Cryptorchidism in Horses

Cryptorchidism is a congenital condition (i.e., the individual is born with it) in which one (unilateral) or both (bilateral) of the testes fail to descend into the scrotum. A number of common terms have been used to describe cryptorchids,

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Cryptorchidism is a congenital condition (i.e., the individual is born with it) in which one (unilateral) or both (bilateral) of the testes fail to descend into the scrotum. A number of common terms have been used to describe cryptorchids, including "rig," "false rig," and "ridgling." Embryologically, the testes develop high in the abdomen near the kidneys. During fetal development they migrate down through the abdomen, passing through the inguinal rings, and eventually reside in the scrotum, usually by the 9th to 11th month of gestation.

When the testis and epididymis (the duct that stores sperm as it matures) are retained within the abdomen, the term abdominal cryptorchid is used. When the tail of the epididymis and/or variable amounts of the deferent duct (runs from the epididymis to the urethra) extend into the inguinal canal (allows passage of the spermatic cord), it’s termed an abdominal or abdomino-inguinal cryptorchid. When the testis is in the inguinal canal, the term inguinal cryptorchid or the more vernacular "high flanker" is used.

The testes are maintained in the scrotum at a lower temperature than the rest of the body’s organs. This is important because in order for normal spermatogenesis to occur, the testes must be 4-6°C (5-9°F) below core body temperature. Therefore, cryptorchid testes cannot produce sperm normally, and a bilateral abdominal cryptorchid would be sterile.

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Written by:

Steven P. Brinsko, DVM, MS, PhD, Dipl. ACT, an Associate Professor and Chief of Theriogenology at Texas A&M University, received his DVM from the University of Florida, MS from Texas A&M University, and PhD from Cornell University; he is also a board certified specialist in the American College of Theriogenologists (Veterinary Reproduction). His interests include all areas of equine reproduction with emphasis on the stallion. Dr. Brinsko has given numerous presentations at national and international meetings and has authored or co-authored over 100 scientific publications as well as 11 book chapters related to the field of reproduction.

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