Allano M, Labrecque O, Rodriguez Batista E Influence of short distance transportation on tracheal bacterial content and lower airway cytology in horses. Vet J. 2016; 214:47-9 10.1016/j.tvjl.2016.02.009

Argo CM, Dugdale AHA, McGowan CM Considerations for the use of restricted, soaked grass hay diets to promote weight loss in the management of equine metabolic syndrome and obesity. Vet J. 2015; 206:(2)170-7 10.1016/j.tvjl.2015.07.027

Auger EJ, Moore-Colyer MJS The effect of management regime on airborne respirable dust concentrations in two different types of horse stable design. J Equine Vet Sci. 2017; 51:105-9 10.1016/j.jevs.2016.12.007

Berndt A, Derksen FJ, Edward Robinson N Endotoxin concentrations within the breathing zone of horses are higher in stables than on pasture. Vet J. 2010; 183:(1)54-7 10.1016/j.tvjl.2008.09.001

Blackman M, Moore-Colyer MJS Hay for horses: the effects of three different wetting treatments on dust and nutrient content. Animal Science. 1998; 66:(03)745-50 10.1017/S1357729800009334

Bullone M, Murcia RY, Lavoie J-P Environmental heat and airborne pollen concentration are associated with increased asthma severity in horses. Equine Vet J. 2016; 48:(4)479-84 10.1111/evj.12559

Carslake HB, Argo CM, Pinchbeck GL, Dugdale AHA, McGowan CM Insulinaemic and glycaemic responses to three forages in ponies. Vet J. 2018; 235:83-9 10.1016/j.tvjl.2018.03.008

Clarke AF A review of environmental and host factors in relation to equine respiratory disease. Equine Vet J. 1987; 19:(5)435-41

Clements JM, Pirie RS Respirable dust concentrations in equine stables. Part 1: validation of equipment and effect of various management systems. Res Vet Sci. 2007a; 83:(2)256-62 10.1016/j.rvsc.2006.12.002

Clements JM, Pirie RS Respirable dust concentrations in equine stables. Part 2: the benefits of soaking hay and optimising the environment in a neighbouring stable. Res Vet Sci. 2007b; 83:(2)263-8 10.1016/j.rvsc.2006.12.003

Costa LRR, Johnson JR, Baur ME, Beadle RE Temporal clinical exacerbation of summer pasture-associated recurrent airway obstruction and relationship with climate and aeroallergens in horses. Am J Vet Res. 2006; 67:(9)1635-42 10.2460/ajvr.67.9.1635

Couëtil LL, Cardwell JM, Gerber V, Lavoie JP, Léguillette R, Richard EA Inflammatory airway disease of horses-revised consensus statement. J Vet Intern Med. 2016; 30:(2)503-15 10.1111/jvim.13824

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)968-75

Derksen FJ, Olszewski MA, Robinson NE, Berney C, Hakala JE, Matson CJ, Ruth DT Aerosolized albuterol sulfate used as a bronchodilator in horses with recurrent airway obstruction. Am J Vet Res. 1999; 60:(6)689-3

Dixon PM, Railton DI, McGorum BC Equine pulmonary disease: a case control study of 300 referred cases. Part 2: Details of animals and of historical and clinical findings. Equine Vet J. 1995a; 27:(6)422-7 10.1111/j.2042-3306.1995.tb04422.x

Dixon PM, Railton DI, McGorum BC, Tothill S Equine pulmonary disease: a case control study of 300 referred cases. Part 4: Treatments and re-examination findings. Equine Vet J. 1995b; 27:(6)436-9 10.1111/j.2042-3306.1995.tb04424.x

Earing JE, Hathaway MR, Sheaffer CC Effect of hay steaming on forage nutritive values and dry matter intake by horses1. J Anim Sci. 2013; 91:(12)5813-20 10.2527/jas.2013-6333

Fleming K, Hessel EF, Van den Weghe HFA Generation of airborne particles from different bedding materials used for horse keeping. J Equine Vet Sci. 2008; 28:(7)408-18 10.1016/j.jevs.2008.05.004

Harris PA, Ellis AD, Fradinho MJ Review: Feeding conserved forage to horses: recent advances and recommendations. Animal. 2017; 11:(06)958-67 10.1017/S1751731116002469

Herszberg B, Ramos-Barbón D, Tamaoka M, Martin JG, Lavoie JP Heaves, an asthma-like equine disease, involves airway smooth muscle remodeling. J Allergy Clin Immunol. 2006; 118:(2)382-8 10.1016/j.jaci.2006.03.044

Hessel EF, Garlipp F, Van den Weghe HFA Generation of airborne particles from horse feeds depending on type and processing. J Equine Vet Sci. 2009; 29:(9)665-74 10.1016/j.jevs.2009.07.013

Holcombe SJ, Jackson C, Gerber V, Jefcoat A, Berney C, Eberhardt S, Robinson NE Stabling is associated with airway inflammation in young Arabian horses. Equine Vet J. 2001; 33:(3)244-9 10.2746/042516401776249606

