In animals, if bilateral cryptorchidism, results in sterility.
In horses cryptorchids may be spoken of as “ridglings,” “rigs” or “originals”.
Unilateral cryptorchidism is more common and usually results in near normal fertility because of normal sperm production from the testis located in the scrotum.
The term “monorchidism” is incorrect.
Cryptorchidism or incomplete descent of the testis or retention of the testis occurs in all domestic species. But seen most commonly stallion, boars, dogs less commonly in rams and bucks, uncommonly in cattle, and rarely in cats.
The undescended testis may be located anywhere from just caudal to the kidney to within the inguinal canal.
Many abdominal testes are located close to the internal inguinal ring.
Occasionally testes may be located ectopically under the skin of the ventral caudal abdomen, alongside the penis, or rarely in the femoral canal or the perineal region. This is more commonly the case in male pseudohermaphrodites where no scrotum is present.
In some cases where the testis is retained in the inguinal canal, it will descend spontaneously into the scrotum in a few months to a year after birth.
In a few cases in colts, testes may be descended into the scrotum at birth and later become cryptorchid and located in the inguinal canal.
All retained or cryptorchid testes are small, soft and flaccid weighing in the horse 25 to 131 gm. Normal descended testes usually weigh 170 to 325 gm.
No spermatozoa are produced by the retained testis but well-developed or degenerate seminiferous tubules may be present.
Spermatogenesis is completely inhibited by the elevation of the temperature of the affected testis.
The interstitial or Leydig cells are not affected so sexual activity is normal or even exaggerated in bilateral cryptorchids.
Cryptorchid animals should never be used for breeding.
Cryptorchidism in the horse is inherited in a dominant manner while in the other species it is a recessive trait.
In dogs cryptorchidism is seen most commonly in the brachycephalic breeds including: Boxers, Pomeranians, Dachshunds, Sealyhams, Cairn Terriers, and also in Whippets, Chows, Cocker Spaniels, Poodles, and others.
In some dogs the testes don’t descend till near puberty.
Possibly because dogs are maintained intact for many years, retained testes are predisposed to neoplasms.
Sertoli cell tumors and seminomas in undescended testes tend to be more malignant.
These tumors affected the retained or abdominal right testes more frequently than the retained left testes.
Tumors of undescended testes in man occurred 50 times more often than tumors of scrotal testes. Hence, early removal of undescended testes is recommended.
Cryptorchidism in swine is a monogenic sex-limited recessive. To eliminate this condition in swine or others species all parents of cryptorchid animals should be discarded as breeders.
The incidence in swine reach 1 to 2 percent in some herds.
Treatment of cryptorchid animals, especially those where breeding is to be considered, should be discouraged.
Orchiopexy has proven to be a failure in producing satisfactory spermatogenesis.
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