If you ask the average horseperson what a tranquilizer is they will likely tell you it is a drug that calms, sedates or quiets a horse. No distinction is drawn between a tranquilizer, sedative, hypnotic or any other class of drug affecting the horse’s brain.
Even among pharmacologists and veterinarians, there is a gray line between all the centrally acting drugs, and even antidepressants sometimes get lumped in with the tranquilizing drugs. However, the distinction between drugs is more than just an academic question. Different drugs have different actions on the brain, and while you may think you’re getting the same result, the changes in the horse may be deceiving.
The most widely used tranquilizer in horses is acepromazine or “ace,” a member of the phenothiazine group of tranquilizers. In human medicine, these drugs are reserved for the most severe cases of psychosis and are responsible for the zombie-like, blank-staring state portrayed in movies about mental hospitals. Ace does not make a horse happy, peaceful or calm — it makes him dull and flat.
An important characteristic of ace is its effect on learning. With both people and experimental animals, the learning of new tasks is greatly blocked by ace. If you use it to make a horse more manageable during schooling you are wasting your time — he won’t remember most of what you try to teach him.
Ace also has a direct effect on the muscular system, causing relaxation. It decreases spontaneous motor activity, which means horses that fidget, pace or paw are likely to stop this behavior even at relatively low doses. The lack of coordination and stumbling that occur with ace are a result of a combination of effects on the brain and the muscular relaxation.
Ace Side Effects
Acepromazine has potent side effects. We all know ace will cause the penis to drop. Although rare, ace can result in a permanent paralysis of the muscles that retract the penis. There is no particular dose more likely to do this and no way to predict what horse may be affected.
Heart and circulation are affected by ace, which always causes a drop in blood pressure. In the initial stages after administration, irregular heart beat and blocked conduction of impulses through the heart are common. These effects make the use of ace in electrolyte-depleted, exhausted, injured, colicked, or otherwise stressed/shock horses potentially dangerous.
Ace also affects the blood. Even low doses cause a drop in red-blood-cell counts, hemoglobin and hematocrit. The effect increases with dosage so that at full dose (0.1 mg/kg or about 50 to 55 mg for average adult horse), there is as much as a 20% drop in red-cell parameters.
Ace also interacts with medications used to achieve general anesthesia. If you used ace to facilitate emergency treatment of an injury or colic, and the horse is found to require surgery, it is imperative that the anesthesiologist be informed.
Few users realize ace accumulates in the body. Ace is distributed widely throughout the tissues. While blood levels drop off quickly, a slower elimination phase follows before all the drug is cleared. If a horse is given ace daily, he will eventually need smaller doses for the same effect. Horses receiving ace regularly may test positive at competitions for as long as three weeks after the drug has been stopped.
Most people think ace makes a horse safer to work on, safer to ride, less likely to “flip out” in a trailer, etc. This is not necessarily true. Ace is useful in abolishing conditioned/learned responses, but it will not abolish self-defense mechanisms. For example, if a horse had a bad experience loading or an irrational fear of the sound of clippers, ace will help suppress his usual responses to those circumstances. However, he will still react to pain, loud noises or even an unexpected touch — often with surprising speed and strength. And there are more misconceptions:
Myth: Getting ace on your own skin can cause problems.
Reality: There are no special safety precautions when using ace, and no special toxicity to people compared to animals. Overexposure may cause eye or skin irritation. If you get it on your skin, flush with water. If you get it in your eye, flush with water and call your doctor. Do not ingest it.
Myth: Adrenaline can overide the effects of ace. If your horse is already upset about clipping giving him ace won’t do any good.
Reality: Giving ace after the horse is agitated may mean you need a slightly higher dose to get the same effect, but it will work. As with the initial dose, you must allow adequate time for the drug to take effect. The horse should be left undisturbed for this time period. When you come back, the horse will be calmer.
Adrenalin is metabolized in a matter of seconds to minutes and will not affect the response to ace, even if you give it after the horse is worked up. Regardless of the dose used or whether or not the horse was agitated to begin with, a sufficiently strong stimulus can still cause the horse to react. A combination of common sense, working quietly and using low/moderate doses of acepromazine to “take the edge off” will get the job done just as well as high doses and will avoid dangerous incoordination.
Xylazine (Rompun/TranquiVet) is another common tranquilizer. Properly classified as a sedative and muscle relaxant — both effects occurring through interference with activity in the brain — xylazine also has some analgesic effects, but these last only for 15 to 30 minutes, tops, and are highly unpredictable. It is generally not safe to do painful procedures under the effects of xyalazine alone, although it may make the injection of a local anesthetic easier.
Like ace, xylazine has side effects. Xylazine slows breathing, an effect described as similar to the breathing depression seen with sleep. Xylazine also has a profound effect on the intestinal tract, causing marked slowing of motility, particularly in the small intestine.
A horse under the effects of xylazine will usually drop its head farther than with acepromazine and is generally less likely to react to procedures being done around the head. This makes the horse appear to be more sedated than he really is. As with ace, any loud noise, pain, sudden movement or unexpected touch can cause the horse to react quickly and violently.
Because of the effects on intestinal motility, problems could be encountered if xylazine is given to a horse that has just completed a large meal. Exactly how much of a problem this could be is still a matter of debate, but it would be wise to avoid xyalzine under those circumstances.
Because of the intestinal-tract effects, mild analgesic effects and lack of significant effects on blood pressure, xylazine is a favorite to use in the treatment of colic. However, some colics can be made worse by this drug. If the horse is experiencing discomfort because a section of intestine is damaged and not propelling intestinal material properly, xylazine could make matters worse.
