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Why Does My Horse Cough?

The equine athlete and non-athlete are often plagued with a cough, which can inhibit quality of life and reduce performance. Coughing can be sporadic, changing in intensity as the environment changes, or it can be continuous, becoming worse or more prominent at the time of exertion as seen during competition.  Some coughs in horses get worse with certain seasons, becoming progressive over time. So, what makes a horse cough and what can we do about it?

A cough is a normal reflexive response by the body to rid the airways of dirt, debris, mucous, phlegm and even infectious material.  It is really a defensive mechanism by the body, with the end goal of keeping the airway clean for air movement and optimal oxygen exchange.  The airways have several components to them, each playing a vital role.

Basic Horse AirWay Anatomy

Horse Nasal Anatomy
Horse Nasal Anatomy
  1. External Nares: At the beginning of air travel, we have the external nares, which are present obviously on the end of the nose.  They open and close, increasing in size to accommodate various demands for air movement.  As the horse undergoes more exertion or is stressed due to respiratory disease or other health condition, the demand for air and oxygen increase, thus the nares will open more fully upon inhalation.  The horse is pretty much an obligate nasal breather, meaning they rarely will breathe through their mouths unless absolutely necessary in a critical condition.  This is mainly due to the arrangement of structures at the back of the throat region or pharynx.  So, at least initially, the horse’s nares need to be open and capable of moving air.  Any obstruction in this region may compromise the ability to breathe properly.
  2. Upper Airway or Nasal Passage:  The nasal passage is next in line and encassed within the skull, leading to the back of the throat.  In the nasal passage, we have both left and right passages, but also several folds of nasal concha, which divide the nasal passage into sections. The cocha really act to filter air, pulling out and accumulating debris which might be present, such as dust or dirt, but they also warm and moisturize the air.  Located in the same region is the maxillary sinus, which drains to the back of the throat along with the frontal sinus.
  3. Pharynx: This is the main structure at the back of the throat, basically the voice box region that you can feel in your own throat.  This structure is designed to channel air down into the lower airways, and it opens and closes dependent upon inspiration, expiration and even swallowing. When a horse eats, same as in humans, we do not want food going down the wrong ‘pipe’, so the pharynx closes up, helping to prevent aspiration of food into the airways and helps to direct food into the esophagus.  This is mainly why we can’t swallow and breathe at the same time.  Those that have tried this quickly realize that choking and coughing are quick to follow. The pharynx is also the main structure in which problems occur such as laryngeal hemi-plasia or dorsal displacement of the soft palate.
  4. Trachea:  The trachea or windpipe is next in line, receiving air from the upper airway and channeling it like a tube down to the lungs.  It is not common to have direct problems with the trachea, outside of overt trauma or injury.  In some cases, due to deformity, there can be a narrowing or stenosis to the trachea, which can create airflow problems.
  5. Lungs:  The lungs are the main organ, located within the chest and protected by the ribs where airflow ends and oxygen exchange begins.  The trachea join the lungs and divides into left and right main stem bronchi.  As the air moves into the bronchi, further down we divide into smaller tubes called bronchioli and then finally into small pocket like structures referred to as the aveolus, which is where oxygen is taken into small capillaries for the body to use and exchanged for carbon dioxide.  We breathe in oxygen, amongst other gases, which the body requires and we expel carbon dioxide, which the body does not need. It is this aveolus, small bronchioli region where EIPH or bleeding also occurs.

Seeing all of these working components to the airways, we can really have a problem in any location which may produce a cough. In reality, when we have problems such as obstruction or blockage or even an irritant in the upper airway, we will usually see a sneeze.  In comparison, when we have a problem in the lower airway, from pharynx down to the lungs, we more often see a cough.  The upper airways want to blow out a problem (sneeze) and the lower airways want to force up a problem (cough).

When we have a cough, it generally signals a problem in the lower airway, so this is our focus for discussion.

Diagnosing a Horse That Coughs:

Diagnosis of coughing or pulmonary conditions can be tricky at times and even complicated.  Some diagnostic tools that we may use as veterinarians include:

  1. Full physical exam with temperature and rebreathing bag to allow us to listen to the lungs better
  2. Bloodwork including chemistry panel and complete blood count
  3. Upper airway endoscopic examination to evaluate upper airway, including trachea to the point of bifurcation into bronchi
  4. Transtracheal lavage to obtain samples of fluid or mucous debris in upper airway for cytology and culture
  5. Bronchoalveolar lavage to obtain samples of fluid or mucous debris from bronchi and lower airways
  6. Ultrasound

Common Causes of Coughs in a Horse:

