Respiratory system of the horse
The respiratory system of the horse is the biological system by which a horse circulates air for the purpose of gaseous exchange.
Anatomy
The respiratory system begins with the nares, commonly known as the nostrils, which can expand greatly during intense exercise. The nostrils have an outer ring made of cartilage (the
The nasal passages contain two
In parallel to the main nasal passages, the horse has a complex system of paranasal sinuses - air filled spaces within the head which communicate with the respiratory tract, and serve to reduce the weight of the head. These consist of:
- conchae, forming the concho-frontal sinuses. Drainage into the nasal passages is via the caudal maxillary sinus.
- Maxillary sinuses: within the maxilla, above the tooth roots. Each is divided into two components, the rostral maxillary sinus in front and the caudal maxillary sinus behind. They do not communicate. In addition, each of these is subdivided into a medial (inside) and lateral (outside) component, by an incomplete bone wall that carries the infraorbital canal containing nerves and blood vessels. The close proximity to the tooth roots mean that as the teeth erupt with age, the maxillary sinuses become larger.
- Sphenopalatine sinuses: within the palatine and sphenoid bones, these connect to the caudal maxillary sinus.[1]
A flap of tissue called the soft palate blocks off the pharynx from the mouth (oral cavity) of the horse, except when swallowing. This helps to prevent the horse from inhaling food, but does not allow use of the mouth to breathe when in respiratory distress, a horse can only breathe through its nostrils. For this same reason, horses also cannot pant as a method of thermoregulation.
The genus
The larynx lies between the pharynx and the
At the bifurcation of the trachea, there are two
The lungs are expanded with the help of the
Respiration rate of the horse
An adult horse has an average rate of respiration at rest of 12 to 24 breaths per minute.[3] Young foals have higher resting respiratory rates than adult horses, usually 36 to 40 breaths per minute.[3] Heat and humidity can raise the respiration rate considerably, especially if the horse has a dark coat and is in the sun. The respiration will often change if the horse becomes excited or distressed, and can therefore be useful in determining the health of the animal.
At the gallop, the horse breathes in rhythm with every stride:[4] as the abdominal muscles pull the hind legs forward in the "suspension phase" of the gallop, the organs within the abdominal cavity are pushed backward from the diaphragm, thereby bringing air into the lungs and causing the horse to inhale. As the neck is lowered during the extended phase of the gallop, the hind legs move backward and the gut contents shift forwards, pushing into the diaphragm and forcing air out of the lungs.[5]
Ability to smell
The horse's olfactory receptors are located in the mucosa of the upper nasal cavity. Due to the length of the nasal cavity, there is a large area of these receptors, and the horse has a better ability to smell than a human. Additionally, the horse also has a
Respiratory diseases
- Influenza
- Left Recurrent Laryngeal Hemiplegia("Roaring")
- Recurrent airway obstruction ("Heaves"), akin to COPD or emphysema in humans.
- Strangles (Streptococcus equi infection)
- Rhinopneumonitis
- Exercise induced pulmonary hemorrhage
- Equine nasal cysts
- Ethmoid hematoma
- Nasal polyps
- Bacterial sinusitis (Empyema)
- Bacterial pleuropneumonia
- Dorsal displacement of the soft palate
- Silicosis
External links
References
- ISBN 9783899930030.
- ^ Riegal, Ronald J., and Susan E. Hakola. Illustrated Atlas of Clinical Equine Anatomy and Common Disorders of the Horse Vol. II. Equistar Publication, Limited. Marysville, OH. 2000.
- ^ ISBN 9781118504826.
- ^ "Galloping And Breathing At High Speed" (Press release). American Physiological Society. 2008. Retrieved 6 October 2015.
- ^ Harris, Susan. United States Pony Club Manual of Horsemanship, Vol. III. Wiley Publishing, Inc. Copyright 1996.
- PMID 3492246.