However well you manage horses, they are all individuals. Just like people, some horses in some situations become stressed and anxious. This may be due to genetic influences, previous unpleasant experiences, or management. Once horses become anxious they may develop behaviors that make managing them difficult or even unpleasant for the horse and the owner, such as rearing, shying, biting, pulling, barging, etc. Animals that have erratic or difficult behavior can be more likely to injure themselves or people working with them. It can also make them hard work to manage and everything becomes a challenge from riding, shoeing, clipping, travelling, etc - tiring for the horse and tiring for the owner. For most horses, exhibiting erratic or difficult behaviors also affects their health and performance in competition.

In some animals, the stress or anxiety is a contributing factor in the development of stereotypical behaviors such as wind-sucking, crib-biting, frequent pawing or stamping and box-walking. Successfully managing stress and anxiety in horses can make life easier, more enjoyable and more productive for the horse and rider, trainer and owner. When we manage horses for riding, competing or breeding, we present them with a very different environment to that in the wild. Some of the changes in these horses compared with horses in the wild may include reduced interaction with other horses, less space, being stabled, artificial diurnal (daily) rhythms that we impose through our management, larger less frequent feeds and restricted grazing. Of course there are many advantages to the horse of domestication, including potentially improved health (vaccination, worming, etc), protection from predators and access to plenty of food and clean water. But despite all this, the horse is still a “flight” animal. Its first reaction to any new or frightening experience is to run away.

There are various approaches that we use to help us manage difficult horses. Sometimes taking a horse away from something that seems to cause it anxiety can help. Sometimes a simple change in management can help. For example, removing a horse from a group where it is being “bullied”. Sedative drugs such as acepromazine (ACP, Sedalin), xylazine and romfidine are very effective for short-term management but they do not address the underlying problems of anxiety. Sedatives also commonly affect gait and coordination which may lead to decreased performance and even increased risk of injury. Of course for good reasons drugs such as these are prohibited in competition. Sedatives are also powerful drugs and like any drug can have unwanted side effects. When used under veterinary supervision for the right indications, sedatives are usually very safe and effective but they are unlikely to be a suitable medium or long-term solution to behavioral problems.

There are currently an immense number of calming supplements available in the marketplace. There is clearly a demand by horse owners for products that can be purchased without the need for a veterinary prescription. But how much evidence is there to support the effectiveness (efficacy) of these products? Sadly, very little. To carry out appropriate clinical or scientific trials is usually very costly so these are rarely done. Often we are left with the adverts that seem very compelling and use all the right words or testimonials from well-known riders or trainers extolling the virtues of a particular calmer. When a vet gives a horse a good dose of a sedative, the owner will clearly see the result in minutes with their own eyes. But can you really see this effect with your calmer? In many cases the owner wants to see an effect even if there is not one there – the placebo effect. Especially as according to the manufacturer’s instructions many products require prolonged periods of feeding, in some cases several months, before they say an effect can be expected.

So, recognizing that horses do develop certain behaviors which we consider undesirable and that they are also frequently exposed to new or stressful experiences and that some horses are more susceptible to stress than others, an ideal calmer should be able to:

1. Rapidly reduce acute stress
2. Be able to reduce overall anxiety in the medium to long term

This should potentially allow the horse to be able to:

1. Learn better
2. Adapt faster
3. Improve more
4. Have a lower risk of developing stereotypical behaviors
5. Have a lower risk of stress-related disease (e.g. infection, gastric ulceration)

So let’s look at some common equine calmer ingredients and see how they might work and any evidence for effect in horses.

Magnesium Probably the most common calmer ingredient. Some magnesium calmers claim to have a “better” source of magnesium than others. This sounds good but is of little significance as there is no scientific or clinical evidence of any calming effect of magnesium. Studies in mice suggested that supplementing with magnesium could have an antidepressant-like and anxiolytic-like (anxiety reducing) effect. However, the amount of magnesium given was very high and was given directly into the body cavity by injection and not fed to the mice. A different study in mice showed that feeding a deficient magnesium diet produced an increase in anxiety. However, magnesium deficiency in horses is rare and most diets contain adequate magnesium. There are currently no published scientific studies demonstrating a calming effect of magnesium supplements in horses. Magnesium supplementation can also interfere with calcium balance and lead to an increased risk of orthopaedic problems. Interestingly, magnesium is not on the FEI Prohibited substances list which should give an indication as to its likely efficacy.

Tryptophan Tryptophan is an amino acid and is another common active ingredient in equine calmers. Tryptophan is a precursor for serotonin, a neurotransmitter that has been associated with aggression, fear, stress and inhibition of aggression in a variety of animal species. There appear to be many factors that determine the response to tryptophan and few studies have been carried out in horses. Those that have suggest that low doses actually cause mild excitement as opposed to calming. Higher doses reduce endurance and can cause haemolytic anemia (lowering of red blood cell count). An Australian study into the behavioral effects of tryptophan on horses published in 2008 concluded that “Plasma tryptophan increases when tryptophan is administered at a dose used in some commercial products, but this is not reflected by marked behavioral changes in the horse”. Again, like magnesium, tryptophan is not on the FEI Prohibited substances list.

Valerian (Valerenic acid) There is a reasonable amount of scientific evidence to suggest an anxiolytic effect of Valerian (Valerenic Acid) an extract from Valerian plants. However, there are no scientific published studies of Valerian or its extracts in horses, but interestingly Valerenic acid is on the FEI Prohibited substances list.

Summary There are calmers on the market that contain “active” ingredients other than these. At present there is no scientific evidence in the form of published, peer-reviewed studies to support the effectiveness of any of these active ingredients. This is desperately needed. Supplements are far from cheap and you should ask yourself if the products you are using really do work or whether any effect is due to “the placebo effect”. That is you paid for it, you want it to work, you believe its going to work and you might even be convinced it has worked. Whether it really works or not is a different matter.