Magnesium Overdose & Feeding in Horses
Team Marketing | 06.10.20
There has been a lot of discussion about magnesium overdose and supplementation in horses. It has been reported to have a calming effect as well as being beneficial for obese horses and those predisposed to grass induced laminitis. However, before you go out and purchase a magnesium supplement for your horse we need to understand how magnesium works in the equine body and the potential problems can arise if too much is fed.
What is Magnesium all about?
Magnesium constitutes about 0.05% of the body mass. Sixty percent of magnesium in the body is found in the skeleton and about 30% in the muscle. Magnesium is important in the blood and plays a role as an activator of many enzymes and participates in muscle contractions. Magnesium deficiencies or abnormalities have an effect on neuromuscular function and cardiac tissue. As well as being important for the function of nerve and muscle, Magnesium is involved in the formation of one of the principle components of bone. In addition, Magnesium is necessary for the maintenance of electrolyte balance, particularly for Calcium and Potassium. Magnesium is also a very important as a co-factor in enzymes. Magnesium is primarily absorbed from the small intestine.
Recommended Daily Intake to Avoid a Magnesium Overdose
The normal blood level for Magnesium in horses is 2.2-2.7mg/dl, according to National Research Council in 2007 (NRC), serum magnesium values below 1.6mg/dl are defined as hypomagnesaemia. According to NRC, an intake of 20mg of Magnesium per kilogram of bodyweight per day is necessary to maintain normal blood serum levels and prevent magnesium overdose. Thus, for a 500kg horse in light to moderate exercise, an intake of 10g per day is necessary to maintain blood levels at the minimum value reported.
Magnesium Overdose and Deficiencies
Deficiencies in magnesium can result in nervousness, muscle tremors, incoordination, increased respiration and even death. Many commonly used feed ingredients (e.g. Lucerne, beet pulp) contain about 0.1 to 0.3 percent magnesium with an absorption rate of approximately 40 to 60 %. Magnesium overdosing will be excreted in the urine, but overdoses have been linked to decreased calcium and phosphorus uptake, compromised intestinal integrity, heart conduction problems and renal trouble, so it’s important not to over overdose. The maximum tolerable level in the total diet is estimated at 0.8%, for a 500kg horse in light to moderate exercise consuming 2 to 2.25% BW that equates to 80 to 90g of magnesium in the total diet. Magnesium sulfate intravenously injected directly affects the heart, forcing it into a state of arrhythmia. When a magnesium overdose occurs, it can shut down cardiac function, result in subsequent collapse of the horse, and in some cases, death may occur. This practice should never be done.
The most common form of Magnesium available is Magnesium Sulfate, commonly called Epsom salts, however one side effect of regular feeding of Epsom salts is diarrhea. The usual form used in animal feeds is Magnesium Oxide, a fine white powder. Magnesium Oxide is about 50% absorbable, depending on the relative levels of Calcium also present. The advantage of magnesium oxide is that the body will not absorb it if there is no deficiency, so it is difficult to overdose a horse using this source.