Why Castrate?

We recommend castration (surgical removal of the testicles) of all colts and stallions unless they are specifically required for breeding.

There are several reasons, other than preventing unwanted pregnancies, why castration is recommended.

  1. It prevents masculine or aggressive behaviour which can be dangerous.
  2. It allows male horses to be turned out with company, which, being social animals, is important for their welfare.
  3. It prevents the risks of testicular trauma, or testicular cancer.
  4. It prevents the risk of life-threatening colic from intestines herniating through the inguinal canal.

When to Castrate?

Typically castration is performed from the spring of the yearling year. We prefer to castrate during the Spring or Autumn to avoid mud in winter and flies in summer, but the procedure can be carried out at any time of year if necessary. Castration is usually performed between 6-18 months of age.

The surgical procedure

The open technique

This is the routine method of castration used in the field for both standing castrations and those performed under general anaesthesia. The testicles are removed via two surgical incisions into the scrotum. The blood vessels and other tissues running from the testicle into the abdomen are crushed and cut. The vaginal tunic and scrotum are left ‘open’ for drainage.

The closed technique

This procedure takes longer and requires a clean operating theatre environment because the tissue layers are sutured closed after the testicles have been removed so the wounds cannot drain. This technique is more costly and is recommended for older or very large stallions, especially if they have been used for breeding. The closed technique is also recommended for colts that have had a scrotal hernia.

Complications and risk

Castration is a routine procedure, however, as with any surgery, it is not without risk. In the vast majority of cases castration is straightforward and uncomplicated, but around 1 in 5 cases may develop complications.

There is an element of risk with general anaesthesia of any healthy horse, however every attempt is made to minimise the risk, and the vast majority of our castrations are done standing with sedation and without any complications.

Bleeding from the surgical site is common post-operatively and a small amount of blood dripping for the first 24 hours is normal. If more than a fast drip, or a constant stream of blood lasts for over 2 minutes, veterinary attention should be urgently sought.

Post-operative infection of the surgical site is the second most common complication. Swelling becomes apparent and the colt may appear lame behind due to the swelling, or be depressed and inappetant. Rarely, infection can develop in the abdomen and the horse may additionally appear unwilling to move and very unwell. Veterinary attention should be sort.

If anything is seen hanging down from the surgical incision, veterinary attention should be sought. Usually, this is just a small piece of the vaginal tunic (fibrous sac that the testicle would have been surrounded by), which can be trimmed off by the vet.

Very rarely, a serious complication can occur when intestines prolapse through the castration site. This is an emergency that requires immediate veterinary attention.


Occasionally, one or both testicle/s may not descend into the scrotum. The retained testicle/s can be lying anywhere from the inguinal ring (groin) to near the kidneys in the abdomen, and often they are very small.

If one or both testicles have not descended by one year of age, it becomes increasingly unlikely that they will do so, although occasionally inguinally retained testicles can drop up to the age of 4.

Retained testicles will still produce testosterone so masculine and aggressive behaviour can be expected, and some rigs are still fertile. For these reasons, and because retained testicles may be prone to developing cancer, it is advisable to refer rigs for surgical removal of the testicles in a hospital facility.

Sometimes older horses with an unknown history are presented to us as possible rigs because of masculine behaviour. To determine if the animal is a gelding or a rig, examination, ultrasonography and endocrinology (blood tests) can be used.

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