Hello, my name is Alicia Long, and today I'll be talking with you all about equine asthma, doing a little bit of review of the condition and sort of what we know about it, and an update on some of the more recent research that's been being done, and, and what you'll kind of see is that we still have a lot of questions to answer for sure. So, definitely continued research is gonna be, gonna be going on. So, like I said, we'll talk a little bit about defining equine asthma and differentiating mild from severe asthma, knowing the kind of available, and recommended diagnostics for asthma, how, the summer pasture associated severe equine asthma differs from other types, and then we'll go into some of the important management recommendations as well as treatment, medication options for equine asthma.

And at the end we'll talk a little bit about what we are learning about the equine microbiome of the respiratory tract and horses with and without asthma, and also some of the information that we're discovering about the possible genetic risk factors for equine asthma. So, first of all, the, the terminology, equine asthma, is, you know, certainly something that has gone through a lot of name changes, as many of us know, but currently the terminology that's being used is equine asthma with two sort of subcategories of mild to moderate equine asthma and severe equine asthma. So equine asthma again, as we know, was previously referred to as heaves and mild to moderate asthma is what we used to refer to as inflammatory airway disease or IAD and severe equine asthma previously called RAO or recurrent airway obstruction.

So, one of the reasons these name changes came about is, because, we have found, you know, a relatively amount of similarities between the, equine condition and the human condition, and, so therefore, this terminology was to try to kind of link those two as well as, you know, allow for sort of a better understanding of owners and veterinarians of sort of what these conditions really mean. And like I mentioned before, a lot of this is still sort of undergoing a lot of investigation as far as is there may be even additional sort of subcategories that we need to define and and identify to allow for sort of better diagnosis and and management of these cases. So it's, it's possible and likely that some of these terminology will continue to evolve and and add to some of our confusion.

So, when we talk about, you know, some of the, the definitions of these two different clinical subtypes, looking at the clinical picture, mild to moderate, equine asthma tends to be in young to middle aged horses, although it can be any age. The main thing that will be seen is poor performance. Especially in high performing horses.

Some sometimes horses can have coffee and a nasal discharge, although they don't have to, to have this form, and most importantly remembering that these horses don't have any signs, at rest, which is different from the severe asthma. So, also in their history will be, you know, some sort of, exposure, dust or allergen, namely being in a stable environment for, you know, some or all of their, their time, and, you know, the, condition can improve spontaneously on its own, or often improves if the horse is rested from exercise, which again is not necessarily an an option for all horses, right, if they have a job to do, the condition luckily is unlikely to recur once it's sort of controlled. Horses with mild asthma don't necessarily progress to severe asthma.

That's not, you know, that all of them will progress, but there has been some evidence that horses with mild asthma who show coughing or nasal discharge may be more likely to develop severe asthma. So that's something. No kind of when when examining these horses, you know, again, like I mentioned, likely in the future there will be sort of further dis distinction of this mild to motic category and even other kind of categories to allow for, you know, sort of more appropriate kind of distinction and and control of these cases.

And for the severe or including the summer pasture associated cases, these forces are usually older, so usually older than 7 years. They exhibit regular to frequent coughing, exercise intolerance to some level, not just poor performance. And one of the main features is again, they will have this increased respiratory effort and and signs.

Rest. So without, without exercise. They also, you know, will have a history of a dust or allergen exposure.

So, you know, for most cases being stabled, especially in the winter is when the time where these, you know, kind of fur smart start showing signs or for the summer past associated phenotype if the horse is out on pasture. That's when they're assigned to be the most. So again, summer or fall.

These cases can have a varying severity over time. They can go into remission in some cases, again, especially when they're, you know, less exposed to some of those allergens, and this condition really does often limit activity, you know, so especially exercise, but even other kind of lower levels of activity. This condition can be controlled with strict management, and treatment, but it's important to remember and remind owners that this disease is never cured, so it's never something that's gonna go away and, you know, management does become lifelong.

There is some increased evidence of some, oh sorry, we'll go into some of these clinical scoring things first. So, there have been some work to try to do some clinical, you know, kind of more objective scoring measures and horses, and a lot of these are based on kind of history, information from the owners as well as clinical examination. So this is, for instance, a questionnaire that it can be used with the owners to try to, you know, figure out some of these historical and clinical pictures and then be used to, you know, try to identify horses that are more mild or more severe in cases.

