A review of the scientific literature available on behaviour modifying feed supplements

2nd June 2020

Who feeds these supplements?

Agar et. al. 2016, investigated the major uses of behaviour supplements in an online questionnaire that was distributed to 820 owners/riders through the British Eventing and British Dressage websites to collect data on the demographics of owners and their horses, the supplements they used, and their opinions on health and performance problems. Owners/riders of dressage horses identified behavioural problems and energy levels as the most important issue in their discipline (42.2 per cent), followed by lameness (37.1 per cent), then back and muscle problems (15.4 per cent). The main issues for eventing were stamina and fitness levels (43.9 per cent), lameness (41.9 per cent), behavioural problems and energy levels (37.1 per cent). This concludes, that around 40% of Sport Horse owners are giving a behavioural supplement to try to improve behaviour and temperament. This is supported by another study, Ross & Roberts, (2018) who found 45% regular use of equine calming supplements in their cross section of Scottish horse owners. Interestingly, Murray et. al. (2018), in Ireland, found a significantly smaller percentage of owners giving calmers (13%), and within this study she was the only one to identify that professionals, more often than non-professionals, were using calming supplements (16% vs 11% respectively). On the basis that Swirsley et. al. reported 50% of owners thought supplements for calming were completely safe and well researched, pressure is mounting to regulate and complete thorough research within the supplement market.

What are our options for managing behaviour nutritionally?

The overriding conclusions are that we should adjust the diet to lower starch and sugar, and increase fibre and oil. The science behind this includes work from Lutherrson et. al. 2009, who completed an in-depth behavioural study into the effects of both types of diets. They concluded that individuals on a high fibre and high oil diet responded less overall (and significantly less violently in their response) to stressful external stimuli and were found to be easier to handle and train. On further blood chemical analysis, they were reported to have higher serotonin levels, lower cortisol, PCV, and heart rates.  The higher starch and sugar diets were correlated to higher incidence of caecal pH acidosis and stereotypic behaviours, like wood chewing and box walking. This research has been available for a long period of time, however, Harris (2005) confirms that many owners are much more willing to try a supplement rather than alter core diet management and training practices.

Let us focus on 3 of the most commonly sought ingredients: -

  1. Magnesium- Magnesium has been report in various studies to have a positive calming effect, as examples by Cardoso et. al (2009), Kaplan and Crawford (2007) and Polezak (2007). Within these studies, much of the research was performed on Mice. Polezak et. al. (2004), first identified that mice deficient in Magnesium exhibited higher levels of anxiety related behaviours. Therefore, through a magnesium high diet they demonstrated a reduction in anxiety and possibly an anti-depressive effect, however, this study used a different source of Magnesium and placed it intra abdominally, so dose and administration would not be directly comparable to equine nutritional studies or current formulations. In Ross and Robert (2018), the survey group found that 59% of respondents found Magnesium to have a calming effect, however, this was purely based on owner opinion. The only other extensive study, in horses, was performed by Dodd et. al. (2015) who fed 11g of Magnesium Aspartate. They found a reduction in reaction rate speed compared to horses that did not receive the Magnesium. It however must be considered that 11g of Magnesium in this project is approximately 10 times higher than the concentration available in most supplements currently on the market, quoted from David Marlin (2019).
  2. Valerian- Valerian supplements are usually sold for the treatment of anxiety, stress, and insomnia in humans. In the equine industry, valerian root extract has been sold with claims of support in relieving nervousness, restlessness, stress, and fear without affecting performance, at a feeding rate of 15 g per day/horse. Ross and Roberts (2018) found respondents described feeding results as inducing a calming effect, thus mitigating undesirable behaviour. Valerian extract contains at least 150 active constituents, with a majority including valepotriates, which comprise valerate, volatile oils, valerenic acid, valeranone, and valerenal, alkaloids and lignans, Elghandour et. al. (2018). Valerian causes a sedative effect by acting mainly as a depressant on nervous system followed by muscle relaxation (Hattesohl et. al. 2008). In a human study, valerian extract at 600 mg/day valued superior to placebo on the Clinical Global Impression scale, with 66% of patients rating valerian effective for sleep in comparison to 26% with placebo (Trevena 2004). Furthermore, the administration of valerian extract at 1,000 mg/kg reduced the sleep latency period in rats (Tokunaga et. al. 2007).
  3. Tryptophan- is a precursor for serotonin, a neurotransmitter associated with aggression, fear, and stress responses. Grimmett & Sillence (2005) and Noble et. al.  (2016) found tryptophan supplementation in horses at low doses, may actually cause mild excitement. More worryingly there has been an association in various species, that the use of Tryptophan in higher doses may reduce endurance and reduce PCV (consistent with Haemolytic Anaemia) through a toxic metabolite, which would be the opposite of what we would consider beneficial in a competition horse.  The reason it was first suggested was due to a human study. Leathwood (1987) found that with a 4x increase in tryptophan there was an 20% increase in brain serotonin, which was associated with increased fatigue and sedation.

Other ingredients for consideration: -

  1. Calcium- There has been no robust study into the effect of calcium on the horse in terms of Behaviour. There are a number of anecdotal statements from owners suggesting their horse is less reactive once on calcium but work still needs to be completed. In scientific fields it is widely thought to be unlikely that a behaviour issue would be linked to a calcium deficiency, as a horse’s diet usually contains adequate levels of calcium. Furthermore, the uptake and regulation in the horse is very well controlled, and understood, so if there were a true deficiency, one would expect much more severe symptoms involving at least muscle and digestive disturbances.
  2. Chamomile- Unfortunately there is little robust scientific evidence, but Adib-Haybaghery and Mousavi (2017) demonstrated that in human studies it may help sleep and reduce anxiety in elderly people.


