A Daily reader seeks advice about breeding her cryptorchid stallion.

Question:

Would it be possible to get information on cryptorchidism in stallions? I have a stud colt that I would like to breed, but he only has the left testicle down. Is this a genetic trait that can be passed on to the next generation? I read in two different sources that he can breed or he cannot breed. I don’t know which one is the truth. Thank you. Candice Wright

Answer:

Although not a common condition in the horse, cryptorchidism can be a serious dilemma if it occurs in a stallion. It is considered an undesirable trait and is defined as a stallion having less than two visible testicles descended into the scrotum. Stallions so affected are commonly referred to as “cryptorchids,” “rigs,” “ridglings,” “originals” or “high flankers.” Retention of one testicle is most common and occurs nine times more frequently than retention of both testicles. If the left testicle is retained, 75 percent of the time it will be retained in the abdomen. Whereas, if the right testicle is retained, it will be in the inguinal canal or just under the skin 60 percent of the time. Although most veterinarians believe cryptorchidism is an inherited condition, the gene that causes it has not yet been identified.

Because cryptorchidism is not a fatal condition, owners are often confused as to why veterinarians and breed associations consider the condition a defect and recommend castration of affected horses. There are a number of reasons; the most significant is that cryptorchids are not genetically normal horses and the retained testicle, although capable of producing testosterone, cannot produce live sperm and, therefore, affected horses have reduced fertility. A second problem is, until proven differently, it is an inherited condition and male off spring may also have the condition, perpetuating the abnormality. The third problem with cryptorchids is that removal of the retained testicle from the inguinal ring or abdomen requires expensive and risky surgery that most horse owners would prefer to avoid. Finally, as cryptorchid horses grow older, the undescended testicle has a higher risk of developing cancer than a normal descended testicle.

Hope this helps.

Dr. Tom R. Lenz of AQHA Corporate Partner Fort Dodge Animal Health

For more advice from Dr. Lenz, check out AQHA’s popular “Your Horse’s Health” DVD.

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