increased airway resistance and neutrophilic inflammation over 4 weeks, although clinical signs remained stable.
  • The lack of significant differences between steamed and dry hay might be explained by the mild severity of asthma exacerbations in this controlled research setting.
  • The study did not measure dust content or particle concentration in the breathing zone, which are important variables influencing airway responses.

Limitations

  • Small number of horses studied, limiting the statistical power and generalizability of findings.
  • Research setting may not fully replicate natural environmental exposure conditions.
  • Absence of direct measurement of dust and particulate matter exposure during feeding.
  • Possible mild asthma exacerbation during the study could have masked potential benefits of steamed hay.

Conclusions

  • Steaming hay induced a mild but statistically significant worsening of lung function and airway inflammation in horses with SEA, similar to dry hay feeding.
  • Steamed hay did not confer measurable protection against asthma exacerbations compared to dry hay in this particular study setup.
  • Further research with larger sample sizes, natural exposure settings, and direct dust measurements is needed to clarify the clinical utility of steamed hay for managing severe equine asthma.

Cite This Article

APA
Raïsky C, Vives BM, Leduc L, Symoens A, Tavanaeimanesh H, Richard H, Juette T, Bédard C, Leclère M. (2025). Steamed hay for the prevention of severe equine asthma exacerbations. Equine Vet J. https://doi.org/10.1111/evj.70089

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Raïsky, Clara
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Vives, Berta Mozo
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Leduc, Laurence
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Symoens, Antoine
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Tavanaeimanesh, Hamid
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Richard, Hélène
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Juette, Tristan
  • Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Bédard, Christian
  • Department of Pathology and Microbiology, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.
Leclère, Mathilde
  • Department of Clinical Sciences, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada.

Grant Funding

  • Equine Health Fund of the Université de Montréal (supported by Zoetis)
  • Fonds du Centenaire of the Université de Montréal
  • Haygain Limited

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