It's important to note that for all of these, kind of clinical, scoring systems that they have not been, you know, kind of, compared or. Some of them are not compared to other diagnostic types of, diagnosis of asthma. And so, you know, they're not gonna be kind of a replacement for those standard diagnostics.

But in this case here, by RAMs here at all, you can see this owner questionnaire, that goes into, you know, the history of the horse as far as, you know, have they had any coughing, nasal discharge, abnormal breathing, and then, you know, when does the signs occur, do they get turned out, you know, what is their, bedding type, what are they fed, things like that. And then the authors used this questionnaire to develop a scoring system called this horsey scoring system, but again this specific one was not compared to any sort of other diagnostics, and so while it can kind of group horses into, you know, whether they have no signs or, you know, moderate, severe or mild signs, this is not, you know, it has not been validated by comparing to other diagnostics of of equine asthma. There are a few scoring systems of clinical, you know, and historical signs that have been compared to lung function testing and and mucus scores and things like that that have shown, you know, some more kind of objective relation between the two.

So for instance, this one here, which is a 23 point scoring system, that, you know, goes through, you know, clinical examination that a veterinarian would perform on a horse or an episode and and uses them to try to grade them into mild to severe, . What's important to note and, and, you know, this scoring system as well as this next one here that looks mostly at kind of abdominal component of breathing as well as, you know, the nostril component and it's a little bit more simplified and, and, you know, trying to categorise these horses is that in these cases, these clinical systems are really not sensitive enough to differentiate mild cases of of asthma from normal horses, so certainly those horses could be missed and also . Will not be as significantly helpful in, you know, horses who have severe asthma, who might be kind of in remission.

So again, it's, you know, important to note that these should be used for scoring when the horse is having an an active episode. So then when we talk about again some of the, you know, kind of more diagnostic tools that we have available, we'll go through, you know, kind of the the baseline of, of diagnosis for asthma that we have available . And you know, again, there has been, you know, some variation between these and that not all of these diagnostics have necessarily strong association with each other or necessarily strong association between, you know, positive findings on the diagnostic and poor performance, and so there are definitely still a lot of questions to be answered, .

As far as, you know, how, how we sort of, you know, diagnose these cases. But for now, this is, this is the current recommendation and, and what we have available to us. So what's important to start out with is that, there, you rule out other causes of poor performance in these cases of mild to moderate asthma, you know, so upper airway things, cardiac, you know, lameness, musculoskeletal, neurologic, all of that need to be ruled out.

And for severe asthma, it's really important to rule out other causes of, of significant lower airway disease, you know, namely infectious causes, so those are important as well, and there, there is sort of an, a bit of an increasing evidence of a link between asthma and infectious agents, especially fungal agents, and so, you know, history, knowing the history that there have been any past infections, even if not active is important. So in these cases, you know, both would be using airway endoscopy to look for excess mucus in the tracheobronchial tree and there's, you know, scoring systems that will go into for BAL cytology. This is for mild to moderate cases, again, you'll have sort of more mild increases in neutrophils, eosinophils, or metachromatic or, you know, mass cells, and then in severe asthma, you will see moderate to severe increases in neutrophils, especially, is the key feature.

Lung function testing is, is an option, although, you know, not necessarily routinely used, but what we're looking for is airway hyper responsiveness, and In both cases, in mild to moderate asthma, there will be no airflow limitation with esophageal balloon dilation technique. And in severe asthma, there's moderate to severe air flow limitation, so kind of a significant effect seen there, that will be able to be reversed with bronchodilator administration. And another kind of important thing to, you know, discuss with owners is that there are some evidence of a possible genetic risk for development of, of asthma, especially severe asthma, which we'll talk about a little bit later, but it's important to discuss with owners, you know, if there's any sort of known history of parentage and, and any, you know, occurrence of asthma in, you know, fires or dams.

So now we'll go through each of the kind of key diagnostic tests that we have available and and a little bit about what we're looking for. So, endoscopy, you know, allows for again visualisation of the trachea and the presence of mucus. There are multiple different scales that are used, but .

