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


Swelling of Scrotum in Stallion


There is normal seasonal variation of scrotal size in stallions. During the breeding season, a stallion's testicles may naturally enlarge.

However, swelling of the scrotum (often worse on one side) can also be caused by a variety of health conditions. Scrotal trauma is common in breeding stallions and is the most common cause of scrotal swelling. Viral diseases such as EVA, as well as scrotal hernias and testicular torsion can cause a testicle to swell. Bacterial infection (orchitis) is another uncommon cause.

  • Code Red

    Call Your Vet Immediately, Even Outside Business Hours
    • If you feel the problem is severe or has come on suddenly.
    • If you notice signs of colic, along with this sign.
    • 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 problem is subtle or slowly changing.
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.
    • If the condition does not seem to be causing pain or other problem.

your role


What To Do

Assess your horse's general health using the Whole Horse Exam (WHE) and share your findings and concerns with your vet. For many of these conditions, time is of the essence. Do not breed the stallion again until a full evaluation has been performed.


Vets use clinical exam, and palpation of the scrotum to determine the cause of the swelling. In some cases, ultrasound and/or laboratory work may be helpful.

your vet's role

Questions Your Vet Might Ask:
  • Do you notice any signs of abdominal pain (colic)?
  • Does the horse's general health seem good to you otherwise?
  • What is the age and breed of the horse?
  • When did you first notice this problem?
  • Is the swelling only found on one side (asymmetrical), or is it similar on both sides?
  • Is it a testicle or the whole scrotum that feels enlarged?
  • Can you see drainage or a wound?
  • Has there been a traumatic incident that you know of?
  • Have you given any medications to the horse, what and when?
  • What are the results of the Whole Horse Exam (WHE)?
  • What are the results of the Whole Horse Exam (WHE)?
  • When was the stallion last bred?

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
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Treatments Your Vet May Recommend

A way to resolve the condition or diagnosis. Resolving the underlying cause or treating the signs of disease (symptomatic treatment)

Very Common
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Author: Doug Thal DVM Dipl. ABVP