Respiratory Disease in the Horse

Anyone that has owned a horse has probably experienced respiratory disease in some shape or fashion.  Much the same as humans, horses are prone to developing upper and respiratory infections due to viral and bacterial invasion, but the two most common and troubling conditions affecting horses in today's industry is chronic obstructive pulmonary disease (reactive airway disease) and exercise induced pulmonary hemorrhage (EIPH).  Being a veterinarian working on horses for over 18 years, I have certainly encountered my fair share of COPD patients as well as EIPH athletes.

The respiratory tract plays a vital role in health, performance as well as day to day activity.  In the horse, air is taken in through the nasal passages, down the trachea and into the lungs were carbon dioxide is exchanged for oxygen to fuel cells.  Any problems encountered during this course of airflow can impact oxygen flow to the body and overall performance.  Now, you have to understand that despite the ongoing research with these two conditions, we still not know the exact causes and how to best manage COPD or EIPH.  What I can say is my personal opinion as a veterinarian as to what I feel is the cause or contributing factors, which are substantiated by research.  I feel it is vital that we take a different approach to these conditions, using a combination of therapies to best provide relief.

COPD is an allergic type airway condition in which the horse develops difficulty breathing, usually at set times of the years when allergens are high.  The condition can result in coughing, flared nostrils indicating labored respirations as well as decreased performance.  In mild cases, the condition can come and go in relation to various allergen levels but in chronic cases, the condition can become persistent with little change in respiratory patterns throughout the year.  In many cases, once the condition is diagnosed, therapies include inhaled medications to dilate airways, injectable or oral steroid medications to control inflammation as well as antibiotics to tackle secondary infections.  In addition, usually there are changes made to the environment to help reduce allergen load.  COPD has been shown to have a dramatic inflammatory component which results in the over response of the immune system to allergens, as well as airway constriction and mucous production which plugs up the airways.  The bottom line in my eyes is the inflammatory reaction that is taking place and whether or not we can address this more effectively.

EIPH is a condition in which there is bleeding within the lung tissue, generally associated with higher levels of exertion seen in racing Thoroughbreds and Quarter Horses, but can affect any horse during competition.  The bleeding in the airways produces coughing, affects performance and usually results in evident blood in one or both of the nares.  The exact cause of the condition is not known but it is theorized that multiple factors play into the problem including changes in airway pressures, high pulmonary blood pressures, upper airway obstruction and small airway disease.  Current therapies are essentially targeted at reducing the amount of bleeding and thus improving performance.  The most common medication used is a diuretic called Lasix or Salix.  Again, just as in COPD, there is plenty of research out there discussing how inflammation is associated with EIPH, which not only can impact air flow due to airflow constriction, but also impact healing of airways with scar tissue formation.  Considering the overall impact of inflammation on the body and cellular function, I question what the impact is on the overall health of the cells composing the pulmonary vessels, which may lead to a weakened state and a vessel that is likely to fail under certain conditions resulting in bleeding.  It is just a theory in my mind, but seems plausible but needs to be explored.

In my practice, I have conducted several field trials evaluating inflammation and oxidative stress in a variety of conditions affecting horses.  What I have found is that in both COPD and EIPH, there is a definite inflammatory component which is also accompanied by oxidative stress.  Now, one has to remember that the basics of oxidative stress is that there is an abundance of free radicals generated which can result in cellular damage.  In most cases, the free radicals are neutralized per se by the presence of antioxidants.  What I feel is occurring is that either these horses are not consuming enough antioxidants or the right combination of antioxidants or they are experiencing an overwhelming level of free radicals that is quickly depleting the stores.  I believe that one of the most important aspects of these conditions to address is the inflammation, which I don't feel is being addressed adequately with today's therapies.  Race horses are under a tremendous amount of physical and mental strain, which can contribute to inflammation levels.  Those horses afflicted by COPD are generally systemically inflammed in my opinion, in which we are just seeing the evidence manifested in the respiratory disease.  Today's therapies are helping to control a small percentage of these patients and given this, we must ask what more can be done especially considering the potential side effects of the medications being used.  In the race horse industry, medication debates are constantly being raised.  We need to seek out other viable options not only in terms of therapies, but to also potentially use as preventative to improve the health of these animals.  What we are seeing clinically is a direct manifestation of what is occurring deep within and a sign of imbalance to one degree or another.

Just my thoughts.

Tom Schell, D.V.M.