When the Moreton BE90 section H winner, Boby, suddenly started struggling to make the time across country last summer, alarm bells rang for his owner-rider, Sheila Williams.

“He never showed any external signs of breathing difficulties – no coughing or wheezing – but he wasn’t comfortable going at a fast pace, so I had him scoped to find out what was going on,” revealed Sheila of the 11-year-old part-Welsh cob gelding known as Harley, who was bought as a lockdown project two years ago but has since become a permanent fixture in her Bridgwater yard.

Harley was diagnosed with equine asthma, a condition that has to be carefully managed through the daily use of a nebuliser mask which dispenses liquid steroids.

“He has to wear the mask for 20 minutes every day, and then in the medicine withdrawal period in the lead-up to an event I substitute the steroids for a product called Audevard Balsamic Air [which is competition legal] and was recommended to me by Lissa Green, who uses it on one of her horses,” explained Sheila. “He’s incredibly tolerant of it all, which is testament to his amazing temperament.”

The pair headed BE90 section H, conquering the optimum time to finish on their dressage score of 28.

Sheila Williams, who works part-time as a cleaner to fund her hobby, has her sights set on qualifying for next year’s Badminton grassroots championship.

“I competed there five years ago with another horse and it would be a dream to go back again with Harley,” she added.

Read more from Moreton in this week’s Horse & Hound magazine, dated 31 March. 

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• This article has been edited and approved by Karen Coumbe MRCVS, H&H’s veterinary advisor since 1991.

Horses with equine asthma suffer from inflammation and/or obstruction of the lower airway so are unable to breathe as well as a healthy horse. An accumulation of excessive mucus in their airways can cause the horse to cough from time to time and affects their ability to exercise, while severe cases show a clear increased effort to breath while at rest, traditionally referred to as heaves or being broken-winded.

This condition, which has previously been described as chronic obstructive pulmonary disease (COPD), is now widely referred to within the veterinary community as ‘equine asthma’. Research has shown¹ it is more closely aligned to asthma in humans than it is to COPD, which is typically caused by chronic smoking or exposure of the human lungs to other damaging substances.

Equine asthma can be mild to moderate, when it is termed inflammatory airway disease (IAD), or severe, when it is described as recurrent airway obstruction (RAO). IAD is typically seen in young to middle aged horses, although it can be found in horses of any age. RAO is most often seen in horses over seven years of age.

Equine asthma: Signs | Causes | Diagnosis | Treatment | Prognosis 

Signs of equine asthma

In mild to moderate cases (IAD) a horse will cough occasionally both at rest and during exercise for four weeks or more and a loss of performance will be seen.

This loss in performance may be subtle, and may go unnoticed, especially in mild cases where the horse is not in hard work. Some cases will improve following changes to management while others will require treatment, but the risk of recurrence is low as long as the necessary management changes are maintained.

In severe cases of equine asthma (otherwise refered to as RAO) the coughing will be more frequent, the ability to perform will be more significantly impacted and a clear effort to breathe at rest will be seen. The severity may vary over time and may last for weeks to months before being diagnosed. Signs of RAO usually improve with strict environmental control and/or treatment, but the condition cannot be cured.

Not all cases of IAD will become ROA, although an untreated case of IAD could develop into ROA over time. These conditions have the potential to be debilitating and performance-limiting and are reported to affect 14% of horses in the northern hemisphere.

New research is being done to look at the different allergens that are involved in severe equine asthma² and also biomarkers³, which are measurable substances in the body, particularly the blood. The hope is that over time these can be used to correctly identify affected horses.

What causes equine asthma?

Stable dust, as well as fungi, mold spores, bacterial products and other irritant particles found in forage and bedding, is a primary cause of equine asthma. When horses at pasture are affected, the stimuli are most commonly pollen and dust particles. Some horses show more obvious signs when the weather is hot/humid or when pollen levels are high.

How is it diagnosed?

Your vet will diagnose equine asthma based on the horse’s history, management and clinical signs.