In the sort of most recent consensus statement, they recommend this 5 grade scale, with 0 being no mucus, all the way up to 5 with profuse amounts of mucus. Healthy horses can have a grade 0 or 1. So, you know, a little bit of mucus is not necessarily indicative of asthma.

So for, these, you know, endoscopy grades, there definitely has been shown to be an association between, you know, the presence of mucus and, you know, poor performance in thoroughbreds, especially as well as some. Other types of sport horses, but there isn't always a great association in studies between the mucus scores and BAL cytology, and so definitely still some, you know, some questions as far as how those two relate to each other and, and kind of characterising these, these horses. And so here's some images that show examples of of each of these grades.

You can see again the trachea with no mucus, you know, there's kind of really nothing there, maybe like a little little tiny blob, and then all the way up to grade 5, which is sort of this, you know, extreme profuse kind of just huge pool of mucus at the bottom of the of the trachea there. And when doing endoscopy on these horses, it's important to remember to also do upper airway endoscopy at the at the time to, you know, rule out any other possible causes of poor performance, you know, such as displacement of the soft palate, things like that. So, important to do that as well as looking at the trachea for the presence or absence and and severity of mucus formation.

So, the next, you know, diagnostic tool that we have available would be BAL and here in this chart, adapted from the consensus statement shows the different cytologic features that we can see with normal horses or horses with asthma. So normal horses should have, you know, a very low level of nucleated cells, with a low proportion of neutrophils, eosinophils, and mast cells or metachromatic cells. Mild to moderate equine asthma can have, you know, some increases in neutrophils or mast cells or eosinophils.

Usually you'll see sort of one type increase predominantly versus others, but you can certainly have a combination. And then severe equine asthma has, you know, the significant increase in neutrophils above 25% and also correspondingly decreased lymphocyte and alveolar macrophage counts. So you'll notice when looking at the normal to the mild to moderate asthma categories that there is this kind of zone in between, you know, this grey zone and you know, that could be, horses who, you know, do have some mild asthma and just have lower counts, or it could be sort of a variation of normal, you know, for, for those horses, and so that can be a tricky, you know, kind of count to get is somewhere in that grey zone there and and then that relies on sort of ruling out other conditions and the other findings of the diagnostics for asthma.

It's also important to remember that the amount of volume infused in a BAL can affect the cell percentages. So, most references recommend a volume of 250 mLs of saline that's injected and then aspirated or suctioned back out. The definitions that we have are most often based on this amount, this one here in particular, as well as using a 500 cell differential.

Certainly other volumes are used and you know, you'll see maybe up to 500 mLs, things like that, but that can dilute out your cell population and, you know, affect that percentage that you get and so it's important to remember that when doing the procedure. BAL can be performed using an endoscope, and if this is done, this allows for assessment of the tracheal mucus kind of and the airways at the same time as fluid collection, and so that can be kind of a helpful feature. It does, you know, require a little bit of a different sort of setup as far as, you know, suction and aspirating, but can certainly be useful.

But also, you know, using a BAL. Specific, tubing and doing blind collection is also very reasonable to, to use as an option for performing this. If using an endoscope, it's important to use, you know, at least a 2 metre length, endoscope and the BAL tubing, to use a 3-meter length tube to make sure that you're getting, you know, down to those lower airways when you're collecting your sample.

There's definitely been some more recent evidence that has shown that for research purposes, you know, it's important to sample both lungs if possible, because there can be slight differences, you know, one lung to the other and so sort of pooling both of those samples would provide, you know, potentially a more kind of global and accurate picture of of what's going on in the lung, but, you know, certainly for clinical cases and especially out in the field, one lung sampling, seems to be, you know, effective and appropriate. So here are just some representative cytologic images of some BAL fluid, and so you can see the alveolar macrophages, which are the resident immune cells in the lungs, and they're quite large, compared to some other cells, the mass cells or the, you know, metachromatic cells, that really intensely take up stain. And then eosinophils have that, you know, really pink appearance, and then you can see the neutrophils, which are much smaller than certainly the other cell types, and so these would be sort of the, the kind of key cells to be examining and and counting for percentages when doing a BAL.

