Retrospective Evaluation of Cryptorchid Sidedness at Colorado State University Between 1984 and 2014 and Oakridge Equine Hospital Between 2008 and 2023.

Cryptorchidism is a common congenital disorder in male horses characterized by the failure of one or both testes to descend into the scrotum. This developmental anomaly has important clinical, surgical, and economic implications, particularly in breeding animals. This retrospective study investigates the prevalence and laterality of cryptorchidism in a large equine population presented to two veterinary referral hospitals-Colorado State University Veterinary Teaching Hospital (CSU VTH, 1984-2014) and Oakridge Equine Hospital (OEH, 2008-2023). Medical records were reviewed to identify affected horses, and data on breed, age, and laterality of retained testes were collected. Anatomical location of retention (inguinal vs. abdominal) was excluded due to inconsistent documentation across the study period. A total of 777 horses met the inclusion criteria, with Quarter Horses comprising the majority of clinical cases. Quarter Horses exhibited a strong predisposition for left-sided testicular retention, whereas Thoroughbreds and Arabians more commonly presented with right-sided retention. These breed-specific trends in laterality suggest possible developmental factors influencing testicular descent. Understanding these patterns can aid in clinical diagnosis, improve surgical planning, and contribute to evidence-based breeding recommendations aimed at reducing the incidence of cryptorchidism in equine populations.