Horse-breeding need-to-know information: Straight talk about cryptorchidism.
October 6, 2016
Fact: A colt's testicles can drop and then disappear when he is a weanling. A colt's testicles should be descended at birth, but when the horse is weeks or months old, they might not be visible because as the colt's body matures, the testicles might not be palpable in the scrotum. These are not true cryptorchids, as the testicles should descend normally by the time the horse is a 2-year-old.
Fact: A retained testicle can cause cancer. While cancerous growths in a retained testicle are rare, they're not unheard of. Increased temperature is often associated with the growth of tumors. Because the testicle is retained inside the body, it is exposed to higher temperatures, thereby increasing the risk of cancer.
Fact: A retained testicle cannot produce sperm. If the testicle is retained inside the abdomen, the scrotum cannot regulate the temperature of that testicle. Since the temperature inside the body is too high for sperm growth, the male will be sterile in that testicle.
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Fact: Cryptorchids have lower fertility. A stallion that only has one descended testicle only has one testicle to produce sperm, which automatically lowers the semen count for the stallion.
Fact: An undescended testicle is not necessarily painful for a horse. The most common form of cryptorchidism is the unilateral cryptorchidism, in which one testicle is retained and one testicle is normal. While the retained testicle can become predisposed to torsion, or twisting on its axis, because it doesn't have a scrotum to sit in, if this does not occur, there are no indications that a retained testicle causes pain or inhibits athletic performance.
Fact: Cryptorchidism is genetic. If you choose to breed your mare to a cryptorchid, the stallion owner should let you know about the stallion's condition and associated hereditary risks.
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Fact: Cryptorchids can be more difficult to castrate. While removing an undescended testicle is always a surgical procedure that can't simply be done on the farm, it's not as difficult as it used to be. With the development of laparoscopic procedures, a rigid arthroscope (a camera) is inserted through a standing horse's flank. Another hole is pierced for the instruments. The veterinarian can see what the camera sees through a monitor, and the horse has a much smaller incision on the flank to heal instead of a wound in his belly. This is much less invasive, however, it is still a more complicated procedure than a simple castration performed on a horse with two descended testicles.
Fact: There are three ways to check for cryptorchidism:
- Rectal palpation
- Transrectal ultrasound
- Hormone challenge testing
Fact: Cryptorchids are more aggressive than geldings. Whether retained or descended, testicles produce testosterone. Normal stallions and cryptorchid stallions produce the same amount of testosterone. Cryptorchid stallions that haven't been castrated will continue to show the same aggressiveness as a full stallion.