So the one of the questions that's more recently come up is, you know, is transtracheal wash appropriate for, you know, diagnosing asthma, and this certainly has been looked at in the past and historically transtracheal wash has really been kind of considered inappropriate for the diagnosis of equine asthma. You know, several studies showed a lack of agreement with BAL, and lack of association with poor performance or clinical signs, in a few studies when using trans tracheal wash. However, a more recent, larger study actually found a bit better agreement between, trans tracheal wash cytology and and other multiple other diagnostics for asthma.

And so, you know, there's been a little bit of kind of a rethinking of whether we can use this as a diagnostic tool and in the field transtracheal wash is, is likely, you know, to be appropriate for diagnosis of equine asthma, especially since it also allows for concurrent bacterial culture, you know, if you're kind of trying to in one time try to rule out, you know, sort of an infectious disease, and then also get the BAA ytology. So, you know, transtracheal washes, could likely be considered appropriate for diagnostic, which is a little bit different than kind of what was historically recommended. If for any reason mass cell phenotypes are suspected, trans trachea was should not be appropriate since mast cells are really pretty rare in the trachea and so it would be unlikely to be to be assessed, but this is a little bit of a more rare form of of asthma, but it is a possible cause.

So just to kind of briefly touch on lung function testing in human medicine, lung function testing is is considered the the gold standard to identify variability in pulmonary function. And especially if performed concurrently with bronchop provocation with histamine administration or bronchodilation with inhaled bronchodilators, and so, you know, certainly this would be the ideal and in equine asthma to use this in conjunction with other tests to, to confirm a diagnosis. But unfortunately, there is still no easily used system for lung function testing, for field diagnosis in horses, although work is being done to develop such a system and so unfortunately these, you know, kind of, setups are relatively complex and, you know, not easily sort of administered in the field.

And so currently, lung function testing use in horses really does remain limited to clinical cases that, you know, sort of select referral institutions or for research, although hopefully, you know, in the future this will change and allow us to to more accurately and, and, you know, reliably diagnose asthma if if this could be performed in the field in the future. So briefly just to touch on summer pasture associated severe equine asthma, which is, you know, a separate sort of condition. This is seen as asthma episodes in horses that are grazing pasture in the summer, in hot, humid climates, such as the US, you know, south, eastern US especially, or in the UK.

This is more seen in horses that are out on pasture and hot, dry weather, especially during harvesting. Or burning of crops, when that is going on in in adjacent areas. And so again, this is definitely different than the more typical asthma that we think of where horses are triggered by being in a stall with high levels of dust and allergens.

And this condition also has an adult onset, so similar to the other forms of severe equine asthma. Again, because of when the, you know, pathogens or, or the allergens are around, these asthma episodes usually will begin in the summer, you know, when those allergens are at highest levels and persist until the temperature or humidity decrease kind of sometime in the in the late fall. Significant improvement, it's really quite astounding, can be seen within hours to days of removal from pasture.

So placing these horses in a stall environment, or, you know, in really severe cases sometimes place them in a, you know, AC climate controlled environment can significantly alleviate to kind of resolve their symptoms even without administration of medications. Grass pollen is, is the suspected trigger for these cases. There's been various different types of grass that, have shown to be, you know, potentially more implicated, and then, there also is a possible fungal, trigger component, with fungal spores being implicated, especially as relate to, you know, various, grass and, and fungal kind of combinations.

This unfortunately is, is definitely a chronic progressive disease. You know, it, it really does tend to get worse with time, unfortunately. So environmental management is really key, which can also be tricky because again, you know, the, the recommendation is really no turnout for these horses during these times of year.

And unfortunately medications over time will often lose efficacy and that's why particularly in these summer pasture associated cases that environmental management is is really very important. So we'll transition into talking, you know, a little bit and kind of reviewing the management of equine asthma, which really the, the kind of, you know, key for management, is that, you know, the environmental control is, is extremely important, and then in combination with some of the pharmacologic agents that we have to, to intervene, is also really key, but it's important to stress to owners that this environmental management. Is is vital and especially in cases of severe asthma that, you know, these changes are going to need to be lifelong and so it's not gonna be something that you can change it and then, you know, once the horse is looking better, stop doing it.

It's, it's something they really need to do year after year and that can definitely get, you know, tricky for some owners and and can be a real hindrance. So having that discussion with them is is extremely important. So with our environmental management, the goal is to reduce as much as possible exposure to dust and allergens.

