Cryptorchidism

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Video: Equine Cryptorchidectomy

Equine Cryptorchidism

Cryptorchidism is a well-known and common disorder in horses. It has been documented in all breeds, although quarter horse breeds appear to be at greatest risk. A cryptorchid horse, also called a rig or ridgling, is a horse with failure of one or both testicles to descend in the fetus from a position behind the kidneys, along the wall of the abdomen, and into the scrotum. The testicle usually reaches the scrotum before birth. However, the testicle can stop at any point along its descent from the abdomen to the scrotum so that it could be “retained” within the abdomen or in the inguinal canal, the passageway between the abdomen and the scrotum. The retained testicle is not as large as the descended, normal testicle, but is still a problem.

The Surgical Process

A testicle must reach the scrotum to become fertile because the retained testicle is subjected to intra-abdominal temperatures that are too high to produce spermatozoa. However, the retained testicle can still produce the hormone testosterone, so the horse behaves like a stallion. In horses, cryptorchidectomy, the term for removal of a retained testicle, is performed so that the horse loses its potentially dangerous and unpleasant stallion-like characteristics. In dogs, the urgency for performing a cryptorchidectomy is driven by the risk of the retained testicle becoming cancerous. This risk has not been demonstrated in horses. Many unilateral cryptorchid stallions are used successfully for breeding, although the theoretical risk of transferring the trait to offspring is a concern.

Current methods for management of cryptorchid horses require laparoscopic removal of the retained testicle. Laparoscopy belongs to a branch of surgery called minimally invasive surgery. The advantage that it offers is completion of a procedure through very small incisions, using specialized instrumentation, that leaves the patient at low-risk for post-operative pain and complications. Consequently, the surgery can be done during a very short hospitalization (two days) and with rapid return to normal use. In most horses on which we perform laparoscopy, only an intra-abdominal testicle can be removed by this method, but this is where most retained testicles appear to be located. The laparoscopic cryptorchidectomy can be performed as a standing procedure or with the horse under general anesthesia, and the surgeon can discuss the advantages and disadvantages of each. If the testicle is not in the abdomen, but in the inguinal canal, we can make a surgical approach to this location also. In some horses, an ultrasonographic examination can be used to determine if the testicle has been arrested in the inguinal canal.

The question often arises as to whether or not a retained testicle will descend in time. In many young horses, the small immature testicle cannot be palpated easily, although it might very well be close to the scrotum. In such cases, the testicle will get larger as it matures and become more palpable, leading to the erroneous impression that it descended in time. There are many horses in which a testicle cannot be palpated in the scrotum, but when they are sedated or anesthetized for surgery, the horse becomes sufficiently relaxed to allow the testicle to drop down and be obvious. Then a routine castration is performed on that testicle.

Very serious ethical issues can arise with cryptorchidism and horse owners need to be aware of this. A horse with unilateral (one-sided) cryptorchidism should not be castrated on the descended side without removing the retained or cryptorchid testicle at the same operation. Removal of the descended testicle only creates the outward appearance of a gelding. These horses can eventually end up in the hands of a new owner who is unaware of the history, but notices that the horse has stallion-like behavior. There are a number of tests that we can perform that will establish that the horse indeed has a retained testicle. However, now the new owner has to bear the expense of having this horse undergo a cryptorchidectomy and the surgeon may not be able to determine which side has the retained testicle.