The obvious clinical clues are a cough at rest or at exercise (especially on gait changes), a white nasal discharge, a raised breathing rate and poor performance, particularly rapid fatigue and a prolonged high breathing rate after exercise.

Airway endoscopy– most commonly standing at rest or while exercising either on a treadmill or more likely via exercise endoscopy – can be used to ascertain the severity of the condition.

Fluid sampling of the discharges within the airways enables the severity of the airway inflammation to be assessed. This can be done by:

• Either a tracheal wash, where fluid is sampled from the trachea
• Or bronchoalveolar lavage, when a sample is collected from the lower airways.

Healthy horses have either no or very little mucus in their airway. Poor performance can occur with a tracheal mucus score of 2/5 in racehorses and 3/5 in sports horses. The fluid can then by analysed under the microscope and the different cells checked, particularly neutrophils, eosinophils and mast cells.

In mild to moderate equine asthma, bronchoalveolar lavage is recommended, If there is a neutrophil percentage of more than 6% in racehorses or 10% in sport horses , it can be sufficient to affect performance.

Management and treatment

Dealing with equine asthma effectively is likely to require both day-to-day management changes and medical treatment.

It is important to try to prevent exposure to causal factors, such as dusty hay and bedding. Choosing a dust-free bedding option and soaking hay for at least 30 minutes or feeding haylage will be beneficial. Steaming hay with a Haygain steamer or other effective steaming system is useful, but rinsing hay is not sufficient and homemade steamers are unlikely to work effectively. Horses that are stabled part or all of the time should be kept in well-ventilated areas with dust-free bedding, such as good quality shavings or paper. A well-ventilated stable should have at least one square metre of open space, achieved by using door chain or bars, opening or removing windows. This ventilation space should start below the horse’s muzzle level.

If a horse is badly affected when the weather is hot/humid or when pollen levels are high, exposure to these conditions should be avoided as far as possible. It is hard to make recommendations other than to keep the horse in the windiest field or bring them in. Environmental management is essential in all cases. The two key aspects are to reduce exposure to allergens in the air and improve ventilation.

Medication is also used. Oral bronchodilators (inhaled medication to open up the airways) in conjunction with steroids are the basis for initial treatment. Inhaled medication, very much like in human medicine, can be administered via an inhaler or nebuliser. If the horse is due to compete or race, check with your vet whether the medication is allowed under FEI or BHA rules.

There is a wide range of nutritional respiratory supplements on sale that have been formulated purporting to help support healthy airways in order to maximize equine health and performance. However, under Veterinary Medicines Directorate rules, nutritional supplements cannot claim to treat an established medical condition.

Prognosis

Once diagnosed, most horses with equine asthma will regain their ability to exercise at their former level once they have undergone treatment and their management has been adjusted to suit their needs. However, the condition will not disappear and will need to continue to be monitored and management changes made as required.

References:

• Inflammatory Airway Disease of Horses—Revised Consensus Statement – March/April 2016
• Antigen array for serological diagnosis and novel allergen identification in severe equine asthma – October 2019
• Investigation of blood biomarkers for the diagnosis of mild to moderate asthma in horses – July 2019

The colder months can challenge a horse’s airway function, at work and rest. Richard Hepburn FRCVS offers solutions for the season ahead

Winter is the perfect time to reassess your horse’s stable management, with the aim of improving the quality of his breathing zone.

We saw in part one of this series how creating a cleaner indoor living environment, with fewer airborne particles, will reduce the likelihood of airway inflammation and the subsequent development of equine asthma (EA).

Yet both turnout and exercise can create additional breathing challenges…

Arena exercise

The concentration of respirable particles in an indoor arena is dependent upon its setting and construction, both the type and humidity of its surface and the number of horses being trained at the same time.

Working a horse on a surface liberates particles, which are then dispersed into the school environment. An increased number of horses using the school will worsen this, with trotting and galloping producing the greatest quantity of respirable particles.

While the effect of different surface types is unclear, the release of particles from damp surfaces is less than that from the same surface when dry. This may be related to surface penetration: when the material is dry, a horse’s feet will sink more deeply and disperse a greater amount of material.

