There are occasions when a rider/owner/trainer might need to calm their horse in preparation for stressful situations. This could be for the farrier, during stall rest or transport, prior to veterinary care, or even riding in a new environment.

However, if a compound is fed or administered to alter mood or behaviour at a competition, it is forbidden by the FEI, Equestrian Canada, and the US Equestrian Federation. The mission of all these bodies is to support fair play/clean sport and to “place equine welfare above all other considerations [and] abstain from the use of performance-enhancing substances or methods” (EC’s Code of Conduct and Ethics). This is regardless if a product “tests positive” or not.

Of course, this becomes a slippery slope, particularly when we are looking at nutrients (magnesium or tryptophan, for example). It was a topic that I discussed with the chief administrator of the USEF Equine Drugs and Medications Program, Dr. Stephen Schumacher, at the recent American Veterinary Medical Association meeting in San Antonio. As he explained, it comes down to intended use – if you administer your horse an added nutrient such as magnesium or tryptophan with the intention to alter your horse’s mood or behaviour at a competition – it goes against the balance of competition and it is no longer a level playing field.

Drugs such as acepromazine are not “feed supplements” and therefore won’t be discussed here. Similarly, other injectable compounds such as ACTH (adrenocorticotropic hormone), dexamethasone or GABA (gamma amino butyric acid) have been used as calming agents for horses, but scrutiny for these is high due to some recent horse deaths. GABA may also be fed, but again is currently on the USEF list of banned supplements and even having GABA or injectible magnesium on your possession is a violation of EC competition rules. The herb valerian (valerenic acid) is often used for its calming effects, but is also on the prohibited substances list.

Common Calming Supplements

Non-nutritive feed additives commonly found as part of calming supplements include zylkene, inositol and lecithins. Zylkene (alpha-casozepine) is derived from milk, and has been shown to have some benefits in terms of improving behaviour and handling horses for potentially aversive health care, or during basic training for semi-feral horses. (For more on Zylkene, see “Keep Calm and Carry On” in the May issue.) The compound inositol, which is a type of sugar (and often mislabeled as a vitamin), is commonly found in equine calming supplements, but research into its effectiveness is lacking. Lecithins are a type of lipid found in many plants, but may be added to calming supplements. One study reported that when lecithins were fed as part of a high-fat diet, horses showed reduced “spontaneous activity.”

Essential Nutrients

Nutrients by definition provide sustenance for the maintenance of life, and some of these include compounds such as magnesium (an essential mineral) and tryptophan (an essential amino acid, a component of protein that the body cannot synthesize on its own). When deficient, various disease states can develop; likewise in some cases of toxicity.

Magnesium is a component of bone, provides stability for the energy compound adenosine triphosphate (ATP), and acts a cofactor in several enzymatic reactions. It has been suggested that magnesium deficiency results in increased anxiety in humans, and indeed magnesium supplementation may lessen these effects.

In horses, magnesium deficiency is very rare. The magnesium requirement of a 500-kg mature idle horse is only 7.5 grams. The lowest amount of magnesium reported in 82,000 samples of grass hay analyzed by Equi-Analytical was 0.116%. Therefore, if a horse only ate 1.5% of its body weight as hay (7.5 kg in this example), he would already be consuming more than he needs at 8.7 grams.

Of course, horses in work would have higher requirements, but they are also typically consuming more feed. In fact, when horses are fed good-quality hay, commercial concentrates, or cereal grains, their magnesium status is typically at 2-3 times their requirement. When a horse is further supplemented, amounts of 6-8 times the requirement have been observed.

It should be noted that calcium may negatively affect magnesium absorption within the digestive tract, and both Ca and Mg can bind the same sites within body membranes. Therefore, there is some emerging evidence in humans that excessive calcium intake along with low magnesium status may exacerbate anxiety symptoms. Little research has been conducted regarding the interactions of minerals in horses. Regardless, a well-balanced diet, formulated to meet both calcium and magnesium requirements, is ideal.

Tryptophan is an essential amino acid, and is a precursor for serotonin, a neurotransmitter that is often associated with “happiness.” Many classes of antidepressants for humans function by preventing serotonin breakdown. Because it is a normal component of a horse’s diet, supplementation is believed to be more effective when administered separately several hours after a meal (or before exercise, typically via a paste.) There are no studies that have reported solid evidence of its efficacy to calm a horse.

Other calming ingredients include some of the B-vitamins, most notably thiamine (vitamin B1). In humans, thiamine deficiency has been associated with aggressive behaviour, thus there is some reasoning that ensuring adequate levels are in the diet will help prevent this. However, there is no published evidence to support that thiamine supplementation results in calming behaviour, and in fact there is only one report in the human literature that suggested a positive effect of reducing anxiety, although this study only had nine subjects.

Thiamine in the equine diet is plentiful, and the microbial organisms of the horse’s digestive tract that produce thiamine and other B-vitamins appear to do so sufficiently such that deficiency is exceedingly rare.

Strategic Feeding the Key

As indicated, a well-balanced diet will be your best bet for optimal performance. Dietary choices and timing of feeding may also help. For example, several studies have reported that feeding less sugar in a horses’ diet reduces spontaneous activity. Similarly, feeding several hours (>4 hrs) prior to exercise may help prevent swings in metabolite (most notably glucose) concentrations during exercise, and may make for a calmer horse. A balanced diet and strategic feeding plan is a “clean” way for optimal behaviour and performance.


A list of the equine drugs and medication control regulations developed by the Canadian Pari-Mutuel Agency (CPMA) which EC follows can be found here.

The Equestrian Canada rules for Equine Medications Control can be found in the EC Rules Section A: General Regulations, Equine Medications Control – Chapter 10, Articles A1001-A1014, here.

The FEI’s 2016 Prohibited Substances Lists here and here.