Castration is one of the most common routine surgical procedures performed on horses in the UK. To facilitate management and to avoid unwanted breeding most male horses are castrated. Only a small proportion is kept ‘entire’ (uncastrated) for breeding purposes.  Horses are most frequently castrated at home under field conditions. We have the option of performing the surgery while the horse is standing or under general anaesthesia. More complex surgeries tend to involve a trip to the hospital.  

Horses can be castrated at any age, but a number of factors will influence the timing and the choice of surgical procedure. 

Age 

 Generally, most vets in the UK recommend castrating a horse between the ages of six and 18 months. There are several reasons for this. 

Ease and safety of surgery

In horses younger than 6 months the testicles are generally smaller, which require smaller incisions that heal more quickly. But, if the testicles are very small and immature they may be more difficult to remove in a standing horse. In which case surgery under general anaesthetic may be preferable. Some breeders prefer youngsters to be castrated before weaning. Although there is no evidence to suggest that this is of any benefit or detriment to the horse’s development. It is, however, quite an invasive procedure to carry out at such a young age.  

As the horse grows and develops, its testicles increase in size, with a greater blood supply and thicker surrounding fibrous tissue. In horses over the age of four years (physically fully adult) many vets will recommend performing what is known as a closed castration, where the blood vessels are tied shut with suture material instead of the simpler method of crushing alone because the larger blood vessels and tissue make surgery more difficult with greater risk of complications such as bleeding. This procedure takes a longer time and carries a greater risk of post-operative infection. It is commonly performed with the horse under general anaesthetic. The vet may prefer to carry this out in an operating theatre where conditions are sterile to reduce the risk of complications.

 There is no hard and fast rule as to the precise age at which horses should undergo a closed castration, which will depend on your vet’s preference following examination of your horse to determine the most appropriate technique, depending on its size.  

Development of adult behaviour

Stallion-like behaviour is learnt and develops over time from the onset of puberty. So although some horses will show a reduction in sexual and aggressive behaviour following castration, this is not a certainty. Some horses will continue to act like stallions. Aggression towards other horses is the trait least likely to resolve with castration. So to reduce the risk of these unwanted behaviours, it is best to aim to castrate the horse before these traits develop; usually around the age of three to four years.  

Given these facts, six to 18 months seems to be the ideal age where the horse is mature enough to cope with the surgery, but not too old to increase the risk of complications. 

Number of testes 

In order to carry out a castration safely and effectively under field conditions, both testicles should be present in the scrotal sac. Your horse may allow you to check this. But sometimes a vet may be needed to sedate him to facilitate examination; particularly if the horse is not used to handling or if the testicles are very small in size or difficult to palpate.

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Testicles usually descend between thirty days before and ten days after birth and are usually present when the foal is born. To reach the scrotum they must pass through a small opening in the body wall. Testicles tend to grow slowly in the first ten months of life and as they may descend through this opening more easily when small, it is often advisable to adopt a wait and see approach if the testicles have not descended before a year of age and are therefore not palpable in the scrotum. 

As the testicles tend to grow more rapidly during later puberty (after about 18 months of age), it becomes more difficult for them to descend through the narrow inguinal ring after this age as their size increases. Although not impossible, it is unlikely that testicles that have yet to descend at 18 months will do so. As such, more complex surgery will be needed to remove them. Most castrations of cryptorchid horses (those with one or fewer descended testicles) are carried out in a veterinary hospital. This is because vets may need to perform abdominal surgery to locate and remove the undescended testicle. Veterinary surgeons in the UK will not remove a single descended testicle without removing the retained testicle first as they need to be sure that both testicles are removed.   

Season of the year 

In the UK, most veterinary surgeons prefer to carry out castrations during the spring or autumn when the months are cooler; to avoid the summer when flies are more prevalent. Flies are attracted to the open wounds. They not only increase the risk of infection but are also a great source of irritation. 

Additionally, it is also best to avoid the very poor weather conditions of winter. We like to get horses out and walking in the post-operative period; something that isn’t always possible in frosty weather or advisable in very muddy conditions when mud splashed from puddles may contaminate the wound.  

Vaccination status 

Tetanus is a profoundly serious and potentially life-threatening disease occasionally seen in horses. It is caused by a toxin released by a bacterium that lives in the soil and digestive tract and tends to thrive in deep wounds such as those associated with castration. If a horse develops tetanus, it can be extremely difficult and costly to treat. So we try to prevent the disease instead. 

The main method of prevention is vaccination. As the body needs time to develop immunity, we recommend vaccinating your horse with two vaccines four to six weeks apart prior to castration. If this is not possible, at least one vaccine four weeks prior to castration. And a vaccine at the time of castration will provide some protection. In certain cases when unavoidable, such as with unhandled horses, vets will give the first vaccine at the time of the surgery sometimes accompanied by a short acting antitoxin. But this is a less effective way of protecting against a potentially fatal disease.  

Other considerations 

Presence of mares 

Veterinary surgeons usually recommend keeping your newly gelded horse away from mares for four to six weeks. This is to avoid any undue excitement during the healing period. It is worth remembering that geldings can remain fertile during the first few weeks post-operatively as some viable sperm will remain in the genital tract. It is best to schedule surgery when you can guarantee your facilities will allow you to separate your horse from his lady friends following the castration. 

Training and handling 

It is hugely helpful if you have the time to train your colt to a headcollar and to tolerate basic handling prior to the day of surgery. It will make the procedure less stressful for all concerned. And will reduce the quantities of drugs needed to carry out the castration safely. It will also make examining and checking on your horse, or administration of drugs if needed, easier in the post-operative period.  

Although castration is a very common procedure, complications, such as bleeding or infection, can occur. It is important to make sure that you have the time to check on your horse frequently following surgery. This is so if complications arise, they can be identified and treated sooner rather than later.  

Summary 

In an ideal world colts would be well handled, healthy, fully vaccinated against tetanus with two testicles present in the scrotum at the time of surgery. However, no two cases are the same. We often must adapt our approach based on any number of factors, including those outlined above. Always talk to your vet about your individual situation. They will be able to tailor a plan to suit both you and your horse to ensure the best possible outcome for your circumstances.  

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