Further factors will affect arena air quality. If connecting doors to stables are left open during mucking out or forage feeding, this will increase respirable particle levels. Improvements will occur, however, after cleaning the arena border and solid surfaces including seating and obstacles, to remove dust and contamination.

Ventilation from the outside, away from other sources of dust such as stables, access roads, parking areas and muck heaps, will also help.

Key message: close connecting doors to stables, but open any windows that will let clean air in, and keep the school surface well-dampened and its surroundings dust-free. A horse with EA should be exercised alone indoors, ideally before others or after a period of ventilation.

Outdoor work

Strenuous exercise in cold air has been shown to produce prolonged suppression of local immunity within the lungs, which researchers postulate could increase the risk of respiratory viral infection such as equine influenza. It is unknown if this reduction in immune function has any effect on allergic airway disease, so the traditional advice that a good blast in the cold will help the lungs is unproven.

Exercising in temperatures below freezing can cause bronchoconstriction, where the airway narrows due to contraction of the surrounding muscle. This can occur any time, from immediately afterwards to several hours later, in otherwise healthy horses. We don’t yet know whether underlying environmental airway inflammation makes this more likely.

Key message: if your horse has a high breathing rate or is coughing after exercise on a cold day, consult your vet.

Turnout

The ultimate improvement in air quality is pasture turnout, which can significantly reverse airway inflammation in severe EA cases. It is important, however, to consider areas where ventilation may not be improved – most importantly, in field shelters and with feeding arrangements.

Follow the same advice as if the horse was in a stable, ensuring that shelters are airy, clean and free of dusty bedding. If you want to feed dry hay, place it outside on the ground. Similarly, consider whether hard feed in a bucket is a source of respirable particles; if necessary, wet the feed.

If you need to use round bales, split them open and position them in the windiest spot of the field.

Key message: consider your horse’s breathing zone, particularly where he can create a small, poorly ventilated area by tunnelling into dry forage. Soaked or steamed hay is a better option for the EA sufferer.

Grand designs

Ventilation of buildings is a key factor in airway health. It’s worth considering the movement of air around a horse’s living quarters – not just for the EA sufferer, but with any horse spending more than a few hours indoors.

Increasing natural ventilation is an effective way of reducing respirable particles, yet the benefit within an individual stable or barn is variable and very localised. Particles must be cleared from the air before the horse inhales them, so any ventilation must be targeted at the horse’s breathing zone – the area at nostril height.

When building new stables, the air quality in this all-important breathing zone can be considered within the design. For most, however, it’s a case of working with existing buildings and modifying them where possible.

Mechanical ventilation is aimed at replacing inadequate natural ventilation, so any design or benefit will be specific to a particular stable or barn. Agricultural engineers with experience in calf and dairy cow housing are usually the best people to approach for advice.

To maximise airflow and enhance air quality in a stable setting, consider:

• Bars or grills on the top of stable doors and partitions, or slots between the boards.
• No ceiling, with an interior that opens to the roof peak.
• Steamed or soaked forage, ideally fed from the floor.
• Siting the stable in a windy location, away from outside sources of respirable particles, so that openable windows admit clean air.
• “Breathable walls” on the outer barn building, created by leaving gaps within the wall material or using mesh between structural supports.
• Low-dust bedding – for all stables in a barn setting.
• A sealed, padded floor, to reduce the amount of bedding needed.
• An adjoining outdoor area, so the horse can choose to be in or out

Asthma alert

Exposure to barn stabling is a risk factor for human asthma. Indeed, the equine and human diseases are thought to be so similar that an understanding of the causative environmental factors can benefit both horses and their owners.

If your horse’s EA signs persist, despite efforts to improve his air quality, talk to your vet about an appropriate treatment plan. New options include supplementation with docosahexaenoic acid (DHA), which can reduce the time taken for environmental modification to improve airway health, and an equine-specific corticosteroid asthma inhaler – an effective treatment with no systemic side effects. Ask your vet for details

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Latex in some riding surfaces could contribute to the risk of severe equine asthma (sEA) — but more research is needed.

