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162 – June, 2016


By William Given

Monorchidism is an all-too-common condition among male dogs. It refers to the defect in which one of the dog’s testes remains undescended. This canine defect has been recognized for many decades. Even by selectively breeding only males with two normally descended testicles, this defect may be exhibited with relative frequency in their progeny.

Many of us in the sport of purebred dogs and in the breeding community have for many, many years used the term “monorchidism” when referring to a male dog that has one tes- ticle undescended. The correct scientific term is “unilateral cryptorchid.” A dog with both testes undescended would prop- erly be referred to as a “bilateral cryptorchid.” The scientific meaning of the word monorchid is a dog in which one testis is entirely absent and not simply retained in his abdomen or in the inguinal canal. Cryptorchid is derived from the Greek for “hid- den” “testicle.”

The Physiology of Descent

The process of testicular descent in canines occurs in three stages. In step one, the testes move from the abdominal cavity into the ring of the internal inguinal canal. During step two, the testes travel through the inguinal canal; and step three consists of the descent of the testes from the inguinal canal into the scro- tum. It should be noted that the descent may fail at any point in one of the three phases. Normally, three or four days after birth the testes complete their passage through the inguinal canal and arrive at their final position in the scrotal sack sometime be- tween two weeks and one month of age.

If a testis begins to enlarge prior to its entry into the internal inguinal ring or if for any reason entry is delayed, the testis may be retained in the abdomen. If it begins to enlarge after entering the internal inguinal ring but prior to exiting the external inguinal ring, then the normal testicular passage through the inguinal canal can be halted, and the dog may become an inguinal cryptorchid. The right testis is more commonly retained than the left. This is possibly due to its starting position in the abdomen.

There appears to exist several abnormalities of development which may have an impact on the male pup during the time he is in utero. Any one of these could cause the physiological in- terference of a testis in the course of its descent. Additionally, it reasons that the genes controlling each of these areas, and the tissues of which these areas are composed is directly involved in the normal development and descent of the testes.

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162 – June, 2016

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