The respiratory system of zebras contains two lungs with several small structures that look like bunches of grapes, called alveoli. These diminutive sacs are the final destination of the inhaled air, after passing through the airways: nostrils, pharynx, larynx and trachea, which divides in two shorter and narrower tubes called bronchi. The bronchi enter the lungs, where they branch into several bronchioles, which gradually reduce their size until reaching the alveoli. In the alveoli, the oxygen contained in the air passes to the blood stream by diffusion, while carbon dioxide diluted in the blood enters the alveoli, being later eliminated through the airways.
Inhalations and exhalation are the two respiratory movements. Their main function is to circulate air in and out of the lungs, thus allowing the gas exchange between oxygen and carbon dioxide to happen. During inhalation, the lungs of the zebra are expanded with the help of a muscle called diaphragm, also present in other mammals. The exhalation occurs when the air is expelled from the lungs, which return to their normal size. When resting, zebras can breath in a rate of eight to 14 inhalations per minute.
As are other members of the genus Equus, zebras are obligate nasal breathers. This means that unlike many other mammals, zebras cannot inhale air through their mouths, always needing to take in air through their nostrils. Another adaptation is the guttural pouch, two air chambers located in each side of the neck, which are connect to the trachea and help to regulate the blood temperature when the animals are running.
Zebras can suffer from several respiratory diseases, including the African horse sickness, which is highly contagious and transmitted through midges Culcoides and the bite of other insects; equine nasal cysts, which are a bacterial infection of the sinuses; strangles or equine distemper, a Streptococcus infection of the airways; and obstruction of the nostrils, through maggots and other larval parasites.