Horses are classified as obligate nasal breathers, a physiological trait that is rare among mammals, meaning they must breathe exclusively through their nostrils. This unique biological limitation is enforced by a specific anatomical arrangement within the horse’s throat. This specialized structure effectively separates the pathways for air and food, ensuring the respiratory tract is only accessible via the nasal passages. Unlike other animals, the horse’s mouth is reserved solely for eating and drinking.
The Unique Anatomy of the Equine Pharynx
The physical restriction on oral breathing results from the unique structure and relationship between the equine soft palate and the epiglottis. The soft palate is a muscular sheet that extends back from the hard palate, separating the oral cavity from the nasal passages. In horses, this soft palate is unusually long, reaching about six inches in an average animal.
The posterior edge of this extended soft palate fits snugly around the base of the epiglottis, a triangular piece of cartilage that is part of the larynx. This arrangement creates an overlapping seal that divides the pharynx, the shared area for air and food, into distinct respiratory and digestive compartments. The soft palate remains fixed in this position at all times except during swallowing.
The Mechanism of Obligate Nasal Breathing
Breathing is controlled by the constant, intimate contact between the soft palate and the epiglottis, which creates an airtight mechanical lock. The epiglottis rests on top of the soft palate, effectively blocking the entry of air from the mouth into the larynx and trachea. This sealing mechanism ensures that the only pathway for air to enter and exit the lungs is through the nasal passages.
When a horse breathes, air moves from the nostrils, through the nasal cavity where it is filtered and warmed, and then continues over the epiglottis and into the trachea. Only when the horse swallows does this seal temporarily break, allowing the soft palate to elevate and the epiglottis to seal the laryngeal opening, directing food into the esophagus. The soft palate quickly returns to its resting position beneath the epiglottis after swallowing, restoring nasal airflow.
Functional Advantages of Nasal Breathing
This anatomical commitment provides several functional advantages related to the horse’s life as a grazing prey animal. The separation of the respiratory and digestive tracts means horses can graze continuously without risking the inhalation of food particles. This design allows for simultaneous processing of food and oxygen, which is beneficial for an animal that spends a large portion of its day feeding.
During strenuous exercise, this fixed airway allows for maximal, uninterrupted airflow through the nose. When a horse reaches a gallop, its breathing becomes synchronized with its stride, taking one breath per stride. This obligate nasal breathing helps maintain a consistent breathing rhythm mechanically linked to the movement of the body, maximizing oxygen delivery.
Exceptions and Misconceptions
Since horses cannot breathe through their mouths under normal circumstances, an open mouth during exercise or distress is a serious sign of a problem. A common misconception is that “choke” is a respiratory issue, but it actually describes a blockage of the esophagus, which is a digestive tract problem. However, anatomical abnormalities or pathological conditions can force oral airflow, such as in cases of extreme respiratory distress.
One specific condition is dorsal displacement of the soft palate (DDSP), where the soft palate moves upward to sit above the epiglottis, partially obstructing the airway. This displacement causes a characteristic gurgling noise and may lead to the horse breathing through its mouth as a symptom of severe air restriction.
In veterinary medicine, an oral airway might be established via a tracheotomy in an emergency. This procedure bypasses the nasal passages entirely to save the animal’s life.