A proud cut horse is a gelding that continues to act like a stallion after castration. The term traditionally describes horses that show aggressive, sexual, or dominant behaviors you wouldn’t expect from a castrated male. In most cases, the cause is retained testicular tissue that was never fully removed during the gelding procedure, a condition veterinarians call cryptorchidism. Somewhere between 2% and 12% of horses are affected by cryptorchidism, making this far from rare.
Why a Gelding Still Acts Like a Stallion
During normal development, a colt’s testes descend from the abdomen into the scrotum. In cryptorchid horses, one or both testes fail to descend fully. They can remain lodged in the abdomen or get stuck partway down in the inguinal canal near the groin. When a veterinarian castrates the horse, they may only remove the testes they can see and reach in the scrotum, leaving a retained testis behind.
That retained testis doesn’t produce viable sperm (the higher body temperature prevents it), but it keeps pumping out testosterone. A properly gelded horse has testosterone levels below 50 picograms per milliliter. A horse with a retained testis typically falls in the 100 to 500 range. A fully intact stallion sits between 800 and 2,000. So a proud cut horse is living with hormone levels two to ten times higher than a normal gelding, which is more than enough to drive stallion-like behavior.
Behaviors That Signal a Problem
Proud cut horses can look and act dramatically different from typical geldings. The hallmark behaviors include mounting mares, showing sexual interest by teasing or flehmen response (that curled-lip sniffing posture), achieving erections, and in some cases ejaculating, though they’re infertile. Beyond sexual behavior, these horses often display unpredictable aggression toward other horses and handlers. They may become territorial, difficult to manage in mixed herds, and generally harder to train and handle safely.
The severity varies. A horse with a single retained testis may show mild stallion tendencies that only surface around mares in heat. A horse with both testes retained and only partially castrated can behave almost identically to a full stallion. The key distinction is that these behaviors persist months or years after castration, long past the point when residual hormones from a normal gelding procedure would have cleared the system.
One Common Myth Worth Clearing Up
A widespread belief in the horse world holds that leftover tissue from the epididymis or spermatic cord can produce testosterone after castration. This isn’t true. The epididymis and spermatic cord of the horse do not produce testosterone. If a gelding is showing persistent stallion behavior, the cause is actual testicular tissue that was left behind, not remnants from surrounding structures. This matters because it changes the path forward: the solution is finding and removing that tissue, not simply waiting for residual hormones to fade.
How Veterinarians Confirm the Diagnosis
A blood test is the most straightforward way to determine whether a horse still has testicular tissue. The simplest approach measures testosterone from a single blood draw. Geldings fall below 50 pg/mL, while cryptorchid horses register between 100 and 500 pg/mL. Values between 50 and 100 are considered inconclusive and may require follow-up testing.
A newer and increasingly preferred option measures a hormone called anti-Müllerian hormone, or AMH. This hormone is produced exclusively by cells inside the testes. In properly gelded horses, AMH is undetectable. In horses with retained testicular tissue, even a single undescended testis, AMH shows up clearly in the blood. This makes it a reliable yes-or-no indicator of whether testicular tissue is present, without the timing complications that can affect testosterone readings (which fluctuate throughout the day and across seasons).
If a veterinarian wants additional confirmation, they may use a stimulation test that involves injecting a hormone to provoke a testosterone spike, then measuring the response. But for most cases, a baseline AMH or testosterone test is enough to distinguish a true cryptorchid from a gelding with behavioral issues.
Surgical Options and Recovery
Once retained testicular tissue is confirmed, the standard treatment is surgical removal. The approach depends on where the testis is located.
For testes retained in the abdomen, standing laparoscopic surgery has become the most common technique. In a large retrospective study of 70 cryptorchid cases, nearly 63% were handled this way. The horse remains standing and sedated while the surgeon uses a small camera and instruments inserted through the flank to locate and remove the retained testis. This approach offers excellent visualization, shorter surgical time, fewer complications, and faster recovery compared to traditional open surgery.
For testes stuck in the inguinal canal, an open surgical approach under general anesthesia is typically required. The horse is placed on its back, and the surgeon accesses the retained testis through an incision near the groin. This was used in about 37% of cases in the same study.
In all documented cases, the retained testis was successfully removed. Complete removal is important because leaving even a fragment behind can allow blood supply to reconnect and testosterone production to resume, perpetuating stallion behavior. After surgery, horses receive a short course of antibiotics and pain management for roughly three days. Most recover uneventfully, though recovery time varies depending on whether the procedure was laparoscopic (shorter) or open (longer, with a healing incision).
When Behavior Outlasts the Hormones
Not every gelding that acts like a stallion has retained tissue. Some horses, particularly those gelded later in life after reaching sexual maturity, have deeply ingrained behavioral patterns that persist purely out of habit. These horses test normal on blood work, with testosterone and AMH levels consistent with a fully castrated male, but they continue mounting, posturing, or showing aggression.
This distinction is critical because the treatment path is completely different. A horse with retained tissue needs surgery. A horse with learned behavior needs consistent training, management changes (such as separating from mares), and time. Behavioral modification can be slow, and some habits may never fully disappear in horses that spent years as intact stallions before being gelded. Blood testing is always the first step to determine which category a proud cut horse falls into, since the management strategies diverge entirely from that point.
Health Risks Beyond Behavior
Proud cut behavior isn’t just a training inconvenience. Horses with retained testes face a slightly elevated risk of testicular tumors and torsion of the spermatic cord, a painful twisting that can cut off blood supply to the retained testis. The prevalence of incomplete castration among cryptorchid horses is notably high, reported at up to 41%, which means a significant number of horses with undescended testes end up only partially gelded. If you’re buying or managing a gelding that shows stallion-like behavior, testing for retained tissue is a worthwhile step that can prevent both behavioral problems and long-term health complications.