Horse Side Vet Guide ®

Equine Health Resource

Penis Dropped, Will Not Retract, or Persistent Erection

Code Red - Call Your Vet Immediately, Even Outside Business Hours

Code Red - Call Your Vet Immediately, Even Outside Business Hours

  • If this condition lasts for more than several hours.

Intact and normal nerve and penile muscle function must exist for the penis to properly retract.

The most common cause of being incapable of penis retraction (over hours to days) is a rare reaction to acepromazine (“ace”) tranquilizer. This condition may also be caused by traumatic injury to the penis or sheath, damage to the nerves that are responsible for retracting the penis, and a variety of rare neuromuscular diseases.

Horses with systemic illnesses or who are in abdominal pain (colic) will often drop their penis during the illness or episode. In these cases, this condition resolves when the abdominal pain goes away. Sedation with a variety of drugs causes temporary dropping of the penis.

Whatever the cause, it is critical that horses with this problem are treated promptly. The longer the penis is left dropped, the more swelling and further damage occurs. If caught early, the problem is more likely to be resolved.


Assess your horse’s general health using the Whole Horse Exam (WHE) and share your findings and concerns with your vet, who will try to identify the underlying cause of this condition. Depending on the cause, some horses will recover function while others do not.


It is very important that conditions causing this observation are treated immediately by your vet. If the penis stays extended for long periods, it becomes swollen, painful, inflamed and more difficult to retract. Your vet considers the cause and provides nursing care and a treatment plan to maximize the likelihood of return to function.

Author: Doug Thal DVM Dipl. ABVP


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