  1. Airway obstruction:  This includes dorsal displacement of soft palate, laryngeal hemiplasis (roarer), foreign object in the throat or lower airway, tumor or mass, or even trauma.
  2. Mucous or Phlegm production: This is one of the most common causes of a cough in a horse and often associated with allergies and/or infectious causes such as an upper or lower respiratory infection.  I say both upper and lower infections, because it is also common to have a horse with infectious sinusitis, which may then be draining to the back of the throat and even into the trachea or windpipe, creating an irritation, actually a partial blockage and the eliciting a cough by the horse to clear this debris.  Of course, we also have lower respiratory congestion with mucous and/or phlegm that may also create blockages, secondary to allergies or primary infectious causes. This is common in cases of COPD (Chronic obstructive pulmonary disease) or RAO (Recurrent airway obstruction)
  3. Bleeding/EIPH: Bleeding into the lung tissue as a result of EIPH is also a common cause of coughing, dependent on the degree of the bleed.  This cough is usually transient, short lived, but seen post exercise, persisting until the condition is stabilized.  In most of these cases, we will also see blood in the nares, but not always, which is due to the blood being moved up from the lung tissue into the trachea and finally draining forward.
  4. Inflammatory airway Disease (IAD): This condition is really not far removed from COPD or asthma in the horse.  In these cases, the airway is irritated, often being dry in nature as well, overly reacting to many things in the air which is being inhaled.  IAD cases differ from COPD cases, in my opinion, based on the degree of mucous production present.  In reality, in equine medicine, both IAD and COPD are considered asthma to varying degrees, thus being similar in mode of action and end result to the patient.  IAD cases tend to have a dry cough, little mucous production, while the COPD patients tend to have more obvious mucous present.
  5. Infectious Causes: Upper and lower airway infections are common in the horse.  The infections can be viral, bacterial or even fungal in nature, creating localized irritation and inflammation, thus eliciting a cough.  In most cases of infection, we also have mucous or phlegm production, as a defensive mechnism, and this mucous or phlegm can then also contribute to the cough.

The most common sources of cough really vary from one breed to another and also environment dependent.

In the TB racing industry, we commonly encounter upper airway problems that create physical obstructions, such as DDSP or roaring, but we also see more cases of inflammatory airway disease (IAD).  In the western disciplines, we more commonly see coughing related to COPD or in some IAD, with more mucous production and airway irritation, often made worse by dusty environments.  Of course, we can also have bleeding and infectious causes in all horses, which may be primary or secondary in occurrence, which implies that horses with IAD or COPD are actually more prone to bleeding and even infections, due to the already existing inflammmatory and immune response. In reality, the presence of IAD or COPD actually predisposes the patient to an increased likelihood of further problems, again due to a heightened level of inflammation present and often immune dysfunction.  Thus, we commonly see COPD patients or IAD patients have concurrent EIPH or bleeding, and those patients are also more likely to develop secondary airway infections.

We have to further define IAD and COPD and state that both of these conditions are really allergic responses, contributing to varying degrees of asthma in the patient.  IAD and COPD are different in some respects, but when we get down to the details, the cellular response is quite similar. Actually, many IAD patients can and do progress to become COPD patients over time, if that condition is not managed.

We also have to understand that most of these conditions, including IAD, COPD and EIPH all involve the inflammatory and immune response. Thus, all three conditions really are inflammatory in origin, thereby contributing to various cellular changes and responses in that patient, creating the syndrome or clinical signs we are seeing.  More often than not, all three are actually interconnected.  As an example, it has been noted in research that patients with EIPH actually have inflammatory airway changes, which includes IAD, COPD or prior chronic infections.  Chronic EIPH horses also are prone to developing inflammatory airway problems just due to the fact that the blood in the airway, not to mention inflammatory damage to blood vessels, creates a chronic inflammatory response in the airway itself.  This can then lead to narrowing, obstructions and really overall inflammatory airway disease on some level.

Management Options for Coughs in a Horse:

  1. Environment Control: This is mainly done to reduce the amount of dust that the horse is exposed to, which may include watering down hay, changing bedding type, watering down arenas or even changing the footing, or improving airflow in the barn or stall area, or plainly just letting that horse get ample pasture time in open air.
  2. Medications:  Pharmaceuticals are needed in some cases, especially if there is infection in which case antibiotics are warranted.  In other cases, if airways are closed up, some may utilize bronchodilator medications to open those airways, such as Clenbuterol.  These can be very helpful in severe cases of asthma where the horse is really having a hard time moving air at rest. Steroids, corticosteroids such as Dexamethasone, are also commonly used in cases of IAD or COPD, helping to modify the inflammatory response. In cases of EIPH, many utilize diuretics, such as Lasix, which really has no direct impact on the airways or lungs, but more so acts by reducing blood volume and blood pressure. Medications are warranted in many cases, especially if severe, but we have to keep in mind that there are side effects.  Bronchodilators not only stimulate the airways to open, but they also stimulate the heart to pump, thereby increasing heart rate and blood pressure. In some competition horses, this stimulation has led to abnormal heart rhythms and even cardiac arrest. Diuretics also reduce blood volume, can contribute to mild dehydration and electrolyte disturbances which can lead to various negative effects and in some, actually make problems such as IAD or even stomach ulcers worse, due to drying of tissues with long term use. Steroids, corticosteroids, can have disasterous long term effects in the horse ranging from immune dysfunction to laminitis and even organ damage.
  3. Diet: Diet is a huge contributor to inflammation and we have to remember that almost all of these chronic airway problems stem from inflammation. What we have to do in many is re-evaluate the diet, determining if some components may actually be pro-inflammatory in nature for that horse.  In the end, I have found that by moving to a cleaner and simpler diet, the patients often respond favorably.
  4. Supplements/Herbs:  Many of these patients are on high supplement loads, from vitamin/mineral combinations to products designed to ‘open’ airways.  Some are effective when used properly, while others not so much.  Many actually have medications intermixed, which is something to be cautious of, especially with drug testing.  I think in many cases, the high load of supplements being used in a patient in the hopes that something will work, can actually work against us. I do think, however, that with the right targeted approach, supplements can be very effective and often help us to lower demands or need for pharmaceutical intervention, due to improvement of overall health in that patient.
  5. Surgery:  Surgical intervention is needed for most cases of dorsal displacement or laryngeal hemiplasia, especially if the problem is creating major issues for the patient in regards to airflow. However, this is not always the case, as many of these horses are fine when not competing (retired) and many have improved dramatically with the right herbal supplement approach.

