Paraphimosis is a condition of the penis in which it cannot retract. Generally, this occurs when the penis has been extended for a period of time and it swells, causing a tightening of the sheath around it that prevents retraction. Priapism is a term meaning persistent erection. Strictly speaking, that is a different problem but will be addressed here too.

Paraphimosis is most often caused by traumatic injury to the penis. Trauma to the penis is fairly common in breeding stallions, and is usually caused by a kick from a mare. Penile paralysis (or priapism) is also a rare side effect of certain tranquilizers, (phenothiazine tranquilizers like acepromazine). Anything causing nerve injury to the nerves that are involved in penis retraction can also cause paraphimosis. Horses that are severely debilitated or that have other disease may also have difficulty retracting the penis.

Regardless of the initial cause, there tends to be a vicious cycle of exposure leading initially to inflammation and swelling , leading to tightening of tissues around the penis, and less and less ability to retract.

The diagnosis of penile paralysis or persistent erection is clear. The underlying cause may be less clear and might involve diagnostics to rule out those conditions.

Treatment needs to be prompt and usually starts with careful veterinary examination to determine cause, and inspection of the penis and sheath for wounds or other injuries. These are treated as needed. The penis is usually cleaned and then an attempt is made at replacing it in the sheath. The problem is reducing the swelling and keeping it in place. There are a variety of slings that have been used to hold the penis in the sheath in these cases, as swelling reduces and retracting function hopefully returns. Other treatments include drugs to reduce pain and swelling, and topical medications.

In cases of severe nerve damage, penile paralysis may be permanent. In this case, penile amputation or other surgical approach may be advised.