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Is Small Airway Disease Of Significance In The Healthy Equine Athlete?

Updated: May 8, 2023

The answer is, unfortunately, a resounding "YES". Minor degrees of airway inflammation and small increases in mucus production quickly take their toll on the equine athlete attempting to take 150 breaths per minute, as is the case of the average thoroughbred galloping. For example, a two to three percent loss of performance will take a horse from first place to a distant last.

Another complicating factor is that horses do not have a sensitive cough reflex. There can be quite a lot of mucus in the horse's airways without it coughing. This is a sharp contrast to humans and dogs. An endoscopic examination of the airways can reveal large amounts of mucus in a horse with no history of coughing. Remember, a horse with respiratory disease does not necessarily cough.

This covert or subclinical small airway disease in performance horses has been named Lower Respiratory Tract Inflammation (LRTI). While it is not a full-blown allergy as in heaves, it is an inflammatory response.

If a sample of mucous material is collected from the lungs, large numbers of neutrophils (pus cells) are usually found. Significant bacterial infections are often also found when the samples are taken to the microbiology laboratory. The significance and number of such bacterial infections were highlighted in a large track study just recently. These bacteria can be the primary cause of the problem, or they can be a secondary complicating issue following a viral infection.

There are believed to be three common causes of small airway disease:

  1. Infectious agents-including bacteria and viruses

  2. Airborne dust-mold spores are the most common constituents and cause for concern in the air of stables. When inhales in large enough numbers, these spores can cause inflammation and irritation of the small airways in horses that do not suffer allergy.

  3. Noxious gases-the most common noxious gas to which horses are exposed is ammonia

It should always be highlighted that the above causes can interact in many ways. For example, dust can increase a horse's susceptibility to an infection. Equally, a horse suffering a respiratory tract infection in a dusty environment will take a lot longer to recover than if it was breathing fresher air.

Another example of the ways the above factors can interact has been demonstrated using nuclear medicine studies. These studies showed that it takes a month for the cilia lining the airways to recover their function following a bout of influenza. So, while the horse looks sick for only a few days, its lungs will take up to a month to recover. This was all based on average tracheal clearance rates over 40 days. At this time, the lungs will also be very sensitive to the inhalation of airborne pollutants.

***t can take a month for the lungs to recover from a viral infection***

With the motto of "prevention being the best cure", emphasis should be placed on providing fresh air. Both the provision of fresh air and therapeutic agents are particularly beneficial to getting horses back to full health and fitness to meet their true athletic potential.


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