April 2019 - Miniature Horses
Join AAEP this month as our expert, Dr. Barbara Kahl, answers all of your health questions concerning the miniature horse.
Click here to read this month's questions and answers.
I would like to know if the horse will really get bigger/muscular if he is castrated at an older age?(View Answer)
Thank you for the question. We see two aspects to your question here, the first being if the stallion gelded later would grow taller (bigger), and the second being if he would become more muscular.
To answer the first part of the question, we have seen research in multiple other species such as dogs, cats, cattle, and goats that castrating earlier actually enables them to grow taller. The theory behind this is that every animal has growth plates in each long bone in their body that close within a specific time window as the animal matures. When the growth plate closes, the animal’s growth in that long bone is completed. One factor influencing the timing of these closures is the presence of androgens, or sex hormones. In the other species, we have seen that early castration delays the closure of these growth plates, which causes the animals to grow taller than their intact counterparts.
The second part of your question is perhaps more difficult. We know that stallions that are allowed to remain stallions throughout their puberty age (12-18 months) do develop secondary sex characteristics such as a cresty neck. We see many muscular stallions in disciplines such as halter, Thoroughbred racing, and others. However, we have not found any research documenting that stallions are indeed more muscular than their gelding counterparts. In many disciplines, colts are left intact until management or performance is affected by undesired behaviors, but these horses are also generally wanted as breeding prospects if they are outstanding athletes. Further research is warranted on this topic. Jennifer Reda, DVM, Steele Equine Veterinary Services, Zolfo Springs, FL and Stephanie Regan, DVM
What are the negatives to castration other than not being able to reproduce?(View Answer)
Thank you for this great question. Many owners consider castration a routine procedure and expect that nothing could go wrong. In fact there are many complications that can occur, and the less severe of which are not infrequent. It is important to remember that whether it is performed in the field or in the hospital, whether standing and sedated or lying down under general anesthesia, castration is still surgery. As with any surgery, there is an inherent risk of complications, even when performed by experienced surgeons using proper techniques. It is estimated that about 10% of horses undergoing routine elective castration will experience complications related to the surgery, most of which are mild and can be resolved in the field with no long term effects.
Some complications that may occur after castration would be swelling or edema of the scrotum and surrounding tissues, bleeding, infection, or herniation of tissues or possibly even intestines through the castration sites. Some of these can be treated in the field—i.e. a swollen castration site can be manually reopened and then cold hosed and treated with anti-inflammatories, or bleeding from the spermatic cord may be able to be fixed by ligating the bleeding vessel in the field. Some complications may require referral of the patient to a hospital—such as if the bleeding cannot be stopped, or if the horse develops an infection of the spermatic cord develops that requires surgery to remove. A rare but serious complication is called eventration, where the intestine actually prolapses through the holes made to remove the testicles, and this would require immediate surgical referral. Certain breeds are more predisposed than others to this. Standardbreds and draft horses are good candidates for primary closure castrations at a referral setting for this reason. Any open castration, especially performed in the field, also has the chance of an ascending infection of the abdominal cavity, called peritonitis. This is also a serious, life threatening complication which may require hospitalization.
Other than surgical complications, there are no medical long-term negatives of being a gelding of which we are aware. Geldings live equally as long as stallions if not longer, they are fully athletic and capable of performing in every discipline, and they do not have some of the risks that stallions face for genital-related problems such as testicular cancers, scrotal hernias, and testicular torsions.
Don’t let these complications dissuade you from castration! Castration can be a useful, vital procedure that creates healthy and happy geldings that will be serviceable to their owners for many years, if breeding is not a necessity. However, as your question so astutely points out, it is important to realize that there can be complications associated with castration, as there are with any surgical procedure. Below are some links to articles that may shed more light for you on the issue of castration complications and the statistics regarding their occurrence.
“How I Manage Castration Complications in the Field” by Dr. P.O. Eric Mueller, presented at the AAEP National Convention in 2015.
