FREE SHIPPING over $40
OVER 10000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
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.
Get Full Text
Publication Date: 2025-09-09 PubMed ID: 40923556DOI: 10.1111/evj.70089Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • Journal Article

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

References

This article includes 35 references
  1. Hotchkiss JW, Reid SWJ, Christley RM. A survey of horse owners in Great Britain regarding horses in their care. Part 2: risk factors for recurrent airway obstruction.. Equine Vet J 2007;39(4):301–308.
    doi: 10.2746/042516407x180129google scholar: lookup
  2. McGorum BC, Ellison J, Cullen RT. Total and respirable airborne dust endotoxin concentrations in three equine management systems.. Equine Vet J 1998;30(5):430–434.
    doi: 10.1111/j.2042-3306.1998.tb04514.xgoogle scholar: lookup
  3. Pirie RS, Dixon PM, Collie DDS, McGorum BC. Pulmonary and systemic effects of inhaled endotoxin in control and heaves horses.. Equine Vet J 2001;33(3):311–318.
    doi: 10.2746/042516401776249732google scholar: lookup
  4. Moore‐Colyer MJS, Lumbis K, Longland A, Harris P. The effect of five different wetting treatments on the nutrient content and microbial concentration in hay for horses.. PLoS One 2014;9(11):e114079.
    doi: 10.1371/journal.pone.0114079google scholar: lookup
  5. Ivester KM, Couëtil LL, Zimmerman NJ. Investigating the link between particulate exposure and airway inflammation in the horse.. J Vet Intern Med 2014;28(6):1653–1665.
    doi: 10.1111/jvim.12458google scholar: lookup
  6. Woods PSA, Robinson NE, Swanson MC, Reed CE, Broadstone RV, Derksen FJ. Airborne dust and aeroallergen concentration in a horse stable under two different management systems.. Equine Vet J 1993;25(3):208–213.
    doi: 10.1111/j.2042-3306.1993.tb02945.xgoogle scholar: lookup
  7. Leclere M, Lavoie‐Lamoureux A, Gelinas‐Lymburner E, David F, Martin JG, Lavoie JP. Effect of antigenic exposure on airway smooth muscle remodeling in an equine model of chronic asthma.. Am J Respir Cell Mol Biol 2011;45(1):181–187.
    doi: 10.1165/rcmb.2010-0300ocgoogle scholar: lookup
  8. Elia JB, Erb HN, Houpt KA. Motivation for hay: effects of a pelleted diet on behavior and physiology of horses.. Physiol Behav 2010;101(5):623–627.
    doi: 10.1016/j.physbeh.2010.09.010google scholar: lookup
  9. Westerfeld R, Payette F, Dubuc V, Manguin E, Picotte K, Beauchamp G. Effects of soaked hay on lung function and airway inflammation in horses with severe asthma.. J Vet Intern Med 2024;38(1):469–476.
    doi: 10.1111/jvim.16919google scholar: lookup
  10. Jochmans‐Lemoine A, Picotte K, Beauchamp G, Vargas A, Lavoie JP. Effects of a propriety oiled mixed hay feeding system on lung function, neutrophilic airway inflammation and oxidative stress in severe asthmatic horses.. Equine Vet J 2020;52(4):564–571.
    doi: 10.1111/evj.13218google scholar: lookup
  11. Moore‐Colyer MJS, Payne V. Palatability and ingestion behaviour of 6 polo ponies offered a choice of dry, soaked and steamed hay for 1 hour on three separate occasions.. Nottingham: Pro BSAS; 2012.
  12. Moore‐Colyer MJS, Taylor JLE, James R. The effect of steaming and soaking on the respirable particle, bacteria, mould, and nutrient content in hay for horses.. J Equine Vet Sci 2016;39:62–68.
    doi: 10.1016/j.jevs.2015.09.006google scholar: lookup
  13. Symoens A, Westerfeld R, Vives BM, André V, Moulon L, Collomb M. Steamed hay and alfalfa pellets for the management of severe equine asthma.. Equine Vet J 2025;57(3):756–765.
    doi: 10.1111/evj.14209google scholar: lookup
  14. Rush BR, Raub ES, Rhoads WS, Flaminio MJBF, Matson CJ, Hakala JE. Pulmonary function in horses with recurrent airway obstruction after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively.. Am J Vet Res 1998;59(8):1039–1043.
    doi: 10.2460/ajvr.1998.59.08.1039google scholar: lookup
  15. Tesarowski DB, Viel L, McDonell WN. Pulmonary function measurements during repeated environmental challenge of horses with recurrent airway obstruction (heaves).. Am J Vet Res 1996;57(8):1214–1219.
    doi: 10.2460/ajvr.1996.57.08.1214google scholar: lookup
  16. van Erck E, Votion D, Art T, Lekeux P. Measurement of respiratory function by impulse oscillometry in horses. Equine Vet J 2004;36(1):21–28.
    doi: 10.2746/0425164044864714google scholar: lookup
  17. Stucchi L, Ferrucci F, Bullone M, Dellaca RL, Lavoie JP. Within‐breath oscillatory mechanics in horses affected by severe equine asthma in exacerbation and in remission of the disease. Animals (Basel) 2021;12(1):4.
    doi: 10.3390/ani12010004google scholar: lookup
