Riding and working with horses poses some inherent risk of danger, but the risk is greater when working with an aggressive or moody horse.
For this reason, horse owners often look to calming supplements to help make their horse more manageable and easier to train.
Calming remedies are also used during stressful situations such as trailering, showing, farrier work, and veterinary visits.
Despite their popularity, calming supplements may be one of the least studied supplement categories in horses. Behaviour can be hard to quantify which makes it a difficult topic for researchers to study.
Furthermore, the root cause of why your horse is “hot” can be hard to pinpoint. Calming remedies that work for one horse might not work on another horse in a different situation.
Supplements are often formulated based on ingredients with evidence for calming effects in other species, such as humans and mice. However, with limited research on calmative agents in horses, it is difficult to evaluate many of the claims made for equine products.
This results in confusion for horse owners. In a recent survey of Scottish horse owners, 32% reported that they did not know what ingredient in their supplement caused a calming effect and only 40% reported seeing positive results. 
In this article, we evaluate the mechanisms, bioavailability, safety and efficacy of some of the most popular calming horse supplements available on the market today. We also rate the ingredients on the strength of the research evidence in horses.
Anxious Behaviour in Horses
Acute Stress Response
Anxious or problematic behaviours in horses are typically normal physiological responses to stressful or unfamiliar situations. However, these behaviours may be undesirable or dangerous for the rider or horse owner.
Some horses show anxious behaviour transiently during stressful situations such as trailering. These horses may be otherwise calm and only display anxious behaviours in novel circumstances.
Common examples of such behaviours include: 
- Problems loading into the trailer
- Reluctance to move forward
- Refusing to jump fences
Gradual, gentle introduction to new situations is recommended to avoid reinforcing avoidance behaviours.
Trailering and transportation also remove horses from their social group which is naturally stressful for horses. Young horses should be introduced to stressors such as social isolation and trailering gradually with short, progressive exposure to the stressor.
Horses may also identify cues for upcoming stressors. For example, a horse may show reluctance to move forward out of the stall if they anticipate ill-fitting tack or poor riding skills. 
In research studies, trailering has been shown to increase levels of the stress hormone cortisol in the horse’s blood. This hormone increases heart rate, particularly at the beginning of transport.
Taking steps to remove or reduce these types of stressors can go a long way to calming your horse.
The fight-or-flight hormones adrenaline (epinephrine) and noradrenaline (norepinephrine) are also increased during stress and illness. These hormones, as well as cortisol, were found to be elevated in horses with acute laminitis and those with acute abdominal syndrome. 
Some horses develop problematic repetitive, abnormal behaviours that are expressed in their day-to-day life. These are known as stereotypies and include cribbing, stall-walking, weaving and windsucking.
Stereotypic behaviours are commonly thought to be adaptive coping mechanisms that have a soothing effect on the horse. 
In addition to making it difficult to handle these horses, persistent anxiety can have other issues, such as:
- Reduced feed intake
- Weight loss
- Poor performance
- Increased risk of injury
If your horse is displaying stereotypic behaviours, consult with your veterinarian to identify any underlying issues or concerns that may arise due to the repetitive behaviour.
How to Support Anxious Horses
If your horse is displaying unruly behaviour, the first step is to identify any underlying health or management issues that need to be addressed.
Start by evaluating the following possible causes of anxious behaviour:
- Untreated pain
- Lack of turnout
- Lack of exercise
- Pent-up energy
- High carbohydrate feeds
- Digestive distress
- Inappropriate training programs
The most important strategies for supporting calm behaviour in your horse include the following:
- Provide plenty of turnout that enables expression of foraging behaviours
- Ensure your horse’s energy intake is not exceeding requirements by determining needs and weighing feed
- Feed a predominantly forage-based diet with low or no concentrates such as grains or commercial feeds
- If additional caloric energy is needed, use fats instead of carbohydrates
- Ensure your horse’s diet is properly balanced
- Provide enriching, stimulating activities to help prevent boredom
If your horse is still acting “hot” with a balanced diet, adequate foraging, and appropriate exercise, it may be time to consider adding a supplement.
For help with designing an appropriate feeding program that supports calm behaviour, submit your horse’s information online for a free diet analysis by our equine nutritionists.
Top 6 Calming Supplements for Horses
Magnesium is an essential macromineral for all animals. The majority of magnesium in the horse’s body is found in bone and muscle.  This ionic mineral also participates in enzyme activation and muscle contraction. 
Magnesium is used in calming supplements to reduce excitability, anxiety, and reactivity. In human studies, it has been shown to influence nerve transmission and support an anxiolytic (anti-anxiety) effect.
In horses, magnesium deficiency can result in anxious behaviour and supplementation may be beneficial for overcoming low dietary intake of this mineral.
However, it is unclear whether supplementing with magnesium beyond the amount required to avoid deficiency can calm an excitable horse.