Incidence, management, and outcome of complications of castration in equids: 324 cases (1998–2008) -http://avmajournals.avma.org/doi/abs/10.2460/javma.242.6.820?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed
Jennifer Reda, DVM, Steele Equine Veterinary Services, Zolfo Springs, FL and Stephanie Regan, DVM
I have always gelded my colts at about 5 months of age, before they are weaned, so the mare is with them for comfort and to keep them moving. Is there any science to indicate that this early castration might be detrimental to their long-term health or performance prospects?(View Answer)
Great question! Many veterinarians and horse owners castrate at around the time you described, 5-6 months, as long as the testicles are fully developed and fully descended. At this age, the testicles are smaller and easier to remove, and there is also less of a risk of severe bleeding post-operatively. Most weanlings we have done recover very quickly and don’t miss a beat going back to their normal lives.
Thus far, we have not found any scientific evidence or peer-reviewed research paper that castration as a weanling has any negative effects on the horse’s long-term health. In fact, there are large retrospective studies that do not correlate age with increased risk of complications. Stallions can develop some undesirable medical conditions that geldings do not, such as testicular torsion or scrotal hernias. In terms of performance, some of this depends on discipline. Disciplines such as halter horses often desire more heavily built, muscular horses. This horse is not able to “perform” any better in terms of any athletic capacity, but simply the breed standards on which they are judged may favor the musculature of stallions. Geldings are often high achievers in both the English and Western performance horse worlds, preferred for many hunter and jumper disciplines. We do know scientifically that geldings grow taller than stallions—the growth plates in their legs remain open longer when they are castrated early, thus allowing them to grow taller. Certainly, many people like to keep their horses intact for potential breeding purposes if they show aptitude in their sport.
Many owners wait until the colt becomes a management problem to geld them, which is often between 2 and 3 years old. These horses will likely retain some of their stud horse behavior even after gelding, especially if they have been allowed to breed or even mount other mares. In conclusion, your castration protocol is perfectly fine. Jennifer Reda, DVM, Steele Equine Veterinary Services, Zolfo Springs, FL and Stephanie Regan, DVM
What is the most common method for castration? What is the youngest age you would recommend castrating? My colt is 6-months-old. I just brought him home so wanted to give him a chance to adjust to his new life before castration. Is it ok to castrate in the cold winter if your horse is turned out all day?(View Answer)
There are several different methods for routine castrations where both testicles are descended. We would say that in the field most practitioners perform castrations under field anesthesia, using intravenous drugs that will lay the patient down for approximately 20 minutes. The other option would be to do standing castrations, which are performed by many veterinarians at racetracks and training centers, although for a weanling this is not the preferred option. For a standing castration, the horse is sedated heavily but remains standing, and the testicles are removed while the horse is standing. Yet another option is for horses to be sent to a referral clinic where the castration can be performed with primary closure, meaning the incision is closed with suture and the scrotum is not left open. Any of these methods can be effective and this depends on the veterinarian’s preference, breed of horse, presence of complicating factors, training schedule, etc.
Most veterinarians will castrate using emasculators. The scrotum is opened and the testicles are extracted, and then the spermatic cord is clamped and then cut for each testicle. There is an alternate instrument for castrations called the Henderson which attaches to a power drill, however in our combined experience not many veterinarians are using this instrument. If in the hospital setting, the surgeons may use an instrument called a LigaSure, which is a vessel sealing device that uses energy and pressure to seal vessels up to 7mm in diameter and has been showed to reduce intraoperative blood loss compared to suture ligations.
