What you see. The starting point for addressing any equine health related issue is your observation.


Sheath Swelling or Enlargement


The sheath is made up of soft and loose folds of tissue that allow the penis to drop and retract. Because of its many loose folds and its location on the lowest part of the body, it swells readily as a response to many conditions. The sheath also often becomes very fatty in overweight and insulin resistant horses. Sometimes distinguishing between a fat sheath and a swollen sheath can be difficult.

Sheaths also swell as a result of being "dirty." Horses with large beans (accumulations of secretions at the end of the penis) and large accumulations of sheath smegma (normal pasty secretion) often swell. Horses that urinate into their sheaths tend to have dirtier sheaths and more problems with swelling. Trauma, skin allergy and irritation as well as insect stings are examples of conditions that cause sheath swelling by irritation to the outer skin.

Sheath and penis skin infections and tumors cause swelling by irritation of the internal, hidden tissues. Commonly, injuries to the abdomen and even the upper limbs can cause local swelling that spreads over a distance through tissue planes and ultimately fills the sheath. Finally, the sheath is an indicator of general disease states such as low blood protein and vasculitis (inflammation of blood vessels that allow them to leak fluid into the tissues).

  • Code Red

    Call Your Vet Immediately, Even Outside Business Hours
    • If the swelling is large, painful or growing rapidly.
    • If the results of the Whole Horse Exam (WHE) in the resting horse indicate fever (Temp >101F/38.3C) or heart rate greater than 48 BPM.
  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.
    • If the swelling is mild or moderate, and not increasing rapidly.
  • Code Yellow

    Contact Your Vet at Your Convenience for an Appointment
    • If you consider this a chronic and relatively mild problem that is not changing rapidly.
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.

your role


What To Do

Assess your horse's general health using the Whole Horse Exam (WHE), paying attention to attitude and appetite, as well as the outside of the sheath in an attempt to determine the general cause of the problem. Pay particular attention to the appearance of the penis when the horse drops to urinate. Look for masses and reddening. Talk to your vet about symptomatic treatment you might administer until they can determine the underlying cause.

What Not To Do

Do not use disinfectants or harsh soaps on the sheath without your vet's guidance. It will only make the problem worse.

your vet's role

Sheath swelling can indicate local sheath problems like trauma and smegma accumulation, but it can also be a sign of body-wide disease. For that reason, your vet will probably start by determining your horse's general health with a careful physical exam. With body-wide (systemic) disease severe enough to cause sheath swelling (conditions like heart disease and vasculitis), there should also be other signs of disease detected on the physical exam. Keep in mind that your vet may want to use tranquilization to drop the penis to allow a thorough exam of the penis and sheath.
Questions Your Vet Might Ask:
  • How old is the horse?
  • What is the horse's age, sex, breed and history?
  • Is the horse eating, drinking and urinating normally?
  • When did the horse last look normal?
  • When did you first notice the swelling?
  • Do you notice any abnormalities of the penis or sheath?
  • Do you notice a growth, mass or wound associated with the penis or sheath?
  • Is the horse a stallion or a gelding?
  • What are the results of the Whole Horse Exam (WHE)?
  • Do you routinely clean the horse's sheath?
  • Are there noticeable skin lesions, crusts or scabs in the area?
  • Do you notice insects bothering the horse?

Diagnoses Your Vet May Consider

The cause of the problem. These are conditions or ailments that are the cause of the observations you make.

Very Common
Less Common
more diagnoses

further reading & resources


Helpful Terms and Topics

Written, reviewed or shared by experts in equine health

Author: Doug Thal DVM Dipl. ABVP