Proposed Mechanisms of Action:
- Inhibition of calcium channel thereby causing vasodilation 
- Modulation of the hypothalamus-pituitary-adrenal axis to decrease cortisol production
Bioavailability and Safety:
Magnesium is primarily found in forages including pasture and hay. Moderate-quality hay will generally supply more than adequate amounts of this mineral. 
However, magnesium deficiency can occur with clinical signs consisting of anxiety, poor coordination and muscle tremors.  Other signs of deficiency include excitability, irritability, muscle pain, and sensitivity to sound. 
Magnesium toxicity has not been studied in horses. A maximum dietary concentration of 0.8% has been set. Excess magnesium is excreted in urine. 
Magnesium oxide is most commonly used as a dietary supplement because it provides good oral bioavailability, has an economical price point and a higher concentration of elemental magnesium compared to other sources. This makes it a good option if supplementation is warranted.
Intravenous magnesium sulphate (MgSO4) is effective when administered to horses prior to competition to reduce anxiousness.  Because of its potential to enhance competition performance, it is considered an FEI prohibited substance.
Horses that have received intravenous MgSO4 infusions exhibit a lower head height, which serves as an indicator of sedation. 
Although intravenous magnesium shows a calming effect, oral supplementation has not demonstrated consistent results. Horses supplemented with magnesium aspartate had a reduced reaction time to being startled in one study, but not in another study. 
THE VERDICT: Horses that are deficient in magnesium benefit from supplementation. More clinical research is needed to determine if oral magnesium supplements can consistently produce a calming effect in horses that are not deficient.
Tryptophan is an amino acid precursor to the neurotransmitter and hormone serotonin.
Serotonin is the brain chemical that produces feelings of happiness and contentment.
Proposed Mechanisms of Action:
Tryptophan is thought to produce a calming effect by increasing serotonin levels in the brain.
Serotonin is an inhibitory neurotransmitter that is involved in regulating appetite, sleep, mood balance, emotions, anxiety, pain sensitivity and more. 
Bioavailability and Safety:
Tryptophan competes with other amino acids to cross the blood-brain barrier. In humans, high-dose tryptophan supplementation has been shown to increase the availability of this amino acid in the brain. 
When supplemented at typical levels found in commercial products, tryptophan appears safe for horses.
However, excess dosages may cause restlessness, increased respiratory rate, and acute hemolytic anemia. Signs of toxicity were observed in ponies supplemented with tryptophan at a rate of 350 mg/kg bodyweight. 
Two studies examined the effects of 6 – 6.3 grams of oral tryptophan supplementation in horses. Both studies found no difference in behaviour or heart rate between supplemented and non-supplemented horses. 
In another study, low doses of tryptophan (0.05 and 0.1 mg per kg bodyweight) were found to increase excitability as measured by heart rate and activity level.
This produced the opposite of the intended effect, suggesting that tryptophan supplementation may be more stimulative than sedatory. 
While tryptophan has a calming effect when supplemented in other species, in research studies on horses it has produced a mild excitatory effect. 
THE VERDICT: No evidence to suggest tryptophan promotes calm behaviour in horses.
Valerian (Valeriana officinalis) is a flowering plant commonly used in traditional medicine as a sleep aid and sedative.
The roots of the plant contain active ingredients which promote a calming effect.
Proposed Mechanisms of Action:
Active compounds in valerian produce a sedative effect, including a variety of valerenic acids, most notably sesquiterpene. 
Valerian works by inhibiting the enzyme that breaks down the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the brain. This increases levels of GABA recept activation, inducing a sedative effect. 
Bioavailability and Safety:
The use of valerian extract in horses has not been researched in scientific studies. Caution is advised.
In mice, this herb caused similar sedative effects to the pharmaceutical drug phenobarbital. 
The FEI has placed valerian root on their banned substance list for competition.
Furthermore, the concentrations of active compounds found in valerian preparations range widely. Products targeted to horses are not standardized. 
Although no studies have been conducted on the effects of valerian in horses, studies in other animals demonstrate a calming effect.
One study found that a valerian and passionflower supplement given to pigs during transport had a sedative and anti-anxiety effect. 
Giving a 31.6 mg/kg dose of valeranone to rats produces a mild tranquillizing effect when subjected to a stressor. 
THE VERDICT: Insufficient evidence to determine efficacy in horses. Research in other livestock species suggests a sedative effect, but trials are needed to test efficacy, safety, and dosage requirement in horses.
Thiamin is a B-vitamin (Vitamin B1) that is required by the horse for a variety of metabolic functions, including carbohydrate metabolism.
Proposed Mechanisms of Action: B vitamins play a role in nervous system function and thiamine supplementation is purported to have a calming effect. However, the mechanism of action as a calming agent is unknown.
Thiamine and B-complex vitamin supplementation are generally believed to be beneficial in horses under stress. Thiamine supplementation during sepsis is associated with a better immune response. 
Bioavailability and Safety: Thiamine is readily available in the equine diet from good quality fresh forage.
The amount provided by the typical equine diet is likely sufficient to avoid deficiency for a healthy horse at maintenance to moderate work. Horses in heavy work and horses that are ill may benefit from additional supplementation to meet dietary needs.
