Upper and Lower Respiratory Issues in the Equine

Oct 6, 2011
Chris Thomas

Roaring Horses Affected by Inspiration - Trish Steel; Geograph.org

The way a horse breathes and the way that the respiratory system is put together predisposes different ailments during inspiration and expiration.

The dynamics of the horse’s respiratory system help to explain why some obstructions of the airways are more inclined to happen whilst the horse is breathing in, while others occur more commonly when the horse is breathing out.

The horse’s respiratory system is made up of:

the nostrils and nasal cavities
larynx
trachea
bronchus and bronchioles
alveoli (air sacs)
lungs and pleura

At a point when the horse is exercising at its maximum capacity, it isn’t uncommon for dynamic partial collapse to occur. That is, the airways are provided with resistance in the form of the nostrils collapsing inwards, reducing the amount of air that can be taken in. This has a bearing on different parts of the horse’s respiratory system, depending on whether the horse is inhaling or exhaling.

The horses’ respiratory system can be broken up into the upper and lower respiratory system. Upon inspiration or the act of breathing in, the airways outside of the chest account for more than 90% of the horse’s total pulmonary resistance. That is, the nostrils, nasal cavities and larynx have an affect on how much air can come into the lungs.

Upon expiration, the intrathoracic airways – or those within the chest – are responsible for more than 50% of the horse’s total pulmonary resistance. That is, the lungs, alveoli and bronchus have a greater role affecting the expiration of air. This division of roles based on inspiration and expiration, can help to explain why certain respiratory problems occur during inspiration, whilst others are prevalent upon expiration.

The Roaring Horse

Left laryngeal hemiplegia, more commonly known as ‘roaring’ or ‘whistling’, is a disorder of the larynx. Because the upper respiratory tract provides the greatest proportion of total pulmonary resistance whilst breathing in, the roaring horse will be affected by the act of inspiration, more so than expiration.

On the other hand, recurrent airway obstruction (RAO), is a lower airway disorder. Because of this, issues arising from this problem are more commonly apparent when the horse is exhaling. This is due to the fact that total pulmonary resistance is greatest in the lower airways when the horse is breathing out.

The horse’s lungs are one thing that cannot be improved by training. Consequently, it is important for all who are utilising equines as athletes to look after their horse’s respiratory system. An awareness of what makes up the respiratory system and problems that can occur will aid the horse owner in finding ways to prevent such problems from arising.