My Personal Approach to a Coughing Horse:

The majority of horses that I consult with are chronic in nature, meaning that the condition has been present for many months if not years.  Almost all of these cases involve asthma (IAD or COPD), which is really an allergic response.  In those cases, most have been on pharmaceutical medications, including bronchodilators, steroids and diuretics as part of their daily or pre-competition regimen, for years. What is interesting when it comes to medication use is that it is often viewed as the first line of therapy for any given condition, which it should if the case warrants it, however, most do not.  These medications are not really ‘fixes’ for the problem at hand, and more often are bandaids in the competition horse.  Due to not resolving the main underlying problem, the horses often require higher and higher doses to achieve the same results, which is due to condition deterioration or progression.  This is evident in the COPD horse that requires higher and higher doses of steroids or the EIPH racehorse that requires higher and higher doses of the diuretics. We should see this increasing dose need as a sign, but many do not until it is too late. So, by the time I am consulting with that owner, more than often, we have long term lung and tissue damage, which is usually permanent and will impact the outcome.  Better to intervene early in my opinion.

In all of these patients, what we are trying to do is target the approach with therapy.  Here, we want to target two processes; inflammation and immune dysfunction, which are interconnected. We have to realize that this inflammatory response present in the lungs is not just in the lungs, but is also present throughout the body. We want to modify this response, return it to a normal, healthy level.  In doing this, we have to seek out culprits which may be instigating the issues, such as diet, environment, stress and even current medication/supplement regimens.

I choose to use herbs in our patients and often get some incredible responses.  Herbs allow us to do several things, of which include providing nutrients to the body, but also taking advantage of medicinal properties of those herbs to target specific cellular processes that are occuring.  There are many herbs that can provide clinical benefits, each with its own properties and indications.

In cases of COPD and overt allergies with mucous production, we will utilize the Cur-OST® EQ Total Support and EQ Immune formulas.  The EQ Total Support allows us to modulate that inflammatory response, but also target underlying gut dysfunction and inflammation, which are often contributing.  The Cur-OST® EQ Immune formula allows us to also modulate the immune response, which is tied in with inflammation, helping to return it to a more healthy and normal level. This combination helps us to also dry up mucous production, which then assists the patient long term with overall breathing and coughing.

In cases of IAD, it can be a little tricky. Given that IAD and COPD are not really far removed from one another, often we will use the above combination of the Cur-OST® EQ Total Support and EQ Immune formula, especially if the patient is an easy keeper type or has prior gut problems.  In others, we will use a combination of the Cur-OST® EQ Plus and EQ Stomach, with or without the Cur-OST EQ Immune formula, especially if there is little to no mucous production.  Here, the EQ Plus allows us to balance that inflammatory response and the EQ Stomach formula actually assists us in moisturizing delicate tissues, which are often dry and irritated in these cases.

I believe, and experience tells me, that if we keep the regimen simple, modify diet and make other needed changes, many of these patients respond quite well and do better than they were previously.  However, there are exceptions to this. Improvement can always be achieved, but the degree to which we experience that improvement will be dictated by the severity and chronicity of the condition.  The longer it has been present and active, the more tissue damage that has been done. Many no longer require medicational intervention, while others can reduce their needs or some still require medication assistance.  Again, this is dependent on the condition and degree to which it is present.

Our goal here is not to ‘cure’ the patient of the condition, but more so our goal is to ‘restore health’ and thereby reduce the incidence of that particular problem.

We are here to help.  I hope this information proves to be of value to you.

Thank you.

Tom Schell, D.V.M.
Nouvelle Research, Inc.

www.nouvelleresearch.com

 

* Horse anatomy image courtesy of Google images

 

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