Brewer’s yeast is a good supplemental source of thiamine and other B-vitamins.
Thiamine toxicity has not been reported in horses. It is considered safe and is not banned for competition horses. 
Efficacy: There are no published research studies substantiating thiamine’s calming effects on horses. Anecdotal reports suggest that B-vitamin supplements can have a calming effect on horses.
Thiamine supplementation may help horses under stress such as heavy exercise, illness, or travel. However, the average horse will meet their needs from good quality forage alone.
THE VERDICT: Insufficient evidence to validate the effects of thiamine as a calming supplement in horses.
Alpha-casozepine is a bioactive peptide isolated from casein protein in milk that has been shown to reduce anxiety in human and animal studies. 
Proposed Mechanisms of Action: Alpha-casozepine is thought to work similarly to benzodiazepine drugs that are used to treat anxiety.
Bioavailability and Safety:
Alpha-casozepine is generally regarded as safe. Horses supplemented with alpha-casozepine did not experience altered levels of alertness. 
Efficacy: Alpha-casozepine has been found effective for reducing anxiety in humans, rats, cats, and dogs. It was shown to reduce fear in rats during stressful events. 
Cats given this supplement were less fearful of strangers and reacted less aggressively.  In dogs, it produced similar effects to pharmaceutical anxiety drugs such as diazepam and selegiline. 
Studies in horses have been limited but suggest promising early results. In one equine study, feral ponies were supplemented with 1000 mg alpha-casozepine orally once per day for 5 days before being moved to a facility for training for 2 weeks. The ponies continued to receive the supplement for another 2 weeks while being trained.
The ponies were evaluated for calmness and compliance as well as on their progression in learning. The alpha-casozepine supplemented ponies performed better in most of their daily training sessions compared to ponies that were not supplemented. 
THE VERDICT: Evidence of efficacy in other species and preliminary behavioural evidence in horses that alpha-casozepine can induce a calming effect.
Chasteberry has long been used as a traditional herb for hormonal issues in women. It is also growing in popularity as a hormone and mood balance supplement for horses.
Anecdotally, this herb is said to calm moody mares and aggressive stallions.
Proposed Mechanisms of Action: Chasteberry is proposed to work by binding to dopamine D2 receptors in the pituitary gland and decreasing secretions of the hormone prolactin.
Lower prolactin levels result in an increase in luteinizing and follicle-stimulating hormone, which in turn increase progesterone levels.  Elevated progesterone is thought to create the calming effect seen in mares.
The decrease in luteinizing hormone is associated with lowered testosterone levels in male mice. This may be why aggressive stallions are calmed by chasteberry. 
Chasteberry is also purported to help regulate cortisol levels by decreasing pituitary production of adrenocorticotropic hormone (ACTH). Cortisol is the primary stress hormone in the body.
Bioavailability and Safety: Chasteberry extract is comprised of a variety of active plant compounds including essential oils, iridoid glycosides, diterpines, and flavonoids.
Like most herbal remedies, the concentration of these compounds varies based on growing conditions, plant genetics and processing methods.
Chasteberry is generally considered safe for horses but it should not be used in pregnant or lactating mares due to its ability to alter prolactin levels. Consult with your veterinarian before feeding chasteberry to a horse with known medical conditions.
Efficacy: There have been no research studies on the effects of chasteberry in horses. Its usage is primarily based on anecdotal reviews and veterinary case reports which suggest a benefit.
Research from other species suggests promising results for hormonal regulation. More studies are required to determine whether these effects are seen in horses.
THE VERDICT: Insufficient research to determine efficacy in horses. Studies are needed to validate effective dosages and treatment protocols.
Horse owners often reach for calming supplements when their horse is acting up. However, the vast majority of ingredients do not have enough scientific research to validate their use in horses.
This does not mean these ingredients are not effective, but rather that more research is needed to evaluate efficacy. Some ingredients like chasteberry have a strong record of anecdotal evidence for efficacy. But double-blind placebo-controlled trials are required to conclusively determine whether or not a supplement works as a calmative agent.
The supplement with the most promising research-backed calming effect on horses is alpha-casozepine. This casein peptide is safe and was found effective in one small study involving feral ponies.
Ponies given alpha-casozepine were found to be less reactive to stressful situations associated with training and domestic management. Compared to a control group, the supplemented ponies had a higher level of comfort and learned new skills more readily.
Surprisingly, one of the most widely used calming supplements – tryptophan – has not produced calming behaviour in research studies. It appears instead to have a mild stimulatory effect on horses.
Magnesium is another popular calming supplement that appears to be effective when administered intravenously, but there is inconclusive evidence regarding its use as an oral supplement. It may help horses that are deficient in this mineral, but further studies are needed to understand whether it works in horses that are not deficient.
If your horse could use some help with maintaining a calm demeanour, the first step is to address any underlying causes and minimize common sources of stress.
Our nutritionists can help you evaluate your current feeding and management programs to identify changes. Submit your horse’s information online for a complementary review.
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