10 Things You Might Not Know About the Horse’s Respiratory System
The horse does not breathe through its mouth and nose like we do. The horse only breathes through its nostrils. The nasal passages in the horse are separated from the oral (mouth) cavity. They do not breathe through their mouths unless they have some injury or abnormality to the soft palate (the structure that separates the mouth from the nasal passages).
At canter and gallop normal horses take one breath perfectly in time with one stride. This is referred to as respiratory-locomotory coupling. A normal horse may swallow 1-2 times during each minute of exercise, but no more. The amount of time taken to inhale is the same as the time taken to exhale.
The amount of air moved in and out of the lungs increases in direct proportion to how fast the horses is running. If a horse runs twice as fast it must move twice as much air in and out.
During exercise, when horses inhale, around 90% of the resistance (obstruction) to air movement is in the airways that are in the head, namely, the nostrils, the nasal passages and the larynx. But when horses are exhaling the majority of resistance to air movement (55%) is in the airways within the lung.
If you tighten a horse’s girth too much, then it will affect it performance not because of constricting the chest and preventing the lungs from expanding but because it decreases the effectiveness of the muscles around the front of the chest and shoulder that move the forelegs.
Horses do not breathe by expanding and contracting their chest during canter and gallop. They expand and contract the chest when breathing at rest, when breathing at walk and trot, and perhaps most noticeably when blowing hard after exercise. But during canter and gallop, the air moves in and out along the lines of a syringe with the stiff wall of the syringe representing the chest and the plunger the diaphragm i.e. all air movement during canter gallop comes from movement of the diaphragm.
Horses hold their breath over jumps and do not breathe again until they land, starting with breathing out.
You cannot train the respiratory system of the horse. Plenty of books will tell you that you can. A number of scientific studies show the reverse. The amount of air moved in and out by an unfit horse at a fixed speed will be the same 6 months later when that horse is fully fit.
The blood pressure in the blood vessels within the horse’s lung (referred to as pulmonary blood vessels) during galloping increases around 4-5 times above that at rest.
This is one of the factors that puts stress on the very thin walls of the blood vessels and leads to some of them rupturing.