  18. Kaczka DW, Dellaca RL. Oscillation mechanics of the respiratory system: applications to lung disease. Crit Rev Biomed Eng 2011;39(4):337–359.
    doi: 10.1615/critrevbiomedeng.v39.i4.60google scholar: lookup
  19. Gerber V, Lindberg Å, Berney C, Robinson NE. Airway mucus in recurrent airway obstruction—short‐term response to environmental challenge. J Vet Intern Med 2004;18(1):92–97.
    doi: 10.1111/j.1939-1676.2004.tb00140.xgoogle scholar: lookup
  20. Lapointe JM, Lavoie JP, Vrins AA. Effects of triamcinolone acetonide on pulmonary function and bronchoalveolar lavage cytologic features in horses with chronic obstructive pulmonary disease. Am J Vet Res 1993;54(8):1310–1316.
    doi: 10.2460/ajvr.1993.54.08.1310google scholar: lookup
  21. Moore‐Colyer MJS, Fillery BG. The effect of three different treatments on the respirable particle content, total viable count and mould concentrations in hay for horses. 2012 p. 101–106.
  22. Raïsky C, Symoens A, Leduc L, Leclère M. Temperature variations and dust reduction with a commercial hay steamer. Presented at the Veterinary Comparative Respiratory Society 41st Symposium, Providence RI; Oct 2023.
  23. Olave CJ, Ivester KM, Couetil LL, Burgess J, Park JH, Mukhopadhyay A. Effects of low‐dust forages on dust exposure, airway cytology, and plasma omega‐3 concentrations in Thoroughbred racehorses: a randomized clinical trial. J Vet Intern Med 2023;37(1):338–348.
    doi: 10.1111/jvim.16598google scholar: lookup
  24. Orard M, Hue E, Couroucé A, Bizon‐Mercier C, Toquet M‐P, Moore‐Colyer M. The influence of hay steaming on clinical signs and airway immune response in severe asthmatic horses. BMC Vet Res 2018;14:345.
    doi: 10.1186/s12917-018-1636-4google scholar: lookup
  25. Blumerich CA. Comparison of airway response in recurrent airway obstruction‐affected horses fed steamed versus non‐steamed hay. Blacksburg: Virginia Tech; 2012.
  26. Dauvillier J, Ter Woort F, van Erck‐Westergren E. Fungi in respiratory samples of horses with inflammatory airway disease. J Vet Intern Med 2019;33(2):968–975.
    doi: 10.1111/jvim.15397google scholar: lookup
  27. Ward MP, Couëtil LL. Climatic and aeroallergen risk factors for chronic obstructive pulmonary disease in horses. Am J Vet Res 2005;66(5):818–824.
    doi: 10.2460/ajvr.2005.66.818google scholar: lookup
  28. Bullone M, Murcia RY, Lavoie JP. Environmental heat and airborne pollen concentration are associated with increased asthma severity in horses. Equine Vet J 2016;48(4):479–484.
    doi: 10.1111/evj.12559google scholar: lookup
  29. Calomeno SS, Freitas Santi TD, Barbosa B, Weber SH, Oliveira TM, Machado GF. Influence of climatic changes on respiratory health in a teaching herd of outdoor‐housed horses. Vet J 2024;307:106198.
    doi: 10.1016/j.tvjl.2024.106198google scholar: lookup
  30. Lavoie JP, Bullone M, Rodrigues N, Germim P, Albrecht B, Von Salis‐Soglio M. Effect of different doses of inhaled ciclesonide on lung function, clinical signs related to airflow limitation and serum cortisol levels in horses with experimentally induced mild to severe airway obstruction. Equine Vet J 2019;51(6):779–786.
    doi: 10.1111/evj.13093google scholar: lookup
  31. Pirie RS, Mueller HW, Engel O, Albrecht B, Von Salis‐Soglio M. Inhaled ciclesonide is efficacious and well tolerated in the treatment of severe equine asthma in a large prospective European clinical trial. Equine Vet J 2021;53(6):1094–1104.
    doi: 10.1111/evj.13419google scholar: lookup
  32. Hall JI, Lozano M, Estrada‐Petrocelli L, Birring S, Turner R. The present and future of cough counting tools. J Thorac Dis 2020;12(9):5207–5223.
    doi: 10.21037/jtd-2020-icc-003google scholar: lookup
  33. Richard EA, Fortier GD, Denoix JM, Art T, Lekeux PM, van Erck E. Influence of subclinical inflammatory airway disease on equine respiratory function evaluated by impulse oscillometry. Equine Vet J 2009;41(4):384–389.
    doi: 10.2746/042516409x366121google scholar: lookup
  34. Lo Feudo CM, Ferrucci F, Bizzotto D, Dellacà R, Lavoie JP, Stucchi L. Differences in pulmonary function measured by oscillometry between horses with mild–moderate equine asthma and healthy controls. Equine Vet J 2025;57(3):619–628.
    doi: 10.1111/evj.14206google scholar: lookup
  35. Bullone M, Chevigny M, Allano M, Martin JG, Lavoie JP. Technical and physiological determinants of airway smooth muscle mass in endobronchial biopsy samples of asthmatic horses. J Appl Physiol 2014;117(7):806–815.
    doi: 10.1152/japplphysiol.00468.2014google scholar: lookup

Citations

This article has been cited 0 times.
Subscribe to our newsletter
Join 99,928 horse owners like you who receive our email updates on horse health and nutrition.