Hotchkiss JW, Reid SWJ, Christley RM A survey of horse owners in Great Britain regarding horses in their care. Part 1: horse demographic characteristics and management. Equine Vet J. 2007a; 39:(4)294-300 10.2746/042516407X177538

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. 2007b; 39:(4)301-8 10.2746/042516407X180129

Houtsma A, Bedenice D, Pusterla N Association between inflammatory airway disease of horses and exposure to respiratory viruses: a case control study. Multidiscip Respir Med. 2015; 10:(1) 10.1186/s40248-015-0030-3

Ivester KM, Couëtil LL Management of chronic airway inflammation in the horse: A systematic review. Equine Vet Educ. 2014; 26:(12)647-56 10.1111/eve.12238

Ivester KM, Smith K, Moore GE, Zimmerman NJ, Couëtil LL Variability in particulate concentrations in a horse training barn over time. Equine Vet J. 2012; 44:(43)51-6 10.1111/j.2042-3306.2012.00647.x

Ivester KM, Couëtil LL, Moore GE, Zimmerman NJ, Raskin RE Environmental exposures and airway inflammation in young thoroughbred horses. J Vet Intern Med. 2014; 28:(3)918-24 10.1111/jvim.12333

Ivester KM, Couëtil LL, Moore GE An observational study of environmental exposures, airway cytology, and performance in racing thoroughbreds. J Vet Intern Med. 2018; 32:(5)1754-62 10.1111/jvim.15226

Jackson CA, Berney C, Jefcoat AM, Robinson NE Environment and prednisone interactions in the treatment of recurrent airway obstruction (heaves). Equine Vet J. 2000; 32:(5)432-8 10.2746/042516400777591165

Kirschvink N, Di Silvestro F, Sbaï I The use of cardboard bedding material as part of an environmental control regime for heaves-affected horses: in vitro assessment of airborne dust and aeroallergen concentration and in vivo effects on lung function. Vet J. 2002; 163:(3)319-25 10.1053/tvjl.2001.0658

Leclere M, Lavoie-Lamoureux A, Joubert P Corticosteroids and antigen avoidance decrease airway smooth muscle mass in an equine asthma model. Am J Respir Cell Mol Biol. 2012; 47:(5)589-96 10.1165/rcmb.2011-0363OC

Mack SJ, Dugdale AH, Argo CM, Morgan RA, McGowan CM Impact of water-soaking on the nutrient composition of UK hays. Vet Rec. 2014; 174:(18) 10.1136/vr.102074

Mair TS Obstructive pulmonary disease in 18 horses at summer pasture. Vet Rec. 1996; 27:(4)89-91 10.1136/vr.138.4.89

McGorum BC, Dixon PM, Halliwell REW Responses of horses affected with chronic obstructive pulmonary disease to inhalation challenges with mould antigens. Equine Vet J. 1993; 25:(4)261-7 10.1111/j.2042-3306.1993.tb02960.x

McGorum BC, Ellison J, Cullen RT Total and respirable airborne dust endotoxin concentrations in three equine management systems. Equine Vet J. 1998; 30:(5)430-4 10.1111/j.2042-3306.1998.tb04514.x

Millerick-May ML, Karmaus W, Derksen FJ, Berthold B, Holcombe SJ, Robinson NE Particle mapping in stables at an American Thoroughbred racetrack. Equine Vet J. 2011; 43:(5)599-607 10.1111/j.2042-3306.2010.00331.x

Miskovic M, Couëtil LL, Thompson CA Lung function and airway cytologic profiles in horses with recurrent airway obstruction maintained in low-dust environments. J Vet Intern Med. 2007; 21:(5)1060-6 10.1111/j.1939-1676.2007.tb03065.x

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) 10.1371/journal.pone.0114079

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; 39:62-8 10.1016/j.jevs.2015.09.006

Oliver BGG, Robinson P, Peters M, Black J Viral infections and asthma: an inflammatory interface?. Eur Respir J. 2014; 44:(6)1666-81 10.1183/09031936.00047714

Orard M, Hue E, Couroucé A The influence of hay steaming on clinical signs and airway immune response in severe asthmatic horses. BMC Vet Res. 2018; 14:(1) 10.1186/s12917-018-1636-4

Pirie RS Recurrent airway obstruction: A review. Equine Vet J. 2014; 46:(3)276-88 10.1111/evj.12204

Pirie RS, Dixon PM, McGorum BC Evaluation of nebulised hay dust suspensions (HDS) for the diagnosis and investigation of heaves. 3: effect of fractionation of HDS. Equine Vet J. 2002; 34:(4)343-7 10.2746/042516402776249236

