The Latest on Equine Asthma

This article is from the January 2020 Horse Deals magazine.

With Dr Surita du Preez BVSc, DVStud, MANZCVS, DECEIM
Dr Surita du Preez completed her undergraduate veterinary degree at the University of Pretoria in South Africa in 2007 and shortly after moved to Australia where she took on roles in private equine practices. In 2017, Surita completed her residency training and doctorate at Charles Sturt University in Wagga Wagga, NSW. The following year, she became a boarded specialist through the European College of Equine Internal Medicine. Surita became a part of the University of Adelaide’s Equine Health and Performance Centre team in May 2018 as an Equine Medicine Clinician.

What is equine asthma?
Equine asthma is a reasonably new term. It was first suggested in 2016 as a catch-all term for two syndromes that have been treated and managed in horses for many years. The term describes both Inflammatory Airway Disease (IAD), and Recurrent Airway Obstruction (RAO or Heaves). Inflammatory Airway Disease is classified as mild to moderate equine asthma, and Recurrent Airway Obstruction more severe equine asthma. The overall term is not to say that horses with mild to moderate asthma will necessarily develop severe asthma, but there are a lot of similarities in the two which is why they are now under one name.

The majority of my research is about the mild to moderate form of asthma. This disease is poorly defined in what the cause is, but we know that it is associated with inhalation of respirable particles that stimulate inflammation in the respiratory system. Respirable particles are small particles that can make it down into the lungs; inorganic dust, bacteria or mould products, hay dust, or allergens and pollen. This form of asthma can affect horses of all ages and all breeds. It’s diagnosed quite commonly in young performance horses, such as racehorses, because it limits their ability to oxygenate, so to breathe well enough to perform at their peak. In really mildly affected horses they just can’t breathe enough to perform as well as they usually do. In performance horses, it can show as an unwillingness to go forward or engage so owners often have a complaint that their horse is lacking impulsion or just not working as well as they used to. As the disease progresses or becomes more severe, the horses might also cough or may have nasal discharge. The mild to moderate form doesn’t affect the horse’s wellbeing at rest, only when they have to exert themselves. From a welfare point of view, for untreated horses that are required to exert themselves, it would be perceived to have some detrimental effects.

When I speak about mild to moderate asthmatic horses coughing, I’m not talking about a horse that is persistently coughing. Horses generally don’t cough, they have a very poorly developed cough reflex, unlike humans who are very sensitive; if we just have a scratchy throat we might cough, but horses aren’t like that. Many people think it’s normal for a horse to cough once or twice when exercising but it’s not. They shouldn’t be coughing at all when they are working and it’s important that we get that message out there; if a horse is coughing it means that they have inflammation in their lungs, even if it’s just one cough.

With the severe form of equine asthma, it’s known that there is a genetic predisposition and that the main trigger is hay, hay dust, and fungal particles associated with hay. Those horses that are affected are usually older, at least seven years old. Again, it can be any breed, though some Warmblood lines have a genetic predisposition. A key difference between the mild to moderate form and severe asthma is that severely affected horses often have signs of respiratory distress at rest. They may have their nostrils flaring, have increased abdominal effort or they may be so affected that they overtly look like they are struggling to breathe. Severe asthma is pretty common in the UK and Europe and certain places in America, but anecdotally, between quite a lot of specialists in Australia, we seem to not see as many horses with the disease here.

How is asthma currently diagnosed?
If a horse presents to us that may be affected by asthma, we currently conduct a scope and bronchoalveolar lavage (BAL), commonly called a lung wash. First, we look at the horse’s upper airways to determine if there are any other issues which could be contributing, and then we look for and grade the amount of mucus in the trachea (windpipe). We may also take a sample of this mucus. Next is a lung wash, which is where we find the furthest part of the lung that the scope can fit into and infuse sterile saline and then take it back again. This washes the cells out off the air sacks (alveoli) for collection. The collected cells are analysed under a microscope and they can tell us a bit of a story; whether there is inflammation, and what type of inflammation.

What inspired your research into asthma?
When I moved to South Australia, I was struck by the high rates of asthma in people in the state. About one in seven South Australians are affected by asthma, which had me thinking that we should be seeing a whole lot of horses with asthma too. If there are triggers for people, it could be conceived that there are also triggers for horses. I had a few options for my doctorate but I have always enjoyed respiratory medicine.

What has the research involved?
The first part of the research was focused on evaluating the use of non-invasive methods to diagnose or at least evaluate lower airway health in horses, specifically horses with equine asthma. A major component is evaluating the use of exhaled breath condensate as a less invasive way to both diagnose asthma and monitor the horse’s response to treatment. Sampling exhaled breath condensate involves putting a mask over the horse’s nose and letting them breathe for 15 minutes. Then we collect their breath, which is essentially frozen. That breath is analysed to see if we can identify markers of inflammation. That research and testing showed that we can use exhaled breath condensate to diagnose asthma as there were increases in the pH and hydrogen peroxide levels in the breath of horses affected by asthma. We will be continuing to research and test this method before it can become a clinical tool.

