Tower Equine

Veterinary Surgeons

 

The Big Sleep - October 2013

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Commissioned by Horse & Hound magazine 15 August 2013

Sedatives can be a great help when it comes to accomplishing tasks that horses don't like. Roger Lee MRCVS explains how and when sedative drugs should be used:

The majority of horses are remarkably trusting and obedient, but there are still occasions when they are scared, in pain or just badly behaved. Whether it is for something routine such as clipping or shoeing, or for a potentially painful procedure such as treating a wound, the ability to sedate a horse can be essential both for his safety and ours.

For practical purposes, sedatives can be divided into those administered by a vet, typically as an injection in to the vein, and those an owner can give to a horse themselves. When a vet gives an intravenous injection of sedative, it is usually because a deeper level of sedation is required. This is achieved by using a mixture of two drugs. The first is a true sedative that works by depressing the levels of brain activity. The second is a type of drug called an opioid. Morphine-like drugs are powerful painkillers and they work in conjunction with the sedative to deepen the level of sleepiness. When these two drugs are given into the jugular vein, they take effect in a few minutes. Intially the patient may look a little uncoordinated. Although it is extremely rare for an animal to fall, it is important to ensure that horse and handler are in a safe position.

The full sedative effect is usually achieved within 5 minutes, by which time the horse should be standing with his feet wide apart and his head lowered, oblivious to his surroundings. Sedation lasts for approximately 30 minutes, although this can vary - the more intrusive or stressful the procedure is, the less time the sedation will last (depending on the dose given).

Safety first

This two drug combination is extremely safe and reliable and can be used in older horses and pregnant mares, as well as the sick or injured. The horse needs to be calm, however, when it is injected, otherwise the drugs will have less effect and more will need to be given. Sedative drugs are not cheap - a typical dose for an average horse costs anywhere between £20 to £35. An excited animal with an "adrenalin surge" may need more than double the usual amount, so keeping the horse calm makes financial as well as practical sense.

It is important to remember that while a sedated horse may look sleepy, his reflexes are unaffected and he can still kick or strike out. Both vets and owners have been injured in this way because sedated horses are not able to show the normal body language warning signs that alert us. The opioid part of the two-drug combination is often said to "glue the feet to the floor". Topping this up can stop a horse kicking without increasing the overall level of sedation.

Reducing anxiety

The sedation that owners are most likely to give to a horse themselves is acepromazine, which is usually known as ACP. Usually given by mouth, ACP does not have any painkilling effect, nor is it as strong as other options. This means that it is not suitable for any painful procedures. Its chief use is for calming an anxious horse, for example for clipping or shoeing. Fear or pain can override its sedative effects, however, and increasing the does is often ineffective. ACP lowers the horse's blood pressure so it should not be used in cases of colic, severe injury or shock. ACP does have the advantage of lasting for longer than other substances - up to 6 hours - and because it is available in injection form, vets sometimes add it to a sedative mixture to increase the length of sedation.

A stronger sedative, detomidine, has been available as an oral gel for the past three years. Detomidine is an additional possibility for owners keen to avoid the expense of calling the vet out. The gel is not combined with a morphine-like opioid, however, which means the effects can be more variable.

Tranquil, calm or sedated?

A sedative reduces the level of activity of the brain, making the horse less responsive to its surroundings. A tranquilizer reduces levels of anxiety, without causing sleepiness. There is, however, considerable overlap between the two, and in larger doses most tranquilizers also produce sedation. At very low levels, for example, ACP acts as a tranquilizer and is sometimes given to "take the edge off" a young horse during backing, or to calm a horse doing slow work after injury. At higher doses, however, it does produce sleepiness. For this reason no ridden horse should be jumped or ridden at speed after being given ACP.

"Equine calmers" typically contain a mixture of ingredients including magnesium, vitamins, amino acids and herbs. They are designed to make a horse more amenable when it is ridden but not all are legal for competition. Because they are not true tranquilizers, any calming effect they have is at a very low level.

Adequately sedating a horse safely requires considerable judgment and experience. In many situations, calling out your vet remains the best option.

Red tape and regulations.

It is well know that horses cannot compete on bute, but not all competitors realise that sedatives are also banned from competition. As with all prohibited substances, it is the owner's responsibility to ensure that their horse's blood is clear of any drug traces by the time they compete. Each drug has a withdrawal time, which is the number of days it takes to be cleared from the horse's system. Withdrawal times for sedatives are typically around three to four days - always much longer than the time during which it has an effect. Your vet can advise on the necessary withdrawal period, but individual horses do vary and if in doubt it is wise to allow an extra day or two.

At present, ACP and detomidine gel are the only sedatives licensed for giving to horses by mouth. This means that if stronger sedation is needed, it will have to be given by your vet. Vets also have the power to prescribe other sedatives that are not licensed for use in horses, but only under certain conditions, and the rules governing theses are strict. ACP tablets are not licensed for horses, for example, but can be prescribed only under very specific circumstances. It goes without saying that injecting in to the vein should only ever be done by the vet.

Case Study - a sore subject

In Spring, the 10 year old cob Digger started treatment for his sarcoids using Liverpool sarcoid cream. Because the cream is a mixture of chemicals that selectively kill the sarcoid tissue, the course of treatment causes increasing inflammation and soreness. With sarcoids both on his sheath and between his back legs, Digger soon became understandably reluctant to have the cream applied.

Initially, a standard level of intravenous sedation was enough to prevent Digger kicking out. But by the third application of the cream, a second top-up sedation dose was needed. By increasing the dose of the opioid alone it was possible to stop Digger objecting without making him so sleepy that he was at risk of falling over.

Cobs can be very smart, however, and Digger soon worked out that if he could avoid being injected then he couldn't be treated either. In his case, applying a twitch kept Digger still for long enough to perform the injection without him getting too worked up. For horses that are unhandled or extremely needle--shy, it can be necessary to give an additional dose of sedative by mouth so they are then calm enough to be injected. The right handler is as important as the medication.

Roger Lee MA VetMB CerEM MRCVS