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Castration of Horses

Castration is the most common surgical procedure in horses with almost every male horse going through the procedure. Done properly the incidence of serious complications is very low. In spite of that, many of todays horses owners have not gone through the procedure and have anxiety about it. A common problem encountered with castration is cryptorchidism. This article explains timing, what to expect, how the procedure is done, and post-operative care including recognition and care of complications. Also covered is the diagnosis and method of dealing with a cryptorchid stallion.

Stallion behavior and the first two years

Around 12 to 16 months of age a colts testis begin to secrete testosterone. Now he will not become fertile until around his second year, perhaps a little earlier, but he will begin to display stallion like behavior. You can typify this behavior as: easily distracted, particularly by other horses, increased attempts to communicate with other horses, increase in colt like play behavior that may shape itself into aggressive acts like nipping, head butting, pawing and kicking.
The behavorial problems are dependent on both the quality of the training and innate personality of the horse. There are some stallions that with a minimum of training are really nice guys and then their are stallions with good, consistent training that are dangerous to handle. The majority fall in between with consistent, experienced training and handling they are safe and enjoyable horses to be around. You just have to remember about most stallions: everyday is a training day.

Gelding Behavior

It is this tendency to aggression and easy distraction that make geldings better riding horses. Being gelded is not a cure for all behavorial problems. Many bad behaviors are not related to testosterone levels but lack of training or past bad experiences. By gelding a horse you make training easier but not unnecessary. Another consideration is not all geldings respond to castration in the same way.
All the testosterone is never out of a geldings system. The adrenal glands are a source of testosterone and testosterone-like hormones, but geldings have a lower level. It appears that the behavorial centers of a horse's brain differ in sensitivity to testosterone from horse to horse. Some horses are still stimulated by the background level of testosterone despite a complete castration. A study that looked at a very large number of castrations over several years found that following castration: 70% become perfect gentleman, 25% retain a few stallion characteristics but do not mount and enter the mare, and 5% showed no difference in behavior before and after castration. The horses that retained stallion like characteristics were checked to be sure the surgery correctly and no problem was found. It was surprising to find that the age at castration and sexual experience had no bearing on the behavioral outcome. Those castrated well before maturity went on to mature with the same behavorial spread as those experienced stallions castrated later in life.

Following castration of the mature horse the decrease in stallion like behavior is almost immediate but is not complete for 4 to 8 weeks. The sperm, stored in the epididymis which is usually attached to the testicle, is removed from the horse at castration. Horses should be sterile following castration but one always worries about those few sperm left in the ductus deferens (the tube the sperm travel in to get to the penis). Occasionally the epididymis is not attached to the testicle and may be left in during a closed castration. These horses may remain fertile for an unknown period. Horses with the epididymis left in are referred to as "proud cut". This use to be done on purpose to promote showy behavior however research has shown that the testosterone levels in these horses is no greater than horses with complete castrations.

What is the best time and age to geld?

Horses may be gelded at any time of the year. Traditionally cold weather has been preferred because the fly's will not bother the horse and there is a subjective feeling they have fewer complications. However with good technique and a little extra post operative care horses can be gelded at any time of the year. Avoid rainy or very hot weather as both tend to reduce the amount of movement by the horses.
The age to geld depends on your objectives. Horses should not be gelded prior to four months of age. The inguinal canals are larger on suckling foals and the serious complication of intestinal herniation and eventration through the castration incision are much greater. If the only objective is to create a good riding horse castration should be done as early as possible. The first cold month after 4 months of age is a good time. There may be a reason to wait. If the secondary sexual characteristics are desirable: heavier muscle and bone and a thicker body you may want to wait until the horse has developed to the desired body condition. Some of this remains following castration. What early castration does to the eventual height of the horse appears to still be a debated subject. Different research projects have suggested stallions may be shorter, the same, or taller than if they were gelded.

There really is no great increase of risk with a older stallion. The blood vessels are larger so the clamping needs to be thorough. The cords could be ligated before cutting though I do not feel this is necessary. The increase size of the horse makes laying the horse down and getting him up harder, so be sure there are two experienced hands available. One can manage the rope attached to the halter while the other the tail. This will ease the let down and the getting up.


It is important to have the stallion used to being handled and halter trained. He should not be fed or watered the morning of surgery. He should be checked to be sure both testicles are down prior to anesthesia. A clean dry reasonable soft space needs to available for laying the horse down. A towel to lay the head on and cover the eyes is a nice thing to have.

Castration Techniques

There are so many ways to castrate a horse we cannot cover them all here. The technique that the surgeon is most familiar with is probably the best one to use. The most important surgical factor to reduce complications in an open castration is the use of a wide incision to allow for plenty of drainage and avoiding premature closure of the surgery site. Horses can be castrated standing or laid out. The degree of anaesthesia can range from none at all to completely unconscious. The incisions used vary greatly also. Traditional is two slits, one for each testicle. There is a growing trend to make a larger incision removing a portion of the ventral scrotum and much of the median raphae. This allows for better drainage and help tighten up the tissues around the scrotum so that there is less of that annoying squooink noise some males make when ridden.
There are still important differences in technique. Each testicle sits in an inner bag inside the scrotum. This inner bag is called the vaginal tunic. Some expose the bag and castrate through the bag without opening it up, called a closed technique . Others slit the bag open, cut the muscle and ligament that attach to the testicle and trim away the excess tunic and cork. This prevents the horse from pulling back the testicle as the vascular bundle is clamped and ligated. Using this open technique I have never had excessive hemorrhage as a complication.

There has been a growing interest to sewing up castrations following field surgery. Some using the technique are very satisfied while others have had complications with excessive swelling, infection and sclerotic cords.

