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Equine Health Resource

Stallion-Like Behavior in Gelding

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Code Yellow - Contact Your Vet at Your Convenience for an Appointment

    A fairly common complaint in veterinary practice is the gelding that acts like a stallion. These geldings may mount mares, act possessive of mares in a band, achieve an erection, or pursue mares even while being ridden. They may be generally more aggressive and harder to handle than a typical gelding. They may or may not show stallion physical characteristics like heavy muscling of the neck and jowls. Stallion behavior is caused almost exclusively by the presence of testosterone.

    In most cases, the cause of stallion-like behavior actually DOES relate to the presence of testosterone in the circulation. A normal gelding should have a very low blood testosterone level. The term “Proud Cut” refers to a horse that has been gelded (or has no visible testicles) but some testosterone producing tissue still exists. This should not happen if a gelding has been properly castrated. A retained testicle is referred to as “cryptorchid”, and occasionally a horse will have the visible testicle removed and the retained testicle left in. This is considered unethical and negligent.

    In rare cases, there is no hormonal explanation for the behavior (the horse is found to have very low levels of testosterone). Firm handling and training will be necessary to counteract this tendency. The gelding may also need to be managed separate from mares.


    Always be extremely cautious of a gelding that exhibits stallion-like behavior. They can be dangerous, and some are likely to bite. Consider whether you notice stallion-like physical characteristics in the horse, like heavy muscling of the neck, large jowls. Get your vet involved right away, to perform laboratory tests, looking for testosterone. If it turns out that there is high testosterone, it is smart to have surgery performed to remove it.


    Your vet can easily assess testosterone level by using a blood test. In some cases, the testosterone levels may not clearly differentiate the presence of testosterone producing tissue from lack thereof. In these cases, a lab test called “HCG stimulation” is used. If significant testosterone is found, then other diagnostic tests like ultrasound will be used to help locate the testicle. In some cases, a surgeon will simply have to explore both left and right inguinal rings in order to find and remove an internal testicle.

    Author: Doug Thal DVM Dipl. ABVP


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