Cryptorchidism refers to the absence of one or both testicles in the scrotum of a stallion. It is a relatively common developmental disorder in horses and can occur in all horse breeds. These stallions are also colloquially referred to as "Klopp-, Spitz- or Urhengste" (clop, pointed or original stallions). Since the majority of cryptorchid stallions are infertile, this condition also has economic significance in relation to horse breeding.
Normally, the testicles descend from the abdominal cavity into the scrotum within 30 days before and up to about 10 days after the foal is born. This is due to the lower temperature outside the body, which is necessary for sperm production. The descent of the testicles is triggered by mechanical and hormonal factors.
Various factors can lead to a disruption of testicular descent. These include hormonal disorders, a gonadal cord that remains too long, adhesions to the kidney, and tumor or cyst formation. Although the hereditary nature of the disease has not yet been scientifically proven, it is highly likely.
Depending on the location of the undescended or incompletely descended testicles, three forms of cryptorchidism can be distinguished. One or both testicles may be affected.
In inguinal cryptorchidism (affecting the groin area), a small, usually underdeveloped testicle lies in an incomplete tunica vaginalis sac in the inguinal canal, which may also be palpable from the outside. In abdominal cryptorchidism (affecting the abdominal cavity), the missing testicle cannot be felt from the outside; it lies completely in the abdominal cavity. In some cases, the veterinarian can feel such an abdominal testicle during a rectal examination. Due to the higher temperature and altered blood circulation, these testicles are also small, underdeveloped, flaccid, do not produce sperm, and are prone to degeneration. However, since sex hormones continue to be produced, secondary sexual characteristics and sex drive are preserved.
It is not uncommon in horses for the testicle to be located in the abdominal cavity, but the epididymis and vas deferens to be located in the inguinal canal, in which case the condition is referred to as incomplete abdominal cryptorchidism.
Bilateral cryptorchids are infertile (= sterile), whereas unilateral cryptorchid stallions produce significantly less sperm but are still fertile. However, due to the high probability of the condition being hereditary, these animals should not be used for breeding.
In many cases, cryptorchid stallions are easily identified by the obvious absence of one or both testicles in the scrotum. Since hormone production is not impaired in cryptorchidism, cryptorchid, infertile stallions exhibit normal sex drive and stallion-typical behavior. Older cryptorchids often behave aggressively and viciously, which can make handling them considerably more difficult.
If you suspect that your stallion is cryptorchid or your gelding suddenly exhibits atypical stallion behavior, take him to a veterinarian as soon as possible.
Since diagnosis is not always straightforward, your veterinarian will often ask you for a detailed preliminary report, as information about the breeder, previous owners, and any attempts at castration is very important for the further course of the examination. They will then carry out a thorough clinical examination. As part of this examination, they will carefully palpate the entire scrotum from the outside and, depending on the case, also perform a rectal examination. In some cases, they will be able to make a diagnosis at this stage, but not all undescended testicles can be located in this way.
In animals that are believed to have been castrated but exhibit stallion behavior, castration wounds must be examined very carefully. Another method of detecting a missing testicle is ultrasound, which can be performed both internally via the rectum and externally in the groin area.
In cases where the diagnosis remains unclear, a blood test to determine testosterone levels can be used to distinguish between a stallion and a gelding. Stallions and cryptorchids have high testosterone levels, while geldings have very low levels.
Hormone treatment to stimulate testicular descent is not possible. To prevent tumorous degeneration, cyst formation, and undesirable behavior, cryptorchid stallions should be castrated at an early age. In cases of unilateral cryptorchidism, both the testicle located in the scrotum and the undescended cryptorchid testicle must be surgically removed.
Depending on the location of the testicle(s), the veterinarian has various surgical options, some of which can be performed on a standing horse and some of which are minimally invasive using laparoscopy (keyhole surgery).
The operation should be performed in a suitably equipped equine clinic where the horse can be monitored for the first few days after the operation. Your veterinarian will discuss with you which method is most suitable in each individual case.
Apart from the fact that the horse can no longer be used for breeding, the prognosis for its use as a riding horse is good.
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