Cryptorchidism is a condition in which one or both testicles are not located in the scrotum.  Dr. Bill Pickett from Colorado State indicates in the Horse magazine that in a normal colt, testicles are initially in the abdominal cavity, and then between 30 days before birth to 10 days after birth they should descend through the inguinal canal and into the scrotum.  However, sometimes the testicle does not descend, a condition called cryptorchidism.  There are multiple theories as to the cause of cryptorchidism but regardless, if the testicle is in the inguinal canal, there are some hormone treatments that have been reported to be effective at causing the testicle to enter the scrotum.  However, if the testicle is in the abdomen it will not descend regardless of treatment and will require surgical removal.  

So, if the testicle is in the inguinal canal, hormonal therapy can be tried and Dr. Steven Conboy from Kentucky indicates if he has a stallion that has an undescended testicle at 12 months of age, he will administer an injection of human chorionic gonadotropin twice weekly for four to six weeks.  He reports that on a standardbred farm, this process was effective in 58 percent of the colts at allowing descension of the testicle, while only six percent descended without the drug.  Another drug used, GNRH, is reported to have a similar effect. 

The real question is if these injections are effective, should a cryptorchid horse be used for breeding?  Although most veterinarians believe the condition is hereditary, this has not been scientifically proven to be the case.  Research is being performed by gene mapping to further clarify the issue but at this time, it is really up to individual horse owners to determine if they want to breed a stallion that was born as a cryptorchid.