The study, conducted by researchers from the Royal Agricultural University and the University of Nottingham, funded by Haygain and the Fred and Marjory Sainsbury Trust, aimed to identify allergens associated with sEA. The scientists assessed the presence of specific antibodies to almost 400 allergenic proteins in the blood of 138 healthy horses and horses with sEA.

A mathematical model was used to rank the allergens to determine whether horses were affected.

Results confirmed previously identified allergens such as those found in mould, and dust, but also identified those found in natural rubber latex.

It found four of the top six allergens had latex molecules. These can be inhaled in dust from some riding surfaces.

Lead researcher Samuel White told H&H it was the widest allergen assessment in sEA horses to date, and latex was “surprising”.

“Before we say it is a definite risk we need further research to look at exposure levels, and at the effect latex molecules have on the immune system,” he said.

Mr White said by identifying allergens, owners can implement “effective avoidance regimes”.

“If we’re able to identify allergens we can avoid them — the cornerstone to effective treatment — and it enables advancements in diagnostics and treatment.

“By liaising with manufacturers we could identify potential risk factors or concerns so we can remedy them where possible and produce a surface that optimises health, welfare and performance,” he said.

David Rendle, equine internal medicine specialist and member of the British Equine Veterinary Association health and medicines committee, told H&H the study is “very interesting” but added it would be rash to draw conclusions on using artificial surfaces.

“The presence of antibodies does not confirm a significant role in disease, and further studies are warranted to corroborate these findings and confirm a link with lung pathology,“ he said.

“It is likely airborne pollutants in the stable will remain the major factor in sEA, and owners of horses with or without signs of airway disease should continue to focus on improving air hygiene in stables while taking reasonable precautions to reduce dust in schools and other outdoor areas.”

A spokesman for Andrews Bowen Ltd told H&H the surface manufacturer does not use rubber in its formulated surfaces.

“The dust from its breakdown not only blackens the surface but has a negative effect on the environment. We think it is positive to work with experts for surfaces that give the best results for horse and rider.”

You may also be interested in…

Equine asthma (also known as IAD/RAO/COPD/heaves): how to help your horse

Arena surfaces: which is the right one for you and your horse?

We take a look at the types of arena surfaces available and which could suit your needs the best

‘Toxic’ arena surfaces could put riders and horses at risk

The Environment Agency is cracking down on the ‘illegal’ use of a substance as an alternative for equestrian arena surfaces

Would you give up prize money for a better warm-up surface? [H&H VIP]

Study shows maintenence of surface is key

Impact of riding surfaces on soundness

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Unlike the heart, or other muscles, equine lung function does not improve with training. This means that a horse’s breathing — his respiratory system — is always a limiting factor in his performance.

Equine asthma (EA), in a mild to moderate form, can compromise lung function and, in turn, affect athletic capacity.

The condition causes airway inflammation and mucus accumulation, which increases the resistance to airflow in the horse’s lungs. As a result, less air is inhaled with each breath and more energy is used to move the muscles of the chest. This impairs the exchange of oxygen and carbon dioxide — meaning that less oxygen-rich blood is delivered to the muscles to power the body during hard or fast exercise.

The more severe the airway inflammation, the greater the reduction in performance. Its significance will also depend on activity, because muscles demand less oxygen for lower intensity exercise.

Up to 80% of thoroughbred racehorses have airway cytology (the study of cells) evidence of mild-moderate EA, with increasing inflammatory cell numbers associated with reduced racing speed. The number of stabled sport horses affected may be even higher, although the association with athletic function is less clear and more individual.

As many as three-quarters of horses presented for high-speed treadmill investigation of poor performance have EA in its mild-moderate form.

Subtle signs

Aside from performance issues, there may be little obvious evidence of mild-moderate EA.

Most of the increased mucus transported up the trachea (windpipe) is swallowed, so only a small amount may be coughed up or appear as nasal discharge. Fewer than half of horses affected display a chronic intermittent cough, which is more common at the beginning of exercise.