In terms of age of castration, the timing is usually a product of managerial convenience; i.e. when masculine behavior is intolerable to the owners or it is determined that breeding is not desired in the future. We typically recommend between 6 and 12 months old. That would mean your colt could be castrated at any time now, as long as he has both testicles descended and fully developed. Allowing your colt to adjust to his new home would be fine as you are still well within the 6-12 month window, and it is certainly possible to castrate later in life as well. In regards to the winter, yes your horse can absolutely be castrated in the winter, as long as your personal veterinarian is game. In fact, many practitioners prefer winter over summer, as they don’t have to deal with the humidity and the insects. If you had any concern as to weather or turnout conditions, primary closure is also an option as there would be no open incision. However, this would need to be performed at a referral facility. And finally, turnout is ideal for horses that have just been castrated in the field. In fact, the more walking around and even actual exercise post-castration such as lunging, the better because it reduces swelling and inflammation. If primary closure is performed, horses are usually stall rested and hand walked for two weeks until the incision is healed, and then can return to full exercise. Jennifer Reda, DVM, Steele Equine Veterinary Services, Zolfo Springs, FL and Stephanie Regan, DVM
Can you castrate a 12-month-old colt if the testes have not dropped yet? What is the best age to castrate for maximum physical development?(View Answer)
The condition you are describing in your colt where one or both testes fail to descend into the scrotum is called cryptorchidism. Other terms for this are that the colt is a “crypt” or a “rig” or a “ridgeling”. While the colt is still in utero, the testicles should descend through the abdominal cavity and inguinal canals into the scrotum. This usually occurs in the last 30 days of gestation or first 10 days after birth. If your colt still has both testicles undescended at 12 months, there is only a small chance that they will descend at all. So where are the testicles? They could still be all the way up in the abdomen, or they could be located in the inguinal region. If in the inguinal region, they are often palpable. If the testicle is in the abdominal region, it will not be palpable but may possibly be visualized on ultrasound.
Moving on to your next question of if your colt can be castrated, the answer is yes. However, since his testicles are not descended, this will be a specialized castration performed by an experienced veterinarian. The best way to castrate a bilateral cryptorchid stallion is through laparoscopic surgery. This is done under general anesthesia. The colt is placed on his back, and a small incision is made, through which the device called the laparoscope is inserted. The laparoscope contains a camera where the testicle can actually be visualized and then removed. This surgery is minimally invasive, meaning the incisions used for this are small and the surgery is very precise. If for some chance there is any problem with visualization of the testicle via the laparoscope or there are complications, the horse is already in an appropriate, sterile surgical setting with proper anesthetic equipment and monitoring to convert the surgery into an open approach into the abdomen.
Alternatively, skilled field veterinarians will also attempt to do cryptorchid surgeries in the field. This is possible for inguinal testicles, but usually for testicles in the abdomen practitioners prefer to do these surgeries in a sterile environment. Sometimes it can be hard to determine where the testicle is until the horse is already anesthetized, and you run the risk of not being able to finish the surgery if the testicle is retracted into the abdomen or just simply isn’t where it was thought to be originally. Even inguinal testicles (high flankers) should be castrated with an assistant to run and monitor anesthesia as these can be longer, more tedious procedures than a simple castration. Also, multiple attempts at removing a cryptorchid testicle can make surgery in the future at a referral clinic more difficult due to scar tissue, and often the history is lost along the way of whether the testicle was actually removed or not.
To answer your last question about the best age to castrate for physical development, the most common time we like to castrate is between 6 and 12 months old. That being said, we have castrated very young and very old stallions. However, there are some reasons behind the 6-12 month old recommendation. First, the testicles have adequate testicular development after about 3 months old, which makes them easier to find and sever. Second, the chances of excessive bleeding are reduced when you geld at a younger age as the testicles are not quite as large as waiting until, say, 3 years old. Younger horses often tolerate anesthesia better, recover more quickly, and heal faster than older horses. The size of the opening to the abdomen that the spermatic cord travels through can differ with maturity, meaning the risk of abdominal content coming through that opening can be higher with an open approach in the field. Finally, stallions that are castrated later in life tend to retain more of their learned stallion behaviors even after they have been gelded. For all of these above reasons, we would recommend castrating your colt now, ideally laparoscopically. Best of luck to you and your soon-to-be gelding! Jennifer Reda, DVM, Steele Equine Veterinary Services, Zolfo Springs, FL and Stephanie Regan, DVM