$THERE is an enormous amount written about the link between feeding and behaviour, and the ‘calming supplement’ market is sizeable. However, there is in fact very little direct research in horses that investigates how diet impacts on behaviour if at all. One of the most basic ideas to consider is whether the anecdotal practice of placing horses that can be excitable or even unruly, such as those in pre-training, on a low energy, high fibre, low starch diet. Certainly the amount of energy fed per day, irrespective of the energy source, is thought to affect behaviour in some horses. When an excess of concentrate feed is fed in horses that are confined for a large part of the day or where exercise is light, horses may pile on the pounds, or can express this excess energy intake through their behaviour in terms of excitability or fractiousness. Research by Dr Nell Davidson concluded that stabled horses fed a ration of forage only were less restless and more co-operative when being handled during light work, compared with those fed forage and cereals. A French study of showjumpers fed a ration that was lower in starch, higher in oil, and supplemented with magnesium, tryptophan, and B vitamins exhibited a reduced fear response and reactivity as well as lower heart rates in response to controlled stressful situations when compared to a high starch, low oil ration of similar energy content. Whilst resting heart is often viewed as a reflection of state of fitness, it can be very variable due to the effect of excitability. Research conducted by Doctors Erica McKenzie and Stephanie Valberg whilst investigating tying up showed that horses that were fed a low starch, high oil diet at a high level of energy intake similar to horses in training, exhibited lower pre-exercise heart rates and had a calmer demeanour compared to those that were fed a ration with a higher starch content. A step down in the quantity of concentrate feed and the starch content may be worth trying with an excitable horse before reaching for the supplement tub or bottle. The practice of maximising good quality forage intake and complementing with a low-to- moderate energy, low starch, and high fibre feed would seem to stack up for excitable horses. In these animals, where more condition is required as training progresses, a high oil feed or supplement can be used. For tying up, rations that are low in starch have been advocated for many years by veterinarians to help reduce the likelihood of further attacks. However whilst successful in some receptive horses, the explanation for heir benefit is less clear. It has recently been suggested that a ‘low starch’ contributes towards reducing anxiety and stress in these animals, which is now widely considered as a potential trigger for tying up in susceptible animals. The level of forage fed and/or fibre content of the diet also appears to have an impact on other aspects of equine behaviour. Stereotypic behaviours such as wood chewing and wind- sucking are known to be more prevalent in meal-fed horses exposed to diets that are low in forage and high in starch. This perhaps is not surprising, as this type of diet is very far removed from a horses’ natural diet and may frustrates their psychological need to chew. It has also been suggested that some of these oral stereotypic behaviours stem from the desire to stimulate saliva production in an ongoing attempt to buffer gastric juices, especially in horses wit gastric ulcers. However, whilst there are some horses that perform these behaviours that may have gastric ulcers, there are many others that do not, and the stereotypic behaviour may have developed as a coping mechanism for another stressor. There are many additives that are proposed to have carminative effects in horses, and which are commonly found in supplements marketed as calmers. Few of these have any substantive scientific evidence in horses to support their reputed effects. The rationale for the use of some additives such as B vitamins and magnesium largely comes from the symptoms of severe deficiency, which can include nervousness, excitability, and irritability. However a horse in training that is fed a good ration is unlikely to be severely deficient in these micronutrients, and the benefit of hyper-supplementation has not been investigated in horses. Magnesium-based calmers represent a large chunk of the calming supplement market and so anecdotally this perhaps suggests that they have some effect in a proportion of horses. Equine scientists need to evaluate the effect of magnesium supplementation further especially as there is some interesting research in other species. In mice, for example, it is suggested that magnesium may have anxiolytic (anxiety reducing) and anti- depressive effects when fed at a comparable level per kilogram of bodyweight to that found in some equine supplements. Additionally in humans, magnesium shows a beneficial effect when supplemented in combination with vitamin B6 (pyrodoxine) in women with pre-menstrual syndrome. Tryptophan is another frequent ingredient in equine calming supplements and is an essential amino acid involved in the synthesis of the neurotransmitter serotonin. Serotonin is involved in the mechanism sedation and also inhibits aggression, fear, and stress in some species. The response to tryptophan is quite varied between species and seems to be affected in other animals by factors such as age, sex, and level of exercise. There are no studies to date that confirm an effect of tryptophan in horses as a calmer. The herb valerian is pharmacologically active and has been shown to have both sedative and anxiolytic effects. It contains a number of constituents that may contribute including isovaleric acid and GABA (a neurotransmitter). Its mechanism of action is believed to be due to the ability of one or more constituents to bind to the same receptor sites in the body as the psychoactive drug benzodiazepine (e.g. Valium). Despite few if any studies on the effect of valerian in horses, its established pharmacological action has led to it being considered as a prohibited substance in both racing and other equestrian disciplines for many years, and one or more of its active constituents form part of the post- race drug screen. Other herbs such as chamomile, hops, and lemon balm feature in equine calming supplements although again, there is little scientific evidence of efficacy specifically in horses. Lecithin is a mixture of various lipid-like substances including phospholipids, which can be extracted from oilseeds such as soya. Its primary use in the feed industry is to enhance absorption through its actions as an emulsifier. Interestingly in horses, soy lecithin has been shown to have an effect on behaviour by reducing reactivity and spontaneous activity when combined with corn oil. However, the amount of soy lecithin used in this study was relatively high (oil: lecithin ratio of 1:1 fed at 10% of feed intake) and it may be beyond the scope of most dietary supplements to deliver such an amount. Whilst strictly not a nutritional ingredient, there are a group of topically applied products that harness the science of pheromones in their formulation. Equine appeasing pheromone (EAP) is a substance that is produced naturally in mares following foaling, which helps calm and reassure foals to allow early bonding with the mare. There have been a couple of interesting French studies published in 2006 and more recently in 2011 reporting that a synthetic version of this substance can be topically applied in horses (by aerosol spray application to the nostrils) to reduce fear-based behaviour and heart rate response to stressful situations. The size of the equine calming supplement market is no doubt an indication of the perception of behavioural problems in horses, but there is a lot more work to be done in evaluating both the safety and efficacy of both nutritional strategies and supplements. It is a particularly difficult area to evaluate especially as although calmness may be desirable, severe sedative effects are clearly a step too far as they may impede a horse’s ability to exercise safely and perform to the best of its ability.$

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