Any signs of increased respiratory effort at rest would suggest the presence of severe EA. An exaggerated breathing effort during exercise may be apparent, however, or a prolonged increased breathing rate afterwards.

One prominent feature of mild-moderate EA is airway hyper-responsiveness — the development of bronchoconstriction (narrowed airways) and a cough during exposure to an allergenic environment, which in a normal horse would have no effect. The condition most commonly occurs in a stable setting, although a summer version also exists.

Typically, clinical signs will have been present for at least four weeks. A more variable history can also occur, however, with spontaneous improvement and worsening that reflects variation in environmental stimuli. Physical examination and bloodwork should be carried out to exclude any evidence of systemic infection.

The main diagnostic test for human asthma is forced exhalation — known as peak flow. After taking a deep breath in, you blow as fast as you can into a peak flow meter. This is repeated frequently and the results are interpreted based upon your age, gender and height.

With horses, it is impossible to confirm a diagnosis of mild-moderate EA using peak flow measurement outside of a research environment. Instead, a two-stage approach is used: airway endoscopy, to visualise and grade tracheal mucus, followed by fluid sampling from the trachea (a tracheal wash) or the lower airways (bronchoalveolar lavage).

Healthy horses have either no visible mucus and are graded 0/5, or only a few isolated specks and are graded 1/5. Poor performance can occur with a tracheal mucus score of 2/5 in racehorses and 3/5 in sport horses.

The fluid from the tracheal wash or bronchoalveolar lavage is then analysed for specific inflammatory cells, namely neutrophils, eosinophils and mast cells. In mild-moderate EA, bronchoalveolar lavage is the recommended sample: a neutrophil percentage of more than 6% in racehorses or 10% in sport horses is sufficient to affect performance.

Positive prognosis

Medical treatment revolves around control of airway inflammation using corticosteroid anti-inflammatory drugs. Alongside this, environmental modification is essential. Giving the horse corticosteroid therapy while keeping him in a dusty atmosphere will lead to improved clinical signs and lung function, but airway inflammation will persist and clinical disease will recur at the end of treatment.

In mild-moderate EA there is little bronchoconstriction at rest, so the routine use of bronchodilators (medicines to make breathing easier) is typically not necessary — although they may contribute to improved exercise tolerance during the early stages of corticosteroid treatment.

The most suitable treatment will be based upon clinical signs, exercise tolerance and the results of airway endoscopy and airway fluid sampling. The efficacy of this plan should be monitored by repeat airway fluid sampling, at a suitable interval.

The prognosis is excellent with appropriate treatment and a low-dust environment, since airway remodelling (structural change) does not seem to be a component of the condition. Mild moderate asthma is a reversible condition, but can recur if exposure to allergens recurs. However, progression to severe EA has not been shown.

Ref Horse & Hound; 26 September 2019

Rick Farr of Farr & Pursey Equine Vets shares his expert advice on Chronic Obstructive Pulmonary Disease, or equine asthma, how to manage it and what you can expect

Q: My gelding has been diagnosed with COPD (Chronic Obstructive Pulmonary Disease) at 15 years old. We showjump up to 1m/1.05m and obviously I am concerned at the affect the COPD will have on our competing. Does anyone have a horse with COPD, how do you manage it, how debilitating is it, do horses go back to full work and do they eventually find they have to have a slower pace of life?

A: It is strange how things move on within the veterinary industry and how we describe various conditions. COPD, or Chronic Obstructive Pulmonary Disease, was the term historically used to describe a condition in horses which was characterised by an increased respiratory effort as a result of allergic airway disease. However, COPD is actually a condition described within human medicine as a result of chronic smoking.

Over time, we as vets we started to use the term RAO, or Recurrent Airway Obstruction, but again, this terminology was not ideal. Now we describe the old COPD/RAO cases as Equine Asthma which, when put in context, is much easier to understand as most people are aware of asthma in people. Therefore, from this point on, I will refer to the condition as such.

