The equine (and human) respiratory system is composed of: mouth, nasal cavity, nasal cavity, frontal sinus, pharynx, larynx, trachea, lungs, bronchioles, bronchioles, diaphragm, ribs and intercostal muscles. Since horses breathe only through their nose, the nostrils are the main entrance/exit to and from the airways. The primary function of the horse's respiratory system, especially during training, is to ensure gas exchange: it supplies oxygen to the blood, removes carbon dioxide from the body, and participates in thermoregulation and maintenance of the acid-base balance.

Respiratory rate

It is important to know your horse's normal vital signs (or TPR: temperature, pulse and respiratory rate), which will give valuable indications about its health. You can measure breathing rate by feeling the air coming in and out of your horse's nostrils, or by observeing/feeling the movement of your horse's chest or flanks over a minute. Listening to the breathing with a stethoscope placed on the trachea is even better. One beat corresponds to one breathing cycle: one inhalation + one exhalation. The average normal breathing rate for an adult horse is between 10 and 20 cycles per minute. For a newborn foal it will be higher; about 20 to 40.

Of course, these are general figures that will vary depending on the horse and the situation. The environment, as well as stress or excitement, can have an impact on the respiratory rate. If the horse is particularly relaxed, you can even achieve a frequency as low as 4 cycles per minute. Checking these signs regularly will help you to set normal values for your horse.

In addition to frequency, it may be useful to pay attention to breathing characteristics which are also good indicators; does your horse make unusual sounds when breathing, is the breath deep or gasping? Strange noises may indicate allergies, pulmonary emphysema, or mucus obstruction in the trachea for example.

Training consequences and recovery

Like heart rate, respiratory rate increases with training, almost linearly with intensity. It can rise to 180 cycles per minute during very intense exercise. The respiratory system responds to training stimulation by dilating the horse's airways, reducing resistance and increasing airflow. The muscles of the upper airways will allow more oxygen to enter the horse's system, and help to eliminate carbon dioxide, the production of which will also increase with effort. Respiratory rate and frequency of lung contraction will also increase, respectively managing carbon dioxide accumulation and allowing more air transfers.

Breathing rate recovery time can also be used as a fitness indicator, although it is not recommended to use it alone as it is highly variable. The frequency as well as the sound of the breathing are useful to evaluate it. Depending on training, the normal recovery time (i.e. the time it takes for the breathing rate to return to normal values) is 15 to 20 minutes. The horse's rapid and heavy breathing will decrease and the dilated nostrils will return to normal.

The faster your horse's breathing will drop after the effort, the fitter he will be. This is particularly important to note for sports horses preparing for the competition season. For example, a thoroughbred horse that returns to a normal breathing rhythm 3-4 minutes after completing a cross-country course will not need any further preparation. [By the way, if you want to learn more about the physical preparation of the horse for the competition season, read our article written with two-time European Young Riders Champion Marie-Charlotte Fuss.]

A horse panting, with a short, rapid breath after the effort may have been over-trained and/or may be overheated. If the recovery period is long and the horse is still breathing with difficulty after 5 minutes of walking in a quiet place for example, it is best not to ask for too much effort for a few days. Finally, any abnormal noise or runny nose may indicate a problem that needs to be addressed.

The limits of the respiratory system

Several factors limit the efficiency of the respiratory system such as lung volume, airway diameter, and the horse's gait. Indeed, contrary to walking and trotting, where the respiratory frequency will adapt to the oxygen demand of the horse's organs, at gallop it will be exactly coupled to the frequency of the strides. Thus, the only way to increase the respiratory rate to better meet the oxygen demand will be to increase the gait, which will tire the horse and further increase the oxygen demand. During long and intense efforts, the horse will therefore necessarily lack oxygen and present hypoxemia (1) and hypercapnia (2).

As far as lung volume is concerned, although horses have a lung capacity of 50L of air, 60% of the air breathed does not participate in gas exchange, making this large capacity rather useless. In addition, horses breathe through their nostrils, one of the narrowest parts of the respiratory system along with the larynx. This causes resistance, which will limit the air breathed in during effort, despite the dilation of the nostrils and larynx.

Training will have no real effect on the respiratory system compared to the muscular or cardiovascular systems. Indeed, it is the adaptation of the latter two systems that will, for example, lead to an increase in oxygen absorption and a decrease in respiratory fatigue. It will not be possible to increase the ventilation capacity of the lungs or the speed of gas exchange (oxygen and carbon dioxide); factors that determine exercise capacity.

The only improvement that can occur with training is the strengthening of the muscles of the upper airways (nasal, pharynx, larynx), but there will be no real change in the respiratory system. Indeed, research has shown that training has little effect on the lower respiratory tract, and concluded that the horse's respiratory system is not well adapted to the demands of the sport horse.

Some tips for good respiratory health

Other factors will affect air intake and gas exchange during the effort, thus limiting the horse's maximum performance, such as air quality (pollution, humidity...), the position of the horse's head and neck, and the equipment used. These factors are easier for riders to take into account, who can then try to limit the impact on their horse's breathing.

There are several methods of stable management that can prevent and limit risk factors for equine respiratory health, which are numerous and include general horse health as well as environmental and even nutritional factors.

-> It is important to maintain good air quality in the stable with a good ventilation system, and to give the horses as much time as possible outside
-> To reduce dust and pollution, it is advisable to use wheelbarrows, limit the use of machinery in the stables and riding arenas, and minimize any human activity (sweeping, harrowing, etc.) especially when horses are present
-> To keep training areas free of dust, it is often necessary to water
-> Quality, dust-free bedding is preferred to ensure the health of the horses' respiratory system
-> Wetting the hay and not feeding the horses on the ground will also reduce their dust inhalation
-> Finally, to prevent diseases, disinfecting the water and pellet buckets is a good habit to have, as well as having a complete vaccination program adapted to each horse

See you soon for a new article,

The Seaver Team