Pirie RS, Collie DDS, Dixon PM, McGorum BC Inhaled endotoxin and organic dust particulates have synergistic proinflammatory effects in equine heaves (organic dust-induced asthma). Clin Exp Allergy. 2003; 33:(5)676-83 10.1046/j.1365-2222.2003.01640.x

Pirie RS, Couëtil LL, Robinson NE, Lavoie J-P Equine asthma: an appropriate, translational and comprehendible terminology?. Equine Vet J. 2016; 48:(4)403-5 10.1111/evj.12586

Robinson NE, Berney C, Eberhart S Coughing, mucus accumulation, airway obstruction, and airway inflammation in control horses and horses affected with recurrent airway obstruction. Am J Vet Res. 2003; 64:(5)550-7 10.2460/ajvr.2003.64.550

Séguin V, Garon D, Lemauviel-Lavenant S How to improve the hygienic quality of forages for horse feeding. J Sci Food Agric. 2012; 92:(4)975-86 10.1002/jsfa.4680

Siegers EW, Anthonisse M, van Eerdenburg FJCM, van den Broek J, Wouters IM, Westermann CM Effect of ionization, bedding, and feeding on air quality in a horse stable. J Vet Intern Med. 2018; 32:(3)1234-40 10.1111/jvim.15069

Tanner MK, Swinker AM, Beard ML Effect of phone book paper versus sawdust and straw bedding on the presence of airborne gram-negative bacteria, fungi and endotoxin in horse stalls. J Equine Vet Sci. 1998; 18:(7)457-61 10.1016/S0737-0806(98)80038-5

Thomson JR, McPherson EA Effects of environmental control on pulmonary function of horses affected with chronic obstructive pulmonary disease. Equine Vet J. 1984; 16:(1)35-8 10.1111/j.2042-3306.1984.tb01845.x

Vandenput S, Votion D, Duvivier DH Effect of a set stabled environmental control on pulmonary function and airway reactivity of COPD affected horses. Vet J. 1998; 155:(2)189-95 10.1016/S1090-0233(98)80018-X

Ward PL, Wohlt JE, Katz SE Chemical, physical, and environmental properties of pelleted newspaper compared to wheat straw and wood shavings as bedding for horses. J Anim Sci. 2001; 79:(6)1359-69 10.2527/2001.7961359x

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)208-13 10.1111/j.2042-3306.1993.tb02945.

Equine asthma: managing the environment

02 November 2022
12 mins read
Volume 6 · Issue 6
Figure 2. A converted bin used for soaking a bale (or less) of hay. Note the brass drainage hole bottom right.
Figure 2. A converted bin used for soaking a bale (or less) of hay. Note the brass drainage hole bottom right.


Equine asthma is an umbrella term defined by nonseptic lower airway inflammation. Currently there are two broad categories, namely mild to moderate equine asthma (formerly known as inflammatory airway disease) and severe equine asthma (formerly known as recurrent airway obstruction or heaves). Environmental challenge is involved in the aetiopathogenesis of both these subcategories. Much of this challenge, and the part that we can control, is provided by the organic dust associated with the stabling of horses. This article reviews the available evidence relating to the environmental management of equine asthma and tries to relate this to practical options for providing a low-dust environment.

The term equine asthma is used to describe nonseptic lower airway inflammation under a broad phenotypic definition that allows for multiple, potentially overlapping, subcategories of disease (Pirie et al, 2016). This umbrella term is designed to cover the diversity in aetiology, immunology, pathophysiology, genetics and clinical severity undoubtedly underpinning the disease syndrome; it is not a continuum. Currently we are restricted to two categories, mild to moderate equine asthma and severe equine asthma, these being predominantly differentiated by the presence at rest of increased respiratory effort in the latter (Couëtil et al, 2016). Mild to moderate equine asthma has previously been called inflammatory airway disease (IAD), while severe equine asthma has been known as chronic obstructive pulmonary disease (COPD), recurrent airway obstruction (RAO) and ‘heaves’.

Severe equine asthma's clinical signs, ranging from poor performance to coughing and expiratory dyspnoea, can be attributed to lower airway inflammation induced by immunological responses, including hypersensitivity, to airborne organic dust. A myriad of different agents present in a horse's stabled environment can contribute to the aetiology of this disease, with moulds having a principle role along with endotoxins (Pirie et al, 2003; Pirie, 2014). Horses with severe equine asthma have increased airway reactivity, thus non-specific stimuli such as other particulates and irritant gases, for example ammonia, may exacerbate or prolong clinical signs (Pirie, 2014). Severe equine asthma is generally associated with stabling, which is unavoidable in many situations or climates, especially during winter. However, not all severe equine asthma is associated with housing, as recognised in the subset of equine pasture asthma (formerly summer pasture associated obstructive pulmonary disease), where inciting agents have been suggested to be pollens and fungal spores in association with heat and humidity (Costa et al, 2006; Bullone et al, 2016). The management changes discussed in this article will not be of direct benefit to such horses, but removal to a low-dust housed environment is a standard recommendation.

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