Unfortunately, as we all know, it's going to be unlikely that you can totally eliminate exposure, right, based on where our horses live and and how they're managed, but the goal is to reduce it as much as possible, so. You know, as we all know, for horses that are have the more typical equine asthma, reducing the time that the horse is in a stall whenever possible, so turnout on pasture is ideal. Again, this would be the exact opposite for horses with summer pasture associated type severe asthma.

Also improving stall and barn ventilation is really key, so, you know, whenever possible having sort of doors open, you know, windows with good ventilation, you know, horses that have asthma can be placed in the stall at the end of the barn, so closest to the door is a is a common management strategy. Stressing to owners to remove horses from the barn when cleaning the stalls, the aisleways, so when walking out the stalls, when vacuuming aisleways, and spraying down aisleways, all of these, you know, things, will increase the respirable allergens and and exposure to those allergens, and so having a horse in the barn when this happens can really, you know, worsen and and trigger their asthma. Discussing with the owners, you know, how they're storing their hay or bedding and so making sure that the hay or bedding is not stored, especially above the stall of a horse with asthma that it could kind of allow allergens to to kind of get knocked down into the stall or, you know, don't put them in the stall right next to where the hay or bedding.

Is stored, feeding hay on the ground is definitely shown to be in multiple studies important for these horses, feeding in a hay or hay net or hay rack, kind of increases the, respirable particles that these horses are exposed to. And this also is important to remember. When trailering horses that, you know, horses with asthma should really not have a hay net or or hayba kind of when they're getting trailered cause that will again just increase the exposure to those allergens that can really trigger their their condition.

Ensuring good quality hay, you know, not having mouldy hay is, is certainly a key, key strategy. Some studies have shown that, you know, recommending, the late harvest second cutting hay, can be useful as far as that seems to more consistently have some of the least amount of allergens, again, storing it in a very dry environment, making sure it doesn't become mouldy, even if it starts out a good quality. And then, you know, steaming and soaking hay is certainly something that you know, we all have have heard of and discussed and steaming hay is is a really attractive option as far as it can be, although expensive to buy the unit can be relatively easy to manage for owners, more so than soaking hay, especially in the winter, when these horses are often having their most significant signs, and so there aren't specific studies that definitively prove that steaming hay is, is, you know, better than soaking hay.

But at the same time, certainly is an attractive option for many reasons. If hay is soaked, it should be soaked for 30 minutes seems to be the ideal length of time, no longer because if it's any longer, then it can, you know, build up mould and and fungus and things like that, and reminding owners that when they feed it to remove it from the water again, so that the hay doesn't continue to soak for longer and and get mouldy. Again, this can definitely be something that's really tricky in winters for owners to do.

So having these conversations about how that specific owner is going to manage this strategy is really important for owner compliance in my, in my experience. Other options that are recommended and, you know, can either both be sort of not feasible for owners or maybe easier for some owners is switching horses to an all pelleted feed, or, you know, good quality haulage, which certainly in in the US haulage is fed less often than in some other countries, but pelleted feed is, you know, really important for, you know, reducing dust. And so if an owner is able to feed only hay pellets and, you know, keep the horse at sort of a good body condition and, and meet their caloric needs, especially if they're a performance horse, that's something that some owners would choose to do over having to soak or or steam hay, so something to consider.

Again, Hermiing owners to choose low dust bedding options, and you know, that can vary based on kind of their source of the betting between different types of betting, so it can be a little bit different for every scenario. Really straw should not be recommended, for these horses, you know, technically if you have really, really good quality straw, and then maybe that will have, you know, be a reasonable option, but Unfortunately that's uncommon that you find that really good quality and so because straw has such high levels of allergens and toxins, it's really recommended, you know, to, to not have owners bed these horses and that and honestly, ideally not at all in the barn, you know, so ideally the bedding would be low dust for for all horses so that, you know, the barn environment is less allergen, but particularly for whatever stall this specific horse is in. So, then moving on to, you know, one of our other mainstays of management for these cases is, you know, therapies, so specific pharmacologic therapies.

And so, corticosteroids are certainly a mainstay of treatment for these cases, and, you know, have been shown to have significant success. Again, important to remind owners that corticosteroids alone are not going to be the best option for these hoes. It really needs to be combined with the environmental management.

