About Us    Donate    

Large Animal Topics

What is a Diplomate?
The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery.

Bookmark and Share

Text Size

Current Size: 100%

Cryptorchidism (Undescended Testicles) in Horses

The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery. Only veterinarians who have successfully completed the certification requirements of the ACVS are Diplomates of the American College of Veterinary Surgeons and have earned the right to be called specialists in veterinary surgery.

Your ACVS board-certified veterinary surgeon completed a three-year residency program, met specific training and caseload requirements, performed research and had research published. This process was supervised by ACVS Diplomates, ensuring consistency in training and adherence to high standards. After completing the residency program, the individual passed a rigorous examination. Only then did your veterinary surgeon earn the title of ACVS Diplomate.


Cryptorchidism means, "hidden testes" (crypt = hidden, orchid = testes). Common terms for pets with this condition include rig, ridgling, original or high flanker.

This term describes the condition in which one (unilateral) or both (bilateral) testicles do not descend normally into the scrotum. Unilateral cryptorchids are usually fertile, while bilateral cryptorchids are generally sterile. The testes may be retained anywhere from the abdomen to the inguinal canal, the normal passage route into the scrotum (Figure 1). A single cause of equine cryptorchidism has not been established and contributing causes remain obscure. The condition is likely the result of a complex combination of genetic, hormonal, and mechanical factors.

Prevalence of left and right testicular retention is nearly equal, though retained left testes are more often in the abdomen while the right retained testicle is more often in the inguinal canal. All breeds of horses may be exhibit cryptorchidism, but there is a higher frequency in Quarter Horses, Saddlebreds, Percherons, and ponies. The condition is considered heritable, so affected pets should be castrated to help prevent continuation of this congenital defect and for safety reasons (although a testicle is undescended, it still produces male hormones leading to characteristic stallion behavior). Also, many breed associations do not allow registration of cryptorchids.

Signs and Symptoms: 

Cryptorchid horses usually exhibit standard stallion behavior, but visibly/palpably lack one or both scrotal testicles.

  • Immature horses may be undetected until they are examined just prior to routine castration.
  • Mature horses with no detectable testes that behave like stallions may be:
    • Bilateral cryptorchid
    • Unilateral cryptorchid with the descended testes previously removed
    • Geldings with stallion-like behavior (castrated later in life +/- previous breeding stallion).

Monorchidism (complete absence of one testicle) is rare in the horse and should only be considered after extensive testing and, potentially, surgical exploration.


You primary care veterinarian may recommend performing the following diagnostics:

  • Combination of external and rectal palpation +/- ultrasonographic examination to locate a testicle within the abdomen or inguinal canal.
  • Blood tests when incomplete background information or absence of palpable testicles (~95% accurate, both tests should be performed if either is inconclusive).
    • Testosterone levels: Measured in the blood before and after administration of human chorionic gonadotropin (hCG).
      • Stallions and cryptorchids have higher levels of testosterone and levels of the hormone increase after hCG administration.
      • Castrated horses have low levels of testosterone and levels do not increase with hCG.
    • Conjugated estrogen levels:  Typically, levels are higher in horses with testicular tissue, and a single measurement can often identify cryptorchids.
      • Unreliable in horses younger than 3 years and in donkeys.

An ACVS board-certified veterinary surgeon should perform the identification and surgical removal of undescended testicles. The testicles are often smaller than normal and may not be formed correctly. Given the relatively large, crowded area in which they may be located, the job of finding and safely removing a wayward testicle can be a challenge. Veterinary surgeons trained according to the standards of the American College of Veterinary Surgeons have specific knowledge and skills for diagnosis and treatment of cryptorchidism in the horse.

  • Surgical removal of both testicles:
    • Standard surgical approach: With the horse on its back under general anesthesia, an incision is made, generally on the underside of the belly around the area of the scrotum. The testicle is located and manually removed from the abdomen or inguinal canal.
    • Laparoscopic approach: With the horse standing or with the horse on its back under general anesthesia, using a camera and specialized equipment. With the horse standing, the abdomen is distended with sterile gas, and a camera is inserted into the abdomen through a small incision in the flank. Once the testicle is located, further small incisions are made to pass instruments into the abdomen and remove the testicle.

With either approach, meticulous attention is paid to ensure that the blood supply to the testicle is securely closed off prior to removal to prevent potential bleeding.

Aftercare and Outcome: 

Initial care after surgery usually consists of stall rest with hand walking. Unlimited exercise is gradually resumed after approximately 10 days to two weeks. Any sutures are typically removed around 10-14 days after surgery. Following laparoscopic surgery, the aftercare period is much reduced and horses can resume their activities after the first 72 hours. As with any castration procedure, after surgery take appropriate handling and socialization measures.

Complications may include:

  • Anesthetic complications
  • Excessive hemorrhage
  • Bowel damage
  • Infection
  • Post-operative swelling
  • Incision breakdown
  • Continued stallion-like behavior

Though hormone levels dissipate almost immediately after testicle removal, learned behaviors often take a period of time and training to change.

Content Theme: 

This Animal Health Topic was written by and reviewed by Diplomates of the American College of Veterinary Surgeons.  Any opinions stated in this article are not necessarily the official position of the American College of Veterinary Surgeons.

The American College of Veterinary Surgeons recommends contacting an ACVS board-certified veterinary surgeon or your general veterinarian for more information about this topic.

To find an ACVS Diplomate, visit www.acvs.org/find-a-surgeon.