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' Undescended Testicles Not Uncommon In Stallions, But Complicated For Owners

With very few exceptions, a male horse has two testicles, although they may sometimes be difficult to find. The percentage isn't high, but most people who have raised a number of horses have experienced the sit­ uation in which one or two testicles cannot readily be found in a colt or stallion. This requires a different approach for castration. "Cryptorchidism is the definition of hidden testes, which is the condition in which one, called unilateral, or two, known as bilateral, testicles do not descend normally," according to Dr. Mandi Lopez, a veterinarian and assistant professor at Louisiana State University School of Veterinary Medicine, Baton Rouge. Common terms for animals with the condition include rig, ridgling, original or high flanker, although cowboys often use more indelicate terminology. "In a cryptorchid horse, the testicle, which forms in the abdomen of the fetus, does not migrate out of the body and into the scrotum," Lopez described. "The testicle may be retained anywhere from the abdomen to the inguinal canal, the normal passage route into the scrotum," she related in scientific terms. Prevalence of left and right testicular retention is nearly equal. However, Lopez clarified, "Left testes are more commonly found in the abdomen, while right testes are retained in the inguinal canal." A testicle that is undescended still produces male hormones leading to characteristic stallion behavior. Regarding fertility, the veterinarian explained, "Unilateral cryptorchids are usually fertile, while bilateral cryp­ torchids are frequently sterile." "The condition is considered heritable, so an affected animal should be castrated to help prevent continua­ tion of this congenital defect, as well as for safety reasons," Lopez emphasized. All male horses can have undescended testicles, but there is a higher frequency in certain breeds, includ­ ing the American Quarter Horse, Percheron, American Saddle Horse and ponies. Some breeds do not allow registration of cryptorchids. A single cause of undescended testicles has not been established. "Contributing causes remain obscure, but based on available information, the condition is likely the result of a complex combination of genetic, hor­ monal and mechanical factors," Lopez recognized. Immature horses with undescended testicles may be undetected until they are examined just prior to cas­ tration. With yearling, and sometimes even older, male horses, longtime horsemen often claim: "His testicles haven't come down yet. We'll have to wait longer." However, Lopez concurred, "We generally expect to be able to locate the testicles when a colt is weaned at about six months." "A combination of external and rectal palpation is sometimes required with tranquilization needed in some situations, so the testes will drop enough to be palpated," she added. Mature horses with no detectable testes, yet that behave like stallions, may be bilateral cryptorchids, uni­ lateral cryptorchids with the descended testes removed, or even with stallion-like behavior. Diagnosis of cryptorchdism in horses that don't have palpable testes is typically accomplished with blood tests. "Monorchidism, meaning complete absence of one testicle, is rare in horses, and should only be considered after extensive testing, and, potentially, surgical examination," stressed Lopez, who in "hundreds of cases" has never seen a horse that didn't have testicles. Treatment for cryptorchidism is surgical removal of the testicle. "There are no known drugs for treatment of cryptorchidism at this lime," Lopez clarified. Removal should be performed by a trained veterinary surgeon. "Given the relatively large, crowded area in which they may be located, the job of finding and safely removing a wayward testicle can be a challenge," Lopez contended. The standard procedure with the horse on its back is done under general anesthesia. A laparoscopic approach can be done with general anesthesia, or with the horse standing under sedation, and the surgical area densensitized. "The approach taken depends on the preference of the surgeon as well as the age and temperament of the horse," Lopez commented. "When the standard surgery is performed, an incision is made on the underside of the belly around the area of the scrotum," she detailed. "The testicle is located and manually removed from the abdomen or inguinal canal." Attention must be paid to ensure that the blood supply to the testicle is closed off prior to removal to prevent potential hemorrhage, Lopez noted. Generally, the undescended testicles are much smaller than those properly descended. While myth has indi­ cated that the testicle might be as small as a marble or even an eraser, Lopez indicated that they are gener­ ally one-half to one-quarter the size of a normal testicle. Complications are rare for cryptorchid surgery, Lopez said, but they may include anesthetic complications, excessive bleeding, bowel damage, infection, post-operative swelling, incision breakdown, and continued stal­ lion behavior. Initial care after surgery usually consists of stall rest with hand walking. Unlimited exercise is gradually resumed after approximately 10 days. "Though hormone levels dissipate almost immediately after testicle removal, learned behaviors often take a period of time and training to change," Lopez concluded.

This photograph of an undescended testicle (black arrow) was taken during Japroscopic (standing) surgery on a cryptorchid (undescended testicle) horse. The testicle is resting in the abdomen next to the inguinal canal (white arrow). In a normal horse, only the spermatic cord (black arrowhead) would be seen passing through the canal, and the testicle would be located in the scrotum.