There have been studies that show that corticosteroids can be Less effective if management strategies aren't also, you know, implemented, as well as they can sort of have less length of efficacy, so they can sort of lose their efficacy over time if the horses are still exposed to the same level of allergens that they were before you started the corticosteroids. So this is definitely something to stress with owners because obviously the medication administration could be easier than the management and so it's often something that they're, you know, looking for is that kind of magic bullet of the medication, but they really do need to be combined with each other. So systemic corticosteroids are certainly a very effective way to manage asthma.

They definitely show good success, but, it's important to remember the systemic side effects of systemic corticosteroids, one of the key things being, risk of laminitis, especially unfortunately a lot of our horses that we're managing for asthma, especially severe asthma, might also be metabolic, have, you know, you got metabolic syndrome or equine Cushing's and Then you would have to, you know, kind of weigh the risk and benefit of of systemic steroids, and so certainly metabolic testing in in horses that are middle age or older before considering systemic steroids would certainly be recommended to to try to know if they're dealing with those other conditions. Dexamethasone has, in multiple studies been shown to improve clinical signs, lung function, and mucus scores in severe equine asthma, so definitely a very effective treatment whether given IV IM, or oral. There is a bit of a less clear benefit of dexamethasone on BAL cytology and horses with asthma and so again, you know, that a little bit remains the question is why, but certainly, definitely really good clinical success with dexamethasone.

Prednisolone does not seem to be as effective as dexamethasone for equine asthma, in, in studies, and so while it certainly is an option and, and, you know, can have, can have effect, it seems like dexamethasone, even oral dexamethasone would be the superior choice specifically for asthma. Triamcinolone is something else that's mentioned as far as systemic triamcinolone administration for control of equine asthma and, you know, certainly, does show to have some effects, but again, the, the risk of side effects as well as the cost makes it a little bit more kind of limiting compared to dexamethasone. Interestingly, there was a relatively recent study that came out that demonstrated that horses with severe asthma who had intra-articular injections of triamcin alone actually had a improvement in their lung function for 3 weeks after their joint injections and so.

Interesting to kind of show that yes, triamcin alone is absorbed systemically when given into the joint and also that it might be absorbed at levels enough that can actually affect horses with asthma. So that's an interesting, kind of, side effect of that. Inhaled corticosteroids really sort of be the, you know, most promising option for treatment as far as the goal would be you could administer local therapy and have effects locally in the lungs, while trying to avoid the systemic effects of corticosteroids.

So these are certainly, you know, options that are that are intriguing. Unfortunately, studies have shown that dexamethasone nebulized is not very effective for controlling asthma, and at higher doses has does still have systemic absorption probably from horses sort of swallowing the medication during the nebulization. And so, you know, even though dexamethasone inhaled would be a attractive option for the fact that it's relatively inexpensive and easy to obtain, it seems like this is not something that should be recommended for inhaled, .

Medications, there are different ways to deliver inhale medications, so, nebulizer systems, metre dose inhalers, which is the sort of human puffers combined with the equine specific administration system, and then, this sort of single softness inhaler product that has just been released. So for the metre dose inhalers, the medications that we have available include blamethasone, fluticasone, and budesonide. All of these have been shown to have positive effects on lung function, and horses with asthma, so certainly do show effects.

Unfortunately all of them have some, although varying levels of systemic absorption, based on, you know, measurement of cortisol and horses, and so, you know, while they're less so absorbed systemically than just giving an IV or oral steroid, they unfortunately do have some level of systemic absorption, which could be detrimental in in certain at-risk courses such as those with metabolic disease. The soft mis inhaler, which is the loinide product, from a servo, has, definitely have some attractive features and that it's been shown to have similar improvement in lung function, to systemic dex methasone in horses with asthma, which is very promising and no apparent systemic absorption. So again, this is a, definitely a pretty attractive product for managing horses with asthma.

So the other kind of class of therapies that we can use for equine asthma or the bronchodilators, and these are really reminding kind of, you know, veterinarians and owners that these should be considered as sort of a third line of treatment. So they're really not, you know, a primary treatment method, environmental management and, you know, plus or minus corticosteroids is really the key, and then these can sort of provide support for those, but, in humans, there's actually been some studies that show. So that bronchodilator administration alone can have increased mortality risk in humans with asthma with severe asthma, as well as they can actually, if you think about it, if you don't make the environmental changes, bronchodilators could actually sort of worsen exposure to allergens because you're dilating those that bronchio system and while still having the same amount of exposure to the allergens.

