Nutrition CPD May 2016


Keep calm and feed a calmer?

What do calmer supplements contain? And what research there is that they actually work? Vet Becky Lees has the answers.

Horses evolved as flight animals to stay safe by running away from predators. However, since modern horses are usually unable to run away from what scares them, considerable stress and anxiety can be suffered. 

Some horses find particular events stressful, such as vet and farrier visits, travelling or clipping. Others can be stressed by their management; for example a horse who dislikes being without company being stabled out of sight of other horses. 

Stress manifests in many different ways which are perceived as undesirable behaviour. It may become dangerous as the horse adopts more desperate behaviour to avoid what he is scared of. Stressed horses represent poor welfare, underperform and may develop vices. 

Calmers are presented as powders, liquids and syringe pastes.

Training and environment

Training works best for horses that react to particular stressful events, such as loading onto a trailer. Environment modification is most successful for horses with longstanding stress. 

A holistic attitude is needed to look at the horse’s management, feeding and routine and to establish the likely cause of stress. Then appropriate steps can be taken. Retailers may wish to suggest seeking professional help.

Pain or stress?

Some behaviours can be due to pain rather than stress. For example, a horse may not want to hold up his feet because he has joint pain. In these cases, veterinary attention is required. Some horses find certain events, such as clipping, so stressful that prescription drugs are needed to sedate them. 

How can calmers help?

Calmer supplements are incredibly popular with horse owners. They are most effective when used alongside training and environment modification. But how do you recommend a product when there are so many on the market, all claiming to have excellent results? 

Here are the key questions to ask when choosing which calmer supplement to recommend:
• What does the supplement contain?
• Will the horse be safe to handle and ride when it is on the supplement?
• Could it cause any adverse effects or affect performance?
• Is there any evidence that it will actually work?
• Is it legal for competition?

Most horse owners are aware of what causes their horse to be stressed and calmer supplements are ideal for use in these situations. However, they shouldn’t be given as an excuse for poor management and are best used alongside training and environmental management. There are always going to be certain times when we can’t completely prevent stress and calmer supplements have a definite place for use during these times.

Powder, liquid or syringe?

Powders and liquids are designed for daily maintenance use or for use over several days during a potentially stressful time, such as moving yard or around bonfire night. Syringe pastes are designed as a ‘top-up’ for specific stressful events, such as clipping.

Supplements containing magnesium

Magnesium is important for brain function as it’s involved in neurotransmitter synthesis and receptor binding. Magnesium depletion in horses has been associated with brain malfunction and a heightened stress response.7 

Unfortunately, blood magnesium concentration is an insensitive indicator of magnesium intake.8 There is some evidence to show beneficial calming effect, one study found that magnesium supplemented horses had lower heart rates in stressful situations², however further research is needed to prove the benefit of magnesium in a calmer supplement. 

Magnesium is safe, with no adverse effects as the levels in horse feed when combined with calmer supplements will not cause an imbalance. However horses are not able to absorb some magnesium compounds, so magnesium calmers need to be chosen carefully.

To have any effect, the magnesium calmer supplement must be bioavailable. This simply means it can be absorbed by the horse into the blood. 

Magnesium oxide is extremely poorly absorbed¹ and should be avoided. Magnesium sulphate and magnesium chloride have low bioavailability. Chelated magnesium and magnesium aspartate hydrochloride have the highest bioavailability, so these are what you should look for in a calmer supplement. 

There is no benefit to having more than one magnesium compound in a supplement.

Magnesium topical sprays should be avoided as magnesium compounds are not absorbed through the skin. This also means that they are not absorbed into the blood and therefore won’t work. Any effect will be due to the placebo effect only (see box). 

The placebo effect

A placebo is an ineffective treatment for a medical condition intended to deceive the patient. When patients given a placebo have a perceived or actual improvement in a medical condition this is known as the placebo effect. The placebo effect can work on animals too.5

For example: A horse is being difficult when ridden, shying and napping. The owner puts the horse onto a calming supplement and the horse’s behaviour dramatically improves. Is this due to the supplement, or the owner’s belief in the supplement which means that she is more confident when riding the horse with the result that the horse does not misbehave? 

This is why proof that a supplement works from published peer-reviewed research is so important! Unfortunately there is little published research about calmer supplements in horses due to the high costs of running studies. It’s also extremely difficult to design a study that will give statistically significant results.

So, we are left with the following conundrum:
If a calmer appears to work – by real or a placebo effect - and has no adverse effects on the horse, then using it will actually give a real and beneficial effect to both horse and owner. So does it matter whether the effect is real or due to the placebo effect?

Supplements containing herbal extracts and/or tinctures

Many supplements contain a variety of compounds. These may be dried herbs, a purified extract or as a tincture (alcoholic extract). Unfortunately research in horses is very limited.

