Investigating the impact of oral magnesium aspartate on behaviour, flight reactivity and mineral metabolism in horses.

Magnesium (Mg) is currently marketed in the equine industry as a calmative supplement, claiming to improve focus, promote relaxation and reduce nervous and unpredictable behaviour in horses. On the basis of these claims, horse owners may use products including magnesium during transportation, competition and other new training events. However, despite widespread use, robust evidence of the efficacy of magnesium as a calmative in horses is still lacking. Appropriate dose rates to use for this purpose have also not been reported. The experiments described in this thesis aimed to determine if magnesium can be used as an effective mood stabiliser in horses by treatment of individual horses, of three breed types, with oral magnesium as the compound magnesium aspartate, and reactivity measured. Measuring flight speed reactivity required each horse to be led into a secure race, the lead rope was unclipped and the horse then startled. The horse’s speed of departure over the first 2 meters was measure using electronic equipment. Inductively – coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to determine magnesium concentrations in feed, plasma, urine and faecal samples.
The results of these studies showed that there was no effect of magnesium aspartate on flight speed reactivity at the dose rate of 0.02 g/kg/BW in a group of horses from three different breed groups. However, in a homogenous group of Standardbred geldings supplemented with magnesium aspartate at a higher dose range of 0.02 – 0.03 g/kg/BW there was a significant decrease in reactivity.
Pharmacological profiling of magnesium in both blood and urine using Inductively-Coupled Plasma Optical Emission Spectroscopy showed no difference between treatment doses, and no significant impact on potassium, sodium or calcium homeostasis. Together these results suggest that the efficacy of magnesium supplementation as a mood stabilizer may differ between individual horses and breeds. Therefore, it should not be relied on as an equine calmative at the dose rates studied in this thesis.