So, certainly this is not something that should be done alone without other strategies. So, you know, when we discuss these with owners and, and kind of thinking about how to use them, they really should be sort of a short term, solution while the other strategies are implemented for more long term control, or, you know, in the case of inhaled, for kind of a rescue situation. So the main options that we have would be labuterol, so an oral systemic formulation.

That can provide bronchodilation. This does, as we know, have reduced efficacy over time, due to tachyphylaxis where there is decreased availability of the receptors for the medication and so short term use is really recommended, you know, like in the week time frame, to avoid, you know, kind of, decrease efficacy, with its continued administration. There is a little bit of certainly a delayed onset of action, you know, and so it's not really for rescue therapy and a horse is having an active crisis.

This would not be sort of an effective mechanism. Some of the side effects, can, that can be seen, although not in every case, includes sweating, tachycardia, and anxiety, and so especially when using it at higher doses, something that should be watched out for. The main inhaled bronchodilator option that we have is albuterol.

It does certainly have a very quick onset, you know, less than 5 minutes, and so this can be used in a rescue scenario in a horse that's really having a crisis. It does definitely have a short duration of action, you know, no more than an hour, which is even shorter than in humans, and so, you know, definitely not effective for any sort of longer term control. It's recommended with this product to use the multi-dose inhaler, the puffer, with an approved equine delivery system, you know, that's designed specifically for horses for the best effect, because, you know, other administration methods have been shown to maybe be less effective.

So here are just some, you know, kind of reviews of some of the dosage and frequency administration for our systemic medications, namely dexamethasone, prednisolone and conbuterol, certainly a wide ray of doses that can be used and a little bit depending on sort of the severity of the clinical signs at the time that the medications are started. And then for inhaled medications, we again have the corticosteroid options with cyclloinide being the newer product, that's the proprietary administration system and then our inhaled albuterol for the, for the bronchodilator. So there definitely are a few other, you know, therapies that are mentioned for equine asthma and even more than, you know, I'll discuss here, but, mainly the dietary fatty acids or the omega 3 fatty acids have been discussed in a few different studies as far as potentially helping improve you know, clinical signs and response to treatment in these cases, .

The way that these would work is by decreasing the substrate available that produces the pro-inflammatory eoinidesosonoids, and the inflammatory cytokines. And so, you know, trying to help decrease the inflammation, the inflammatory response in these horses, the most effect on. Has been shown when these omega 3 products are combined with a switch to paled only diet and given sort of long term.

And so, you know, sort of giving these omega 3s kind of, you know, here or there or without changing other factors is probably less effective, but certainly something that can be considered and and recommended for owners to to use in these cases. Definitely lots of other things that have been evaluated, especially for inhaled therapies besides, corticosteroids and bronchodilators to try to help improve the clinical picture in these cases, but, specifically there is no evidence or data to support the use of inhaled eucalytic or muokinetic agents such as acetylcysteine, which certainly has been tried before, and so these are unlikely to to be a necessary or or helpful addition to the treatment protocol for these cases. So a little bit I wanna touch on, you know, some of the other kind of investigations that have been done and are being currently worked on in asthma to try to identify, you know, other underlying causes of the disease and, and try to allow us to have better ways that we might manage these horses and provide, you know, additional interventions to help improve outcomes.

So the respiratory microbiome has been you know, some descriptive studies have been done to look at the microbiome and both healthy horses and horses with asthma, and, you know, what we found in, in healthy horses is that, there certainly is a, you know, a significant proportion of bacteria that live in both compartments of our airway and previously was thought of that the lungs were sort of a sterile environment, but we know that that isn't true. The lower airway definitely has lower bacterial species richness, so, you know, less kind of numbers of populations or different types of bacterial populations then found in the upper airway, which has a pretty robust and diverse, microbiome, but there is a large overlap in the bacteria that's present in the two locations, and so, you know, some support for the fact that there is kind of a congruent environment between the two and they do share some overlap in their in their bacterial populations. When looking at the microbiome in asthmatic horses, there, definitely has been shown to be a different lower respiratory microbiome in horses with mild asthma, as compared to healthy horses, significant differences in, in the, you know, bacteria present has been found as well as in Diversity numbers.