Continued below…

Related articles:

• H&H forum: find out what H&H readers suggested
• How to recognise, avoid and manage respiratory problems
• Vets warn: rise in equine breathing problems

In both people and horses, asthma is a managed condition and should not prevent an individual from having a ‘normal’ life. The differences arise as a result of the severity of the condition within the individual and how responsive they are to medication, in conjunction with environmental management.

In the UK the prevalence of Equine Asthma is reported to be approximately 14%. Furthermore, there are suggestions that there is an increased risk of the condition in animals over four years old, Thoroughbred breeds, horse residing in urbanised areas and those that have been exposed to hay/straw in early life.

So, how is it diagnosed?

The best way to confirm the lower airway inflammation causing the condition is to perform two tests: a tracheal wash (fluid/sample taken from the trachea) and a broncheoalveolar lavage (a sample from the lung). The samples are then sent to the lab for analysis.

How do you treat the condition?

It is important to try to prevent exposure to certain causal factors, such as dusty hay/bedding. Horses should be kept in well ventilated stables. Very much like human asthma, some individuals are also worse when the weather is hot/humid or when pollen levels are high, therefore avoiding putting horses into these conditions can help. Environmental management is essential in all cases. Medication is also used to help — oral bronchodilators (drugs to open up the airways) in conjunction with steroids should be the basis for initial treatment. Often we progress onto treatment with inhaled medication, very much like in human medicine. This can either be administered via an inhaler or nebuliser.

You asked if the condition is debilitating. Initial management and control can always be a challenge, however medication with environmental changes can make sure your horse does not have to slow down. You do have to be aware though that, when competing under certain governing bodies, you may be required to check if any of the medications are on the prohibited substances list; this may affect your horse’s ability to compete in the future.

Once you have your diagnosis, getting the horse stable and managing the condition can take some time. However, once done, it is essential to monitor the response to any changes made. Some months the condition may be worse and require “tweaks” to the management — the condition will not disappear over night. With all this said, however, you should not be putting your horse in retirement just yet!

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Veterinary scientists are calling for the term “equine asthma” to be used to describe breathing ailments in horses, which are now among the most common veterinary problems.

In the May issue of Equine Veterinary Education, Canadian professor Jean-Pierre Lavoie wrote an article titled: “Is the time primed for equine asthma?”

He argues that the complex and evolving terminology that has been used to describe inflammatory syndromes affecting the lower airways of horses “has led to confusion for veterinarians and clients alike”.

Prof Lavoie said evidence has emerged recently to show that inflammatory airway disease (IAD) and heaves in horses “share striking similarities with human asthma”.

The professor puts forward the case that “equine asthma” should be used to describe chronic, non-infectious lower airway conditions currently known as IAD and heaves or RAO (recurrent airway obstruction).

The terminology would both improve “communication with clients” and would also provide “a wide umbrella, which remains appropriate as the diversity of the disease manifestations (phenotypes) and underlying immunological processes emerge in the future,” he added.

In the article he charts the many terminologies used to describe breathing problems in horses, from “heaves” or “broken wind” — which has been used for more than 30 years — to new terms introduced following recent research, such as “tracheal IAD”and “summer pasture associated pulmonary disease”.

The term equine asthma “allows for both flexibility and consistency over time, as some terms fall out of favour” said Prof Lavoie.

Cases of horses prone to breathing problems in the summer are likely to rise this week as temperatures soar to the high eighties in parts of the south, and forecasters are warning of “very high” pollen counts.

H&H vet Karen Coumbe added: “We have seen several cases of horses with non-infectious respiratory disease recently. A large number can be controlled with changes in management to minimise exposure to the common allergens such as dust, moulds, fungal spores or pollen.”

How to manage respiratory problems

* Horses with respiratory disease benefit from minimal dust environments

* Turn out as much as possible and avoid hay and straw, unless horses are allergic to pollen, in which case turn-out will not help

* If stabled, make sure stables are well ventilated with good air flow

* Soak or steam hay thoroughly or consider using haylage

* Choose dust free bedding, ideally for all horses using the same airspace

* Feed from the floor

* Keep the muck heap as far away as possible from stable and keep the affected horse out when you muck out

Ref: Horse & Hound; 9 July 2015

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