Morgan Murphy

Understanding Your Horse’s Upper Respiratory Tract.

Respiratory problems are very common in horses. Not only do infections and allergies create problems for leisure horses but they can wreak havoc with working, show and performance horses. As an owner or rider, we recommend having a good understanding of the structure and function of the horse's upper respiratory tract.

The upper respiratory tract of the horse – Courtesy of Merck

 

The Anatomy of the Horse's Upper Respiratory Tract

The horse's upper respiratory tract starts at the nostrils, extends through the larynx, (a cartilaginous structure) and then joins the trachea, which sits atop the horse's lungs. It can be thought of as a hollow, muscular tube beginning at the nose, proceeding down the back of the throat to where the trachea is located.

The nasal passage consists of a paired of nasal cavities which have sinuses to the sides (air filled cavities). The nostrils are separated by a piece of cartilage called the nasal septum. This continues through the upper surface to form the hard palate, a part of the cavity which separates the nose and mouth. As we move into the front of the horse’s mouth, the hard palate turns to soft palate extending through to the epiglottis. This long structure allows the horse to be able to breath exclusively through its nose. This is because the epiglottis sits on top of the soft palate, which effectively prevents air from flowing through the mouth into the lungs.

The larynx is made up of the cricoid, thyroid, and paired arytenoid cartilages, the aryepiglottic folds, the vocal cords, and the glottic cleft (the entrance to the larynx).

The upper airway also involves a great number of muscles, nerves, blood vessels, salivary glands, connective membranes and tissues that help support the function and structural integrity of the respiratory tract.

Function of the Horse's Upper Airway

The main functions of the upper respiratory tract are breathing, swallowing, and vocalization. In horses, breathing issues can be caused by a number of issues.

Air enters the upper respiratory tract through the nose, passes through the nasal cavity where it is filtered and adjusts to body temperature. It then carries on into the nasopharynx, over the epiglottis, and through the larynx into the trachea. The muscles of the respiratory tract help keep the airway open, clear and moving. The horse's tongue also helps breathing by keeping the larynx in the right position. Horses are the only domestic animal who cannot breath through their mouth.

Due to the complex anatomy of the upper respiratory tract, it is no surprise that it is somewhat vulnerable to problems. Included among them are:

  • Dorsal displacement of the soft palate (DDSP) - when the free end of the soft palate is located above the epiglottis instead of under which blocks airflow
  • Nasopharyngeal collapse: The damage of the structure within the nasopharynx causing breathing problems.
  • Laryngeal hemiplegia (roaring): This is where the nerves in the larynx malfunction, which can cause a decrease in airflow to the lungs and in some cases, cause exercise intolerance.

 

Breathing problems can be difficult to manage. Some can be treated, others may require adjusting the horse's workload or lifestyle to accommodate its respiratory dysfunction.

For more detailed articles on equine anatomy and physiology, veterinary care of horses and much more, come back to Morgan’s blog again soon.

 

Permission details for image http://www.merckmanuals.com/permissions.html