The sound to which this term is applied is produced in the act of breathing while the air is being expelled from the lungs during forced respiration. It is most marked while the horse is doing a brisk canter, and becomes less audible in the gallop. It is always most pronounced at starting, and is recognized as a fluttering or loud vibrating noise. The degree of vibration differs in different animals, and it is distinctly more sonorous in some than in others.
High blowing is essentially a nasal sound, and although sometimes loud and shrill, it bears no comparison in point of quality with the noise emitted as the result of laryngeal disease in roarers and whistlers.
It is more especially observed in horses with thin skins, whose false nostrils are loose and capacious, and in animals of .xcitable temperament. In the writer's experience high blowers are conspicuous for the soundness of their breathing organs and endurance under exertion, and in a large practice in the examination of horses of every description he does not remember to have found roaring to be associated with this peculiar breathing sound. Increased nasal resonance or noisy breathing is sometimes the result of that type of conformation in which the face presents a narrow and pinched appearance across the region of the nose. In this condition the sound has the quality of that ordinarily heard in respiration, but much intensified.
It is readily distinguishable from roaring, and is not to be regarded as a state of unsoundness.