In the spring when the grass is growing faster due to an increase in rain, sunshine and sometimes fertiliser, it produces excess potassium. Potassium slows the uptake of magnesium which horses have a limited ability to store. Magnesium uptake can be aided by the presence of sodium which is why it’s important to have a salt lick available for your horse at all times, but especially so at times of rapid grass growth.
Modern-day diets are often low in magnesium and the high-stress lifestyle of some equines leads to an increased need for magnesium. Areas with acid soils and soft water may not provide enough Mg in water and soil for the needs of performance horses.
Magnesium is a very important mineral. It helps regulate a number of body functions. As well as regulating moods and muscle function, it is essential in regulating some of the metabolic issues inherent in chronically foundered horses, such as blood sugar levels and thyroid. A sign of magnesium deficiency is erratic, or excitable behaviour – magnesium has been shown to reduce reaction times and have a calming effect in this study.
A lack of magnesium has been blamed at least in part for a number of conditions including equine metabolic syndrome and obesity, both precursors to laminitis.
Though it is hard to overdose a horse on magnesium (they get diarrhoea when they get too much), it is important that magnesium and calcium are fed together since they “compete” for the same amino acids, be sure the horse is getting adequate amounts of both. If you feed Speedibeet which is high in calcium, or a small amount of lucerne chaff, that should balance it out.
Which form of magnesium?
Epsom salts (magnesium sulphate) is the least readily absorbed, although some of the magnesium does get taken up by the body so it can be useful in an emergency situation. Magnesium oxide is next best in line. Magnesium oxide is the form found in most feeds because it is the cheapest. More digestible magnesium is in the “chelated” form, ie it has amino acids attached to make it more useable by the body. There are many different chelated magnesium products available and all are better than magnesium oxide in digestibility.
The magnesium in dolomite is as absorbable as that in magnesium oxide but the problem is calcium and magnesium share some absorption pathways and the body preferentially will take the calcium first. If the diet already has an excess of calcium, some of the absorption pathways will be blocked to both calcium and (as a secondary effect) magnesium. This is why it is best to use a pure magnesium supplement first when trying to correct a serious and longstanding magnesium deficiency. Once the symptoms have abated, you should then switch to a supplement program that contains both adequate magnesium and all other minerals in the correct balance.
A good source of an organic chelated form of magnesium is Alleviate, available from the www.gotcha.com.au for the fastest results, and then for a daily maintenance diet, good quality magnesium oxide can be purchased from Balanced Equine.
References: Equine Clinical Nutrition By Lon D. Lewis, Anthony Knight, Bart Lewis, Corey Lewis
Nutrient Requirements of Horses, Fifth Revised Edition, 1989 (1989) Board on Agriculture.