Castration is a common surgical procedure performed on intact male horses to prevent unwanted breeding and improve behavior in geldings by removing testosterone which can lead to stallion like behaviors, aggression, inattention during work and other unwanted behaviors.
Castration can be performed as early as 6-8 months of age as long as both testicles are descended into the scrotum. Often castrations are performed around 1-2 years of age. Occasionally 1, or rarely both, testicle can remain up in the inguinal canal or the abdomen. This is called cryptorchid. In young stallions, we can give them more time and sometimes as they age and the testicles become larger they will descend and a routine castration can be performed. If the testicle/testicles fail to descend into the scrotum, the horse will have to be referred to a surgical facility for a more intricate surgery to find the undescended testicle.
Depending on the size and temperament of your horse, the castration may be performed standing under heavy sedation or under general anesthesia in a clean, level place outside. If possible, it is best to perform castrations during cooler weather to decrease risk of infection from heavy fly activity. In horses, due to their large blood supply and significant drainage post operatively, we do not close the incision with sutures as they do in dogs; rather, the incisions are left open to drain and heal in over approximately 2-3 weeks. Because of the significant drainage, diligent post operative care by the client is vital to limit complications and speed recovery.
What to expect:
Your horse will need to be current on vaccines, having at least the first set of Eastern, Western encephalitis and tetanus 3 weeks prior to castration.
A thorough physical exam will be performed to ensure the horse is healthy to undergo surgery
A thorough history will be obtained to ensure there has been no recent illness that could delay healing or put your horse at increased risk under anesthesia.
The castration will be performed on the farm by a qualified veterinary team and post operative antibiotics and pain medication will be prescribed and thorough post operative instructions will be communicated.

Possible complications to be aware of:
Though performed routinely, equine castrations can come with complications.
Hemorrhage: Due to their large size and significant blood supply to the testicles, in the immediate post operative period (first 24 hrs) horses are at risk of hemorrhage from the testicular cord where the testicle was removed. The older the horse is, the more at risk of hemorrhage they are due to increased testicle size and size of the blood vessels supplying the testicles. To limit hemorrhage, keeping the horses contained in a stall or similar small space and keeping them as calm as possible is vital for the first 24 hrs. donkeys are at increased risk of hemorrhage compared to horses, thus the earlier the better for donkey castrations.
Swelling: some swelling after castration is normal, it will frequently be the worst for the first 48-72 hrs, then should start to decrease. Daily exercise and cold hosing help limit swelling.
Infections: the procedure is performed as cleanly as possible and post operative antibiotics are prescribed to decrease risk of infection, however post operative care and exercise is vital to limiting infection. Due to the significant amount of drainage from the surgical site as the incisions are healing, if the incision starts to seal closed too quickly, the serum drainage will be trapped and can become infected causing pain and significant swelling. Following a daily exercise program prescribed by your veterinarian is vital to preventing premature incision closure and infection. They are most at risk of this happening in the second to third weeks post operatively.
Herniation: a rare and dangerous complication associated with castration is herniation of bowel through the incision site. Frequent monitoring during the first 24 hrs post operative to catch this early if it were to happen is key to successful outcome. Tennessee walkers are at increased risk of this complication due to large inguinal openings. In young animals we can perform a closed castration in with the entire vaginal tunic (thick tissue over the testicles) is cut and ligated in 1 which limits this complication. In older animals, we have to open the tunic to ligate the blood vessels separately to limit risk of hemorrhage possibly increasing risk of herniation.