In the meantime, we are also evaluating the process of the lung wash method (bronchoalveolar lavage (BAL)) to see what the gold standard should be for diagnosis. We’ve been using this technique since the 70s and the initial work suggested that we only needed to sample one side of the lung because the inflammation in horses with asthma is generally equal and affects the whole lung. Though there have been a few recent studies that have shown that if you only sample one side, you might miss the diagnosis in some horses. Therefore our research aim is to get more evidence to help us determine if we should be sampling both lungs (left and right sides) or just one side. Some ask why wouldn’t we just do both sides and it’s a monetary issue. Every time we sample something it has to be sent to a lab and that costs the owner money, but the accuracy of the diagnosis is important, hence this research is still ongoing.

The second part of the research project is an Australian-wide survey, aimed at horse owners, that is hoped will give us more concrete evidence about how many horses may or may not be affected with respiratory disease, specifically asthma. When we receive the results back, there is a scoring system that, based on the answers received, will identify horses that are likely affected by asthma. This is essential to the Australian equine industry as currently the majority of the data we have is from overseas and we do not know how prevalent equine asthma is in Australia. The survey will also be utilised in determining why our population is affected by asthma differently to other populations.

For the horses that are diagnosed with asthma, what’s involved in its management?
The management part is one of the big areas where there is a lot of overlap between the mild to moderate and severe forms of asthma. We essentially manage them the same, but we have to be a lot stricter with horses with severe asthma. The cornerstone of the treatment is environmental and dietary management; to eliminate or at least reduce the number of particles that the horse is exposed to and therefore inhaling. Unfortunately in many parts of Australia, we can’t do anything about how dry and dusty the environment is. What we can control, at least, is the amount of dust and particles they are likely to inhale when eating.

For mild to moderate cases:
• Always feed at ground level. Gravity helps keep the particles out of the lungs. Don’t feed your hay in a hay net tied up at or above knee height.

• Either steam or submerge hay completely in water. Both of these methods increase the moisture in the hay and therefore reduce dust. When submerging hay, unlike soaking hay for a laminitic or horses affected by equine metabolic syndrome (EMS), the hay needs to be completely submerged into water and removed straight away and fed wet. If you are steaming, I recommend using a commercial steamer. Unfortunately, homemade steamers do not penetrate the hay as well.

• The type of hay bales you feed to your horses is also detrimental to their respiratory health. It’s not recommended to feed round bales to asthmatic horses. Round bales are exposed to the elements for a prolonged time and have a really high bacterial and fungal count within the hay already. Also, horses tend to ‘dig’ holes with their noses in the round bales and eat from the inside. When horses eat, they inhale most of the particles they are going to inhale within a day. If clients do still have round bales, I recommend hand feeding them, wetting the hay and allowing them to eat it at ground level.

For severe cases:
• For severe cases, we take the horses off of hay and feed them a complete pellet diet. They are so sensitive to the dust and allergens that they really shouldn’t be eating any hay.

• We also treat these horses with steroids, especially in acute instances. The preferred steroids are inhalable, administered through an MDI (metered dose inhaler), similar to the human puffer. Nebulisers can be used, but puffers are preferred as the particle sizes it generates are much smaller, and can penetrate the bottom part of the lung better. Puffers can be given to asthmatic horses by a mask (similar to the nebuliser) or you can use a spacer and cup that fits over one nostril. You administer the puffer into the spacer and wait for the horse to inhale two to three times and then repeat until you’ve given the full dose. In most cases, this needs to be done twice a day, especially initially (for the first four or so weeks). Most horses tolerate the treatment quite well and in a lot of cases, if we can eliminate the initial triggers, we can stop the treatment after six to eight weeks. Some horses will have recurrent episodes which will again require treatment.

What’s the likely outcome for asthmatic horses?
The severe form of asthma is a permanent disease through immune dysfunction, those horses develop remodelling of their airways. Horses with severe asthma need lifelong changes in management and treatment, or they eventually risk deteriorated pulmonary (lung) function. If they are managed and treated adequately they can live fruitful and well-performing lives.
The mild to moderate form of asthma is non-permanent and is an inflammatory response. Through the management and elimination of triggers, it is reversible and the horse’s lungs can return to normal function.
We feel that our equine asthma research will ultimately improve our understanding and our ability to manage our horses, and hopefully prevent the disease in the long term and increase awareness and improve horse welfare by improving their overall health.

Get involved
Dr Surita du Preez and her team have now rolled out the asthma research survey and would love your participation. The aim of the survey is to identify risk factors for the development of equine asthma so that relevant strategies can be implemented to prevent disease development and to introduce better management techniques for horses that are already affected. This survey will help to provide critical information to help improve the health and welfare of horses in Australia.

Horse Deals invites you to aid in the team's research by completing the short 10 to 15-minute survey. Simply follow the link: https://is.gd/EAsurvey

Your information will be treated confidentially, and you may choose to remain anonymous or you can provide your details to be entered into a prize draw. First prize is a $100 Kentucky Equine Research (KER) voucher, 2nd through 5th prizes are a $50 KER voucher. The next 50 draws will receive a voucher for their choice of a bag of Calm Performer or Complete Performer from Barastoc Horse Feeds. The survey closes on the 17th of April 2020.

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