The clamping is important to prevent excessive hemorrhage, though there always is some bleeding. Generally 5 minutes of a strong clamp per cord of vessels will prevent even the largest set of vessels from excessively bleeding. It is always good to remember that horses generally have 6% of their body weight as blood and can loose as much as 15% acutely without serious complications. For a 600 lb colt that comes to over 2 quarts of blood or enough to paint the wall of a good size room. Dripping blood following castration is expected and will slow and stop over the next hour or so.

Though serious hemorrhage is a rare complication many first time observers of a castration worry about the blood. If you see your horse all of a sudden begin bleeding heavily stop and watch for a few seconds. Horses will stand in ways that dam up the blood and, when they move, they release the dam causing a short term heavy bleeding. If this is what has happened it will stop in a few seconds. If there is a persistent stream of blood for more than 5 or 10 seconds call the vet. While waiting, keeping the colt calm is of paramount importance. With excitement the blood pressure will rise and make the bleeding worse. If the colt will allow it stuffing the incision with a small thin towel and keeping pressure on the towel may slow the bleeding, certainly pressure can be applied to the source of the bleeding once the colt loses consciousness. Acepromazine can be a two edged sword: it will lower the blood pressure to slow the bleeding but if the blood loss is significant may cause fainting.

Post Operative Care

The most important care is a lot of pasture exercise to promote good drainage. Avoid keeping him up for all but short periods of time. The horse will usually run a low grade fever the first week or two. The horse should continue to eat and act fairly normal. If he gets out in the pasture and mopes around try phenylbutazone and lunging twice daily. During fly season I will apply antiflysubstance (see your vet) lightly to the incision site about every 2 or 3 days depending on how many flies I see.
With an open castration I do not use systemic antibiotics. Open wounds will become infected no matter what antibiotic is chosen. But the antibiotic will influence what organisms will predominate. As long as the surgery site drains well, the infection does not internalize and ascend the tissues: it drains as the surgery site heals itself from the inside out. If drainage is impeded antibiotics do not prevent infection but may select for more difficult to treat organisms.

There almost always is some post operative swelling for the first week. It collects down in the end of the prepuce, where the penis comes out. It may get to the size of a soft ball and that's OK. If maintaining drainage is difficult, usually do restricted exercise, I recommend bute or furosemide to control swelling and aggressive hosing of the surgery site once or twice daily. The first sign of impeded drainage will usually be a stiff gait closely followed by increase swelling around the incision. First the horse should be manually examined to see if there are any clots or adhesions forming prematurely to prevent proper drainage, these should be removed. This may require sedation and a twitch. Then daily the outside of the incision should first be hosed off to remove all the exudate, then the hose, under the pressure you can generate with a nozzle at just about full force, should be directed up into the incision site thoroughly flushing it out. Generally the stiffness and swelling will resolve in 24 to 48 hours.

Other Complications of Castration

We have discussed eventration, excessive hemorrhage, and poor drainage and its principle clinical sign: post operative swelling. Herniation of a segment of bowel through the inguinal canal and eventration through the incision can occur in adults also. Some report the incidence may be as high as 1 in 300 surgeries. This usually occurs when the horse stands, so this is an important time to check the incision. Look closely at the testicles, bowel will be of grey-pink color and this will help keep you from confusing it with fat which is yellow and large clots which are deep purple in color. The prognosis for this complication is poor and it is an immediate emergency. Until the vet gets there all you can do is keep the colt quiet and still.
A infrequent but completely preventable problem is facial nerve paralysis from laying on small rock or halter ring. Have a soft towel to lay the head on and be sure the halter ring is not digging into the bony ridge that runs along each side of the face. No matter how carefully you go over this list I find first time castrators are going to call three times and talk about some of the normal healing processes particularly hanging blood clots and post op erative swelling. The single most consistent indication something is wrong is the colt going off feed and excessive stiffness.


When a testicle is retained in the body the term is cryptorchid. Horses can either have one or both testicles retained. Though most stallions have their testicles down when they are born, occasionlly they do not descend until a year of age. There have been reports of this happening even later, though this is uncommon.
The testicles can be in either the inguinal canal or the abdomen. Rectal palpation may be able to diagnose a abdominal cryptorchid. The location is important as those in the inguinal canal can be removed during a routine castration. If the testicle is abdominal it must be removed through an abdominal incision.

Occassionally a horse is bought with an uncertain castration history that will display stallion like behaviors. As outlined above this may be normal for some horses but when uncertainty exists blood tests can settle the question in adult horses. There are two blood tests: testosterone levels and estrone sulfate levels. Testosterone levels below 25 pg/ml are consistant with geldings and over 100 pg/ml with stallions. Unfortunately there is a percentage of horses that will fall in between these two numbers whose status will be uncertain. To test those that fall in between you can take a blood sample and then give 6000 IU human chorionic gonadotrophin (HCG) IV to the horse. A second blood sample is taken at least between 1 and 24 hours later. The HCG stimulates the testicular tissue to release testosterone and if it is present it will cause a minimum of a 4 fold rise in the second sample. Accuracy of this technique is about 95%.

A single estrone sulfate level is also about 95% accurate. There are some limitations to this test. It should only be used on horses well over 3 years old and is not accurate in donkeys. In both cases a positive for testicular tissue is accurate but false negatives are common. The labortory should have established normal values for stallion.

A technique for dealing with cryptorchids where the location of the testicle is uncertain has been to first attempt a normal castration and go look for the missing testicle first. If found, the testicles can be removed. If not I go ahead and remove the down testicle than allow the horse at least a month to recover then remove the second testicle through a flank incision. It is best not to do the two surgeries together as the regular castration requires exercise but the flank incisian should be rested for a week.
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