These are some common herbal compounds:

• Valerian: This is a plant remedy used for insomnia in humans. It has been shown to have a sedative activity in mice and is assumed to have a sedative action in horses, although no research has been carried out. Anecdotal reports of its use in horses suggest a sedative effect, however it may affect coordination and horses given valerian may not be safe to ride. The amount of active ingredient (valerenic acid) can vary in supplements and it can enhance the effect of tranquilisers and anaesthetics. Valerian can cause diarrhoea and colic. Overdose can cause excitement or overstimulation. Valerian is a prohibited substance under FEI rules and should not be used in competing horses.

• St John’s wort: The active ingredients in St John’s wort are hypericin and hyperforin. Research has demonstrated a positive response for mild to moderate depression in humans. There is no research in any species that demonstrates any effectiveness for stress or anxiety, so it’s unlikely to be of benefit in a calmer supplement. St John’s wort can interact with a number of prescribed medications. Higher doses can cause severe photosensitisation (sunburn) in all species.

• Hops: There is a small amount of contradictory research in humans that suggests a sedative effect at higher doses; however no equine research exists. Hops have no adverse effects.

• L-tryptophan: This comes from plant or synthetic sources and is an amino acid precursor of serotonin (a neurotransmitter). The response to L-tryptophan depends on species. In humans, dogs, pigs, poultry and fish, it has been shown to decrease aggression. In calves, vixens and poultry research shows it may reduce fearfulness. However, behaviours linked to excitability are not modified in any species³. Recent research shows that it is absorbed by horses and that there are no beneficial behavioural effects. In horses, low doses were shown to actually cause mild excitement while high doses can reduce endurance capacity and cause acute haemolytic anaemia³. L-tryptophan is included in many calmer supplements, however this research suggests that products containing it should be avoided.

• L-Theanine: This is an amino acid derived from green tea. In humans it is thought to have an anti-stress effect without causing drowsiness or affecting coordination by increasing GABA and dopamine levels in the brain – the ‘happy chemicals’. There has been no research looking at whether it has the same affect in horses. It has no adverse effects.

Supplements containing calcium compounds

There is no evidence linking calcium deficiency with anxiety or behavior problems. Grass and hay are high in calcium so deficiency is incredibly rare. There is absolutely no evidence that calcium compounds have any effectiveness as a calmer supplement, so any effect will be due to the placebo effect only. 

Supplements containing milk

These are derived from a milk protein called casein, a molecule known to promote relaxation of newborns after breastfeeding. There is some research in horses showing that it can be beneficial in combination with behaviour modification and training programs.4 It has no adverse effects.

Supplements containing B vitamins

Many calmer supplements contain B vitamins; however no research exists to see if they are beneficial. B vitamins assist the maintenance of nervous system functions and deficiencies create nervous system effects. Without any research it’s impossible to tell whether they are beneficial; however they have no adverse effects.

Helping customers decide

With so many calmer supplements on the market, it can be incredibly difficult for SQPs to know which one to recommend. 

Read the ingredients section on the label so that you can help the horse owner understand what each ingredient does. The customer should be happy that the supplement chosen will have no adverse effects, be bioavailable to the horse, have as much evidence for effectiveness as possible and be legal for competition.

1. Coenen M. Macro and trace elements in equine nutrition. In: Equine Applied and Clinical Nutrition. Saunders. 2013. 191-228.
2. Dodd JA, Doran G, Harris P, Noble GK. Magnesium aspartate supplementation and reaction speed in horses. 2015. 35(5): 401-402.
3. Grimmett A, Sillence MN. Calmatives for the excitable horse: a review of L-tryptophan. Vet J. 2005. 170(1):24-32.
4. McDonnell SM, Miller J, Vaala W. Calming Benefit of Short-term Alpha-Casozepine Supplementation during Acclimation to Domestic Environment and Basic Ground Training of Adult Semi-Feral Ponies. Journal of Equine Vet Science. 2012. 33(2): 101-106.
5. McMillan FD. The placebo effect in animals. JAVMA. 1999. 215(7): 992-999.
6. Noble GK, Brockwell YM, Munn KJ, Harris PA, Davidson HP, Li X, Zhang D, Sillence MN. Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses. Equine Vet J. 2008. 40(1): 51-56.
7. Stewart AJ. Magnesium disorders in horses. Vet Clin North Am Equine Pract. 2011. 27: 149-163.
8. Stewart AJ, Hardy J, Kohn CW, Toribio RE, Hinchcliff KW, Silver B. Validation of diagnostic tests for determination of magnesium status in horses with reduced magnesium intake. American journal of veterinary research. 2004. 65, 422-430.