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


Small or Different Size Testicles


Small or differently sized testicles in stallions and growing colts can result from a variety of causes. Small testicles may result from congenital abnormalities or testicular degeneration caused by a variety of conditions. It may or may not be associated with infertility.

Differently sized testicles may result from a recently dropped (cryptorchid) testicle. Large testicles can result from infection, inflammation and tumors. The question always is which of the two testicles is normal?

Swelling of the scrotum on one side is an observation that can be caused by a list of potential conditions and is discussed in a related observations fast fact "Swelling of Scrotum in Stallion". Scrotal trauma is common in breeding stallions and is the most common reason for scrotal swelling.

Viral diseases such as EVA and EIA can also cause a testicle to swell.

  • Code Orange

    Call Your Vet at Their First Available Office Hours
    • If there is swelling and pain associated with this problem.
    • 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 Yellow

    Contact Your Vet at Your Convenience for an Appointment
    • If the results of the Whole Horse Exam (WHE) suggest the horse is otherwise normal.
    • If the area does not seem to be painful.

your role


What To Do

In all cases, assess your horse's general health using the Whole Horse Exam (WHE), and share your findings and concerns with your vet. Pay particular attention the presence or absence of pain response when the area is palpated. Also look for heat and/or swelling.

For breeding stallions, any change in the scrotum should be discussed with your vet immediately. For testicular diseases, time can be of the essence. Do not breed the stallion again until a full veterinary evaluation has been performed.

your vet's role

By looking and feeling, your vet should be able to determine which of the two testicles is normal. Further information can be gathered through the use of ultrasound, rectal palpation and other diagnostics.
Questions Your Vet Might Ask:
  • When did you first notice this problem?
  • How old is the horse?
  • How does the affected side compare to the normal side?
  • Is the area painful to pressure with your hands?
  • Does there seem to be heat in the area?
  • What are the results of the Whole Horse Exam (WHE)?

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
more treatments

Author: Doug Thal DVM Dipl. ABVP