A healthy respiratory system is essential to every horse's well-being and athletic performance. Like humans, horses rely on their lungs and airways to deliver oxygen throughout the body, but the demands placed on their respiratory system increase dramatically during exercise. Efficient oxygen exchange allows working muscles to perform, while the respiratory tract also serves as an important defence system by filtering and removing dust, bacteria, ammonia, and other airborne irritants. Although mucus, coughing, sneezing, and nasal discharge help clear the airways, excessive amounts of these signs may indicate an underlying respiratory problem.