10 Equine Respiratory System Facts

1. Horses are obligate nasal breathers, which means a horse only breathes through his nose during exercise.

  • During exercise, it becomes twice as difficult for horses to move air into the lungs due to increased resistance.
  • 50% of the total resistance in the upper airway originating in the nasal passages.
  • When horses inhale during exercise, about 90% of the resistance to air movement is in the upper airways.
  • Try this: place your fingers on your own nose, close your mouth and take a deep breath in. Feel what happens to the soft tissues on your nose... did you feel how they sucked inward? The same thing happens to our horses when they are exercising.

2. The lungs are a rate limiting organ.

  • A horse's lungs have a total capacity of about 60 liters.
  • Due to the chest cavity and size of the heart, they can only use about 18 liters of their 60-liter total capacity.

3. You cannot train the respiratory system of the horse.

  • Unlike bones, heart and skeletal muscle, the lungs don't train with exercise.
  • The amount of air moved in and out by an unfit horse at a fixed speed will be the same as when that horse is fully fit.

4. The amount of air moved in and out of the lungs increases in direct proportion to how fast the horse is running.

  • If a horse runs twice as fast, it must move twice as much air in and out.

5. During canter and gallop, horses do not breathe by expanding and contracting their chest.

  • They expand and contract the chest when breathing at rest, when walking and trotting, and when blowing hard after exercise.
  • During a fast canter and gallop, all air movement comes from movement of the legs and diaphragm. 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.

6. One Breath = One Stride.

  • Horses’ breathing and stride are linked at a canter and gallop - horses take one breath with each stride. This is called respiratory-locomotor coupling.
  • Because of this link, anything that affects the horse’s breathing also impacts his stride.

7. Tightening a horse’s girth too much will affect his performance.

  • This is 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.
  • More strides result in more breaths.

8. Horses hold their breath over jumps.

  • They do not breathe again until they land; then, they begin by exhaling or breathing out.

9. When galloping, the blood pressure in the blood vessels within the horse’s lungs (referred to as pulmonary blood vessels) is 4-5 times greater than when at rest.

10. Increased pressure on the horse's breathing puts stress on the very thin walls of the blood vessels and can cause them to rupture.

  • This bleeding, also referred to as exercise induced pulmonary hemorrhage (EIPH), occurs deep within the lung tissues.
  • Horses that bleed rarely show blood at the nostrils.

Bonus: If opened and laid flat, the airways in the lungs would cover 10 tennis courts!