Diseases of the respiratory tract are common in horses of all ages and types.
Respiration is a cellular activity, and the respiratory tract is the organ that permits
respiration to take place. The requirements placed on the respiratory system
by the body’s metabolism include the transfer of the precise quantity of
oxygen from the inspired air to the arterial blood that the body tissues need,
and the removal from venous blood the quantity of carbon dioxide they produce
by metabolism. These requirements for respiration increase dramatically
during exercise, and the respiratory system of the horse is designed to permit
wide fluctuations in the amount of gas exchange taking place within the lungs.