Prevalence of upper respiratory tract disorders detected with a flexible videoendoscope in thoroughbred racehorses.

A total of 350 thoroughbred racehorses found clinically as having coughs or abnormal breath sounds underwent endoscopic examination of the upper respiratory tract at rest. As a result, abnormal endoscopic findings were obtained in all horses, demonstrating that thoroughbred racehorses with a clinical abnormality in the respiratory system necessarily had disorders in the upper respiratory tract. Whereas 11 types of disorder were observed, a combination of three different types of disorder were found in the highest frequencies in 3-, 4- and 5-year-old horses (27.8%, 29.2% and 29.7%, respectively). Among 6-year-olds or older horses, those having only one type of disorder accounted for the greatest proportion (47.6%). The prevalence of pharyngeal lymphoid hyperplasia or abnormalities of the epiglottis decreased with age.