Within the equine industry, there has been a clear drive to increase research and understanding of why certain supplements work (or are perceived to work). Owner feedback will likely help support an increase in pressure to produce evidence-based research to back up product claims. More research in these areas will help further enhance our knowledge into the needs of horses and what specifically will help benefit their health and behaviour. With that information that is currently available, a clear conclusion can be made that more effort should be made to implement high fibre and high oil diets in horses who show signs of excessive fizziness or “hot” behaviour, as this remains the most compelling evidence we have to nutritionally support increased concentration and decreased adverse reactions to negative stimuli.


  1. Adib- Haybagnery, M & Mousavi, S. The effects of chamomile extract on sleep quality among elderly people: A Clinical Trial, Complementary Therapies in Medicine 2017; 35: 109-14.
  2. Agar, C, Gemmil, R, Hollands, T, Freeman, S. The use of nutritional supplements in dressage and eventing horses. Vet Rec Open 2016; 3: e000154.
  3. Cardoso, C. Lobato, K. Binfare, R. Ferreira, P. Rosa A. Santos, A. et. al. Evidence for the involvement of the monoaminergic system in the antidepressant-like effect of magnesium. Prog. Neurophyschopharmacol. Biol Psychiatry, 2009; 33:235-42.
  4. Davis, B, Engle, T, Ranson, J, Grandin, T. Preliminary evaluation on the effectiveness of varying doses of supplemental tryptophan as a calmative in horses. Appl. Anim. Behav Sci 2017; 188: 34-41.
  5. Dodd, J, Doran, G, Harris, P, Noble, G. 41 Magnesium Aspartate Supplement and reaction speed response in horses. JEVS, 2015; 35: (5) 401-402.
  6. Elghandour, M., Reddy, P, Salem, A, Reddy, P, Hyder, I, Barbabosa- Pliego, A & Yasuswini, D.  Plant bioactive and extract as feed additives in horse nutrition. JEVS 2018; 69: 66-77.
  7. Grimmett, A and Sillence, MN. Calmative for the excitable horse. A review of L-tryptophan. The Vet J 2005; 170: (1) 24-32.
  8. Hattesohl, B. Feistel, B., Sievers, H. Extracts of Valerinana Officinalis L.s.I. Shows an anxiolytic and antidepressant effect but neither sedative nor relaxant properties. Phytomecidine 2008; 15: 2-15.
  9. Kaplan, B. Crawford, S. Field, C. Simpson, J. Vitamins, minerals, and mood. Psycol Bull 2007; 133: 747-60.
  10. Leathwood, P. Food-composition, changes in brain serotonin synthesis and appetite for protein and carbohydrate. Appetite, 1987; 8: 3, 202-205.
  11. Luccherino, L, Franicini, V, Manani, F, Mercurio, C, Santini, F. The emotional and behavioural regulation among two groups of ADHD children: an experience. European Psychiatry, 2014; 29: (1) 1.
  12. Luthersson, N., Neilsen, K., Harris, P., et. al. Risk factors associated with gastric ulceration syndrome (EGUS) in 201 horses in Denmark. EVJ, 2009; 41: 625-630.
  13. Krabbedom, L. Bakker, E. Harnstra, G. Vanos, J. Relationship between DHA status at birth and child problem behaviour at 7 years of age. Prostaglandins, Leukotrienes and EFA 2007; 76: 1, 29-34.
  14. Markus, C, Jonkman, L, Lammers, J, et. al. Evening intake of alpha-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention. Am. J. of Clin. Nut. 2005; 81: 1026-1033.
  15. Marlin, D >> Survey on the effectiveness of equine calmers commonly used in the UK (internet).www.davidmarlin.co.uk/survey-on-the-effectiveness-of-equine-calmers-commonly-used-in-the-uk/. (accessed 13.05.2020).
  16. Matteo, M, Kelly, P, Ariffin, N, Gyon, J. N-3 PUFAs have beneficial effects on anxiety and cognition in female rats: effects of early life stress. Psychoneuroendocrinology 2015; 38, 79-90.
  17. Murray, J, Hanna, E, Hastie, P. Equine dietary supplements: an insight into their use and perception in the Irish equine industry. Irish Vet J 2018; 71.
  18. Noble, G, Brockwell, Y, Munn, K, et. al. Effects of a commercial dose of L-Tryptophan on plasma tryptophan concentrations and behaviour in horses. EVJ, 2008; 40: 51-56.
  19. Polezak, E, Szewczyk, B, Kedzierska, E, et. al. Anti-depressant and anti-anxiolytic like activity of magnesium in mice. Pharmacology Biochemistry and Behaviour, 2004; 78: 7-12.
  20. Polezak, E. Modulation of antidepressant-like activity of magnesium by serotonergic system. J Neural Transm. 2007; 114: 1129-34.
  21. Swirsley, N, Spooner, H, Hoffman, R. Supplement use and perception: a study of US owners. J. Equine. Vet. Sci 2017; 59: 34-9.
  22. Trevena, L. Sleepless in Sydney- is valerian an effective alternative to benzodiazepines in the treatment of insomnia? ACP J Club, 2004; 141: 14-16.
  23. Tokunaga, S., Takeda, Y, Mikimoto, T. Effect of Valerian extract preparation (BIM) on the sleep-wake cycle in rates. Biol. Pharm. Bull, 2007; 30: 365-66.

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