Right And Wrong Uses
Too many people approach the use of tranquilizers with a casual attitude, thinking it is the equivalent of a person taking a Valium to “mellow out.” These are potent drugs with potentially serious side effects.
The main indication for tranquilizers is for the safe performance of medical procedures that can’t be accomplished by other methods of restraint. In all other cases, the risks and benefits should be carefully weighed. Avoid using tranquilizers for routine tasks, such as braiding or pulling manes. The horse should be trained to stand or, if absolutely necessary, twitched a few times until he learns he must behave.
More often than not, horses that put up excessive resistance to routine procedures have learned they can get away with it. Having the horse handled and restrained by someone who knows how to proper ly deal with the behavior is likely to cure the problem in short order. Tranquilizers will not.
Tranquilizing for trailering is another common abuse. For the handful of horses that go bonkers in a trailer, either because they can’t overcome their fear of being restrained in a small spot or because of a prior bad experience, low-dose tranquilization may be necessary in a pinch.
However, it is nearly always possible to overcome the “anxiety” by devoting time to repeatedly loading and unloading, feeding in the trailer, having the horse stand with the trailer not moving, repeatedly shipping for short distances, etc.
It is also important to identify exactly what it is that upsets the horse. If the sound of engines, horns or other stimuli, such as lights flashing, are causing the problem, tranquilizers won’t help and may make the situation worse as the horse will still react to these things but will be off balance because of the tranquilizer.
Using ear plugs on your horse when shipping is effective with many horses, blocking out or muffling the rattling and banging of the trailer as well as upsetting traffic noises. Yoiu can buy equine ear plugs or you can make some yourself using rolled-up gauze covered by nylon stockings.
The use of tranquilizers, especially acepromazine, during breaking and training of young horses is completely counterproductive. All the fears and behavior patterns are likely to recur as soon as you stop using the drug, unless the horse is worked with for a long-enough period after giving the drug so that he has recovered from the effects (this means hours!) and is responding when not under the influence. If you do not have the expertise to handle a young, unbroken horse turn him over to a professional.
Similarly, there is no place for tranquilizers when hacking, foxhunting, showing or otherwise riding. Even light tranquilization interferes with the horse’s muscular functioning and coordination, greatly increasing the risk of injury for both rider and animal. If you aren’t skilled enough to ride the horse you’re assigned, decline the invitation to go.
We have all seen horses, usually at unrated competitions, that are obviously tranquilized. They go around the ring in a daze, nose almost on the ground. It doesn’t take an expert to spot these horses as tranquilized. The sad thing is that often these horses will get pinned if they can manage to make it over a course of jumps cleanly. It’s tempting for people to take the “easy way out” to make a less-than-perfect horse look bombproof. If your trainer uses tranquilizers to help you show your horse, question why.
A proper use of tranquilizers is when a horse has been stall bound for a prolonged period as a result of an injury and is being brought back. No one can reasonably expect these horses to behave. If they had their way, they would break loose immediately and run until they were too tired to run anymore. Proper tranquilization facilitates initial stages of handwalking and turn-out in small quarters, such as a bull pen. Done properly, the tranquilized state lessens the chance of injury compared to if the horse were simply allowed to carry on.
We realize there are situations, especially with a new horse, where you find out unexpectedly that the horse acts badly for some simple routine task, like clipping. If you don’t have time to properly reschool the horse, low-dose tranquilization may help with the immediate problem but should not be used repeatedly as a substitute for proper training.
Tranquilizers are also appropriate when dealing with an injured horse that is agitated and will not submit to emergency care. However, before reaching for a tranquilizer, allow the horse to calm down, take vital signs (temperature, pulse and respiration) when the horse is quieted and give it one more try. If you still cannot work with the horse, contact the veterinarian with a detailed description of the horse’s current condition and vital signs and follow advice for tranquilization before you give any drugs. Even horses in impending shock may be agitated because of pain and fear. Giving a tranquilizer under those circumstances can have disastrous consequences.
Tranquilizers are controlled drugs, so you must obtain them through your veterinarian, who will instruct you on appropriate dosages for your horse and in what situations. In reality, however, some barns have a bottle of tranquilizer ready to use by whoever “needs it” for their horse.
It’s important to realize the dosage of tranquilizer that appears on a label is the appropriate dose to use for full tranquilizing effect, as in premedicating a horse before surgery. There are almost no around-the-barn situations that would call for this high a dose. Horses vary quite widely in their sensitivity to tranquilizers.
For almost all uses around the barn (except possibly colic), ace is the tranquilizer of choice. It is possible to get behavior modification from this drug at doses that have minimal sedating effects and minimal lack of coordination. Unfortunately, people often use a standard dose, such as “I always give 3 cc to ship,” that is not only too high but also ignores the fact that each horse is different.
As little as 25 mg (0.5 cc of the 50 mg/ml acepromazine) will allow you to clip, braid or load most horses with little difficulty — if you give it time to work. Intravenous dosing is not recommended for non-veterinarians. When given intramuscularly, allow 20 to 30 minutes for the full effect of the drug. If insufficient, you can give increasing 25 mg increments until the desired effect. Be sure to follow the correct skin preparation techniques for the injection.
When using oral preparations of acepromazine (granules), the effective dose will be about five times higher because of differences in absorption. Allow an hour for full effect. An advantage of the oral type is that side effects are greatly decreased to nonexistent.