Interestingly, streptococcus species, increase the most in relative abundance in horses with mild asthma compared to, healthy horses. So, you know, potentially that could be a, a population of bacteria that can be investigated to try to allow for intervention. systemic and inhaled corticosteroids definitely affect the, lower respiratory tract microbiota in both healthy and mild asthma asthmatic courses.

So, you know, those medications are certainly have an effect on the microbiome and whether that effect is part of why they're helpful or is more of a detriment, is still to be elucidated for sure. Treatment with, systemic corticosteroids had more effect on the microbiota than environment in one study. So again, if, you know, we try to use these to think of why that might be, you know, maybe, environmental changes have the ability to, to decrease the the signs of asthma without changing the the normal healthy microbiome.

Possible, but again, these studies, like a lot of other microbiome studies and horses are still descriptive at this time, and so, you know, definitely further work needs to be done to try to figure out what is the causative role of changes in the in the microbiome on horses with asthma and and their disease and disease severity. Or is it more so that the microbiome is, is secondary to the asthma and not a causative factor, and then if it is a causative factor, you know, what can we do to try to intervene, related to the microbiome to try to help improve outcome in these horses, so. Definitely still, still a lot of unanswered questions that that will be continuing research for quite some time, I'm sure.

And then just to briefly touch on genetics and equine asthma, there's been a a really quite a large number of studies coming out looking at various genetic, you know, markers and different components of the genome and how they can be different in in horses with asthma and those without, and definitely there's pretty robust evidence for a genetic predisposition to severe asthma in several specific warm bloodlines and families, that's really where most of the work has been done is is in these warm blood families, . What we certainly have learned is that there is a very complex genetic basis and so multiple different, you know, genes and segments of genes have been have been found to be related between the horses with asthma and so still definitely, you know, really difficult at this point to isolate kind of the causal specific variants that you know are causing the signs. The interesting the chromosomal regions and the modes of inheritance, inheritance are not the same across the families that have identified in the various studies, and so what this tells us is that there is a definite level of genetic heterogeneicity, which basically means that depending on the genetic makeup of the specific horse, different genes might be conferring the susceptibility for equine asthma.

So, you know, I think that adds to a lot of the complexity of trying to identify the specific genes because it might be different genes and different horses, or different families that are that are causing these changes. Definitely another interesting thing is that genetic investigations have revealed some links between severe equine asthma, allergic skin disease, and intestinal parasite susceptibility. So, you know, there's definitely relation to the immune system and and kind of why these different conditions might come up in an individual horse and, you know, maybe some some further work will show us kind of how we can use this to identify horses at risk and also sort of manage manage these horses.

There's definitely less understanding of, genetic risk factors in mild equine asthma. You know, there's, there's sort of been some evidence of possible link and, and, you know, as you mentioned previously, the, the understanding that horses, you know, some horses will have cough and nasal discharge with mild asthma and others won't, and some of those horses might be more likely to go on to develop severe. Asthma, in the future as they age, so, you know, again, does that hint at some genetic, you know, link between horses that have that and horses that don't, it's possible, but again, definitely much less information in those cases.

So hopefully in the future, further additional genetic studies will allow us to identify, you know, horses that are going to be more at risk for asthma than others based on their their parentage and genetics. So, today we again talked about equine asthma and how we can differentiate the different, you know, forms of asthma, and how we can diagnose those, although knowing that definitely there's still a lot of work to be done and the best way to diagnose these horses both from an easy field perspective as well as, you know, really making sure that our diagnostics are agreeing with each other in in our diagnostic outcome. Talking about the difference between summer pasture associated severe equine asthma and how that presents differently as far as those forces really are triggered by being out on pasture, which is sort of the exact opposite of the other types, being able to, you know, talk about the management recommendations with owners that are really important for them.

To to follow through with and also our available treatment options, including both systemic and inhaled medications, and then a little bit discussing the respiratory microbiome and the current kind of understanding that we have of some of the genetic risk factors, although, still a lot to be explored that way. So some of the references we use, the main thing would be looking at the ACBM consensus statement on equine asthma, although likely to be revised in the next little bit here so thank you very much and hope you, hope you enjoyed.