Analysis of risk factors for recurrent airway obstruction in North American horses:: 1,444 cases (1990-1999)

Objective-To identify risk factors for recurrent airway obstruction (RAO) among horses examined at veterinary teaching hospitals in North America. Design-Retrospective case-control study. Animals-1,444 horses with RAO and 1,444 control horses examined for other reasons. Procedure-The Veterinary Medical Database was searched for records of horses in which RAO was diagnosed. A control group was identified by randomly selecting a horse with a diagnosis other than RAO that matched the institution and year of admission for each of the horses with RAO. Information obtained included hospital, admission year and month, age, sex, breed, and discharge status. The association between risk factors and diagnosis of RAO was estimated with logistic regression models. Results-The risk of RAO increased significantly with age, with horses greater than or equal to 7 years old being 6 to 7 times as likely to have RAO as were horses less than or equal to 4 years old. Thoroughbreds were 3 times as likely to have RAO as were ponies. Horses were 1.6 and 1.5 times as likely to be examined because of RAO during winter and spring, respectively, than they were during summer. Conclusions and Clinical Relevance-Results suggest that RAO was more likely to be diagnosed in females, horses greater than or equal to 4 years old, and Thoroughbreds and that RAO has a seasonal distribution.