Testicular Disorders in Equids: A Case Series

Equine testicular disorders represent a diverse group of conditions that impact the longevity of a stallion's breeding career. Stud farm veterinarians should be familiar with the variety of clinical presentations and diagnostic options for these conditions. This retrospective case series reports 57 cases of testicular abnormalities in stallions and donkeys presented to the clinic for further diagnostics and treatment. These disorders included neoplasia (three unilateral and one bilateral seminoma; two Sertoli cell tumors; two Leydig cell tumors; and one malignant mixed sex cord-stromal tumor), six cases of testicular hypoplasia and disorders of sexual development (DSDs), twenty-four cases of cryptorchidism with compensatory hypertrophy/hyperplasia, and two cases of monorchidism. Among the monorchid horses, one of these involved an abdominal retained testicle with a concurrent Leydig cell tumor, whereas the second presented a normally scrotal testis. Additional diagnoses consisted of testicular degeneration, including suspected anabolic steroid-induced hypogonadism, spermatic cord torsion, hydroceles, periorchitis, scrotal sarcoid associated with severe testicular degeneration, parasitic orchitis and periorchitis associated with Strongylus vulgaris and Setaria equina, one infectious epididymitis with orchitis in a donkey, and one case of ectopic adrenal cortical tissue within the testicular parenchyma. Rarely observed disorders included cystic ectasia of the rete testis in a cryptorchid testis and ischemic necrosis following failed laparoscopic castration without orchidectomy. This case series reviews the pathophysiology, clinical presentation, diagnostic techniques, and outcomes of various testicular diseases, providing a guide to facilitate case management in private practice. Additionally, it offers histopathologic descriptions of most cases, which are often missing from routine diagnostics but are crucial for definitive diagnosis. These findings demonstrate that horse testicular diseases encompass a wide range of neoplastic, developmental, degenerative, infectious, and parasitic conditions that can coexist and often go unnoticed until they progress.