Although the calming properties of magnesium have been well documented anecdotally, the latest science suggests it may not reliably slow reaction speed responses after all.
Evolutionarily, the horse is a prey animal and as such is a creature of flight. Today when the flight reaction is felt to be excessive some owners opt to use calming supplements, usually containing magnesium.
A previous study of a small number of Standardbreds, published in 2015, showed that magnesium aspartate (a very available source of magnesium) could significantly reduce their average reaction speed response. However, there was a question over whether this would be seen in other animals and even whether the aspartate might have been responsible for this effect because of its action as an amino acid neurotransmitter.
The latest study "Does oral magnesium aspartate supplementation affect reaction speed in horses of different breeds?" was conducted by Charles Sturt University in New South Wales, Australia in collaboration with WALTHAM® Equine Studies Group who provide the science behind the SPILLERS® brand. It aimed to check whether the magnesium or the aspartate was responsible for the 2015 study results and whether these original findings were repeatable.
18 animals (6 ponies, 6 Arabians and 6 Thoroughbreds) were fed three different diets over seven days in a random order. The diets comprised a control hay-based diet providing the National Research Council’s recommendations for Magnesium, this control diet plus the same amount of supplementary magnesium (10g/500kg horse), or aspartate as was fed in the original paper (provided as magnesium aspartate or sodium aspartate respectively).
Some animals decreased their reaction speed and others increased it when fed the magnesium aspartate or the sodium aspartate, compared to showing no significant effects when fed the control diet. At no time did the horses demonstrate any characteristics of being either sedated or more excited when being fed the diets. This indicates that neither the magnesium nor the aspartate had a consistent effect.
Clare Barfoot RNutr, the research and development manager at SPILLERS® commented: “As it stands these results suggest that magnesium supplementation cannot be relied on to modify horses’ reaction speeds. It may be wiser to focus on training and habituation to stressful situations to help manage reactive behaviour, rather than to rely solely on magnesium-based products.”