NOVEMBER 2005 • VOLUME 3 • HORSES For LIFE™ Magazine

Research shows that Horses are having problems Breathing!!

10 year old research! Why haven't you heard about it?

Are you doing something that might interfering with your horse's breathing!

Who is more at risk?? You might be surprised to find out. The dressage horse, the race horse, the jumper, the reining horse? But you can prevent this by learning about proper collection and head frame.

Be informed!

Overview of the Equine Respiratory System ( 13-Mar-2002 )

I think most of us would be surprised to find out that the horse is "an obligate nasal breather and all the air needed for gas exchange, at rest and during exercise, must pass through the upper airway" (Derksen et al.). A few studies have demonstrated that the "upper airway provides a high resistance to airflow and may be a limiting factor in the horse’s exercise capacity". For this reason researchers believe that those interested in the athletic horse should have a thorough understanding of upper airway function.

In the horse, as in most mammals, upper airway resistance is a significant portion of total resistance to flow, due in part to the fact that the air must make its way through the infoldings of the nasal passages and turn at an angle into the nasopharynx which then connects with the tracheal opening. In the horse, a full two-thirds of the total resistance to airflow resides in the upper airway. This proportion increases during exercise.

Because of this, during exercise most animal species switch to mouth breathing. This provides a low-resistance pathway for the greater airflow required during exercise, thereby minimizing the work of breathing. Surprisingly, the horse cannot breathe through its mouth efficiently and the more than 20-fold increase in airflow that occurs during exercise must be totally accommodated by the upper airway. Obligate nasal breathing is the result of a tight seal between the soft palate and the laryngeal cartilages. “ Derksen et al

In resting horses, the air entering the upper airway must turn approximately 90º to flow from the nasal passage into the trachea. That change in direction of airflow contributes to the work of breathing [Petsche et al]. During exercise, the effort needed to change airflow direction is reduced by straightening of the upper airway[Petsche et al]. . Straightening not only allows air a more direct route to and from the lung, it also tends to stretch and stiffen upper airway tissues, making them more rigid and more resistant to collapse.” Derksen et al Essentially this is equivalent to lifting your chin as opposed to lowering it to your chest when you are running.

Jacintha van Beemen

Compounding this problem of obligate nasal breathing...(editors note re infraorbital nerve and pressure by the cavesson) and the change in direction of airflow - a study was done in 1995 looking at this just a little further.

In 1995 Petche et al.  conducted a study on the effects of head position on upper airway function in exercising horses. The study was done using Standardbred trotters and while they were exercising with their neck unrestrained, extended or flexed, the air flow was monitored through the upper respiratory tract.

"The desired head position was achieved by tightening an overcheck (extended head position) or side reins (flexed head position).
[Editors Note: The flexed position had the head on the vertical NOT overbent.]

Petche et al.  found that extension of the head and neck did not affect the upper airway of exercising trotters (1995).

Simplistically, inspiratory impedance is the amount of obstruction there is to the airflow. In this instance animals in the flexed head position had greater difficulty breathing in but not breathing out (Petsche et al., 1995)

This study demonstrates for the first time that head and neck position affects upper airway mechanics in exercising horses.

Upper airway obstruction can be classified as fixed or dynamic. A fixed upper airway obstruction affects airflow on inhalation and exhalation, while a dynamic obstruction primarily affects airflow during inhalation (Gibson et al. 1973).

Furthermore, Art and Lekeux (1991) have shown that longitudinal stretching decreases the collapsibility of tracheal segments in vitro. This implies that tracheal segments may be more susceptible to collapse if they are compressed. This may occur when the horses head is flexed.

Petche et al. postulated that respiratory impedance increased in flexed horses due the bulging of other tissues into the upper airway (1995).

This research originally arose from the thought that airway impedance would be increased if the neck was flexed with the nose tucked into the horse’s chest and decreased if the head and neck was extended (Cook, 1981).

Whatever the reason the research done 10 years ago clearly showed that consistently that flexion of the neck resulted in decreased capacity to breathe.

While this research leaves lots to still question, it was specific enough within the parameters of the research to consider the conclusion quite valid. That is, flexion on the neck can bring about a marked decrease in the ability of the  horse to breathe.

The question then becomes whether this is always true of flexion of the head or are there circumstances in which the upper airway is not partially obstructed. Clearly this may be a warning that overbending for certain and likely other concepts of proper flexion may interfere with breathing. Further research, as always, is required but I hope its something you as a responsible rider will take notice of.

Article by Brie Hamblin

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