Castration is the most common surgical procedure that we perform – in our practice geldings outnumber stallions somewhere in the region of 100 to 1!  It is usually performed at a young age, often less than a year old, as long as both testicles have descended.  The procedure is quick and relatively simple, although for those with a queasy disposition it can appear gruesome!  There are two methods of performing a castration – either under standing sedation, or under general anaesthesia.  In most cases the standing method is used due to the risks of a general anaesthetic.  We would recommend castration under general anaesthetic in older animals, donkeys and certain draught breeds.  Castrations are ideally performed in the winter months, when there are few flies around.



We normally perform castrations in the morning, and ideally the horse should be kept in overnight.  This is mainly to prevent them from covering themselves in mud overnight.  Food and water can both be provided as normal.  There are some preparations you can make to help everything run quickly and smoothly:

  1. Have a bucket of hot, clean water available
  2. Make sure your horse’s bedding is clean – straw is better than shavings
  3. Have the horse’s passport with you

Ideally your horse will have already been vaccinated against tetanus, but in young colts this may not be the case.  We will give tetanus anti-toxin to provide immediate protection, and often start their vaccinations at the same time. However, it is preferable to have the vaccinations up-to-date as this is safer for the horse but also in view of the cost of tetanus antitoxin!

The vet will then examine your horse, making sure that heart and lungs are healthy so there are no extra risks of sedation, and ensuring that two testicles are present.  An anti-inflammatory injection will often be given prior to the procedure, as it is more effective if given beforehand.  Your horse will then be sedated quite heavily so they cannot feel the procedure.

After an initial scrub the scrotum and surrounding area, local anaesthetic will be injected into each testicle to numb the area.

A thorough preparation of the scrotum will be performed with antiseptic scrub, to make it as sterile as possible.

The Castration

The vet will then remove the testicles through two incisions, one for each testicle.   An instrument called an Emasculator is used to clamp the testicular artery; this is left in situ for approximately 1-2 minutes per testicle to allow a clot to form. There is likely to be some bleeding, but you are not required to watch! The bleeding at this point is commonly a “drip-drip-drip”; this is quite normal because of the incision that has been made through the skin.


Looking after your horse after his big day is vitally important to avoid pain, swelling and infection.  He will remain sleepy for a couple of hours from the sedation, and cannot have anything to eat in this time, although water should be available.  If a horse is allowed to eat too soon following sedation, there is a risk that the food will be inadequately chewed and not enough saliva will be mixed with it. This causes a dry bolus of food to be stuck in the oesophagus (food pipe); this is called “choke” and avoiding feeding until after a few hours will help to prevent it.

When he is fully awake, he should remain in his stable until the next morning.  This period of standing still allows blood clots to form in the cut arteries and veins, and prevents bleeding from occurring.  The next morning turnout is ideal, although in many cases this is not available, as at this stage he will still be able to successfully cover mares!  Theoretically as a result of live sperm still remaining in the “tubes” leading from the testes to the penis (the vas deferens) it may be possible for a recently castrated gelding to successfully cover a mare. Sperm may survive for up to a week!!

If turnout is not possible, then walking out in hand should be done for a minimum of 15-30 minutes twice a day.  Approximately week after castration, your horse will no longer be able to impregnate a mare but hormone levels may take 4 weeks to subside. Many geldings, particularly if they have been castrated when sexually mature, may retain some of the characteristics associated with a stallion.


In all cases we will prescribe a course of anti-inflammatory and pain relieving medication, usually phenylbutazone (“bute”).  This is essential to keep swelling down, and to stop your horse from becoming painful.  Your vet may also choose to prescribe antibiotics, depending on the time of year, and what degree of sterility was achieved during the surgery.


Serious complications from castrations are not common, but there are 5 things to be aware of:

  1. Bleeding
    • There is likely to be some bleeding from the site for up to 48 hours after the surgery, this is normal.
    • You should always be able to “count the drips”.  Blood flow faster than this needs veterinary attention.
  2. Swelling
    • Some swelling is normal, up to 3x the normal size of the scrotum.
    • This will reach a peak 3-5 days after surgery, and then gradually decrease.
  3. Infection
    • Infection of the wounds will result in extra pain and swelling, and often a pus-like discharge.
    • Regular exercise to encourage drainage is key to preventing infection, along with strict fly control measures.
    • If you suspect infection, then call us immediately.
  4. Exposed Tissue
    • Occasionally small pieces of tissue can hang out through the wounds, these require veterinary attention.
    • Usually this is a small piece of the covering of the testicle, and is easily removed.
    • Extremely rarely, intestines can emerge through the wound.  This will look like a bunch of sausages.  If you see this then immediately push them upwards with a wet towel and contact us.  This is an extraordinarily rare occurrence.
  5. Persistent Stallion-like Behaviour
    • Some horses, especially those castrated when older, or those who have done any covering, will retain their stallion-like ways even when castrated.
    • This is normally due to learned behavioural responses, and needs careful counter-training.