Horses, unlike many other mammals, generally do not breathe through their mouths. They are considered obligate nasal breathers, meaning air intake and expulsion primarily occur through their nostrils. This unique adaptation influences their behavior and health, and understanding it provides insight into their well-being.
Why Horses Primarily Breathe Through Their Nose
The horse’s respiratory anatomy is designed for exclusive nasal breathing. A key structure is the soft palate, which is notably long in horses, extending from the hard palate to the base of the epiglottis. This soft palate divides the pharynx into oral and nasal compartments, ensuring air bypasses the mouth and flows directly from the nasal passages to the lungs.
The epiglottis, a piece of cartilage at the back of the throat, rests snugly on top of the soft palate when the horse is not swallowing. This creates a tight seal that prevents air from entering the trachea via the mouth. This anatomical arrangement means air travels exclusively through the nostrils, into the nasal passages, and then into the lower airways.
This specialized breathing mechanism offers several advantages. Air entering the nostrils is filtered by hairs and mucus, warmed, and humidified as it passes through the nasal passages before reaching the lungs. This protects lung tissues from dust, debris, and extreme temperatures. The constant seal also prevents food or water from being accidentally inhaled into the lungs during swallowing, a crucial protective reflex.
When a Horse Opens Its Mouth
While horses are obligate nasal breathers, they open their mouths for reasons other than respiration. Normal behaviors include eating and chewing, vocalizing through whinnies or neighs, and yawning. Foals may also exhibit “mouthing” as a submissive gesture towards older horses.
An open mouth can also signal discomfort, distress, or a medical issue. Pain, such as from colic, dental problems, or laminitis, may cause a horse to gape its mouth. Poorly fitting bits or tack can also cause mouth opening as a sign of discomfort or to evade pressure during ridden exercise.
In serious situations, an open mouth can indicate a health emergency. Choke, an esophageal obstruction where food becomes lodged, often results in drooling, discomfort, and an open mouth, though it does not typically involve oral breathing. Severe respiratory distress, from conditions like upper airway obstructions or infections, may cause a horse to open its mouth in an exaggerated effort to breathe, even if effective air movement through the mouth is minimal or impossible. True mouth breathing, where air is actively drawn in and out, is an abnormal symptom indicating a severe respiratory compromise and necessitates immediate veterinary intervention.