Newsletter February 2017
Dear Horse lover,
It has been an exciting couple of months. Of course we have had Christmas and New Year, I hope you had a good time. Also there was the prize draw to win a copy my book - congratulations again, Linda! Add to that a winter sports holiday for me in the Swiss mountains and we are now well and truly in 2017.
This first newsletter of the new year contains a feature about magnesium by Dr Tania Cubitt for HYGAIN®, an Australian manufacturer of horse feeds and supplements. Magnesium is a mineral that has been popular in horse feeding for years, which is reflected by the number of magnesium-containing products on the market and by the number of websites writing about it. The mineral does get hyped up sometimes and it is refreshing to find more balanced writing such as in this feature.
Have a wonderful time,
Feeding magnesium to horses
By: Dr Tania Cubitt – HYGAIN®
There has been a lot of discussion about magnesium 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 which 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
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 (deficiency of magnesium in the blood). According to NRC, an intake of 20mg of magnesium per kilogram of body weight per day is necessary to maintain normal blood serum levels. 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 deficiencies and excesses
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 0.1-0.3% magnesium with an absorption rate of approximately 40-60%. The maximum tolerable level is estimated at 0.8% of the total diet. Excessive magnesium 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-supplement. For a 500kg horse in light to moderate exercise consuming a total daily intake at a rate of 2-2.25% of its body weight, the maximum intake equates to 80-90g of magnesium in the total diet.
Magnesium sulfate intravenously injected directly affects the heart, forcing it into a state of arrhythmia. When used in larger doses, 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 diarrhoea. The usual form used in animal feeds is magnesium oxide, a fine white powder. Magnesium oxide has an absorption rate of about 50%, 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.
Equine research and magnesium
Magnesium is often fed as a calming supplement and until recently this was an anecdotal practice. A group of researchers in Australia added 10g of magnesium aspartate to horse diets (resulting in a total of 21g magnesium per day including quantities in hay and concentrate). The flight response of these horses was compared to that of horses that had been administered Acepromazine* (at a rate of 0.04mg/kg body weight) and noted similar responses. This was the first study to compare magnesium supplementation to a known sedative agent. It should be noted that urinary calcium excretion was also higher in those horses supplemented with 10g of magnesium. No more than 30g of magnesium should be in the total diet as a safe upper limit.
Magnesium deficiency has been associated with insulin resistance and metabolic syndrome in rodents and humans. Magnesium may also play a role in insulin resistance and other disorders associated with equine metabolic syndrome, but has yet to be scientifically confirmed in the horse. Although there have been anecdotal reports in horses of supplemental magnesium improving insulin resistance, an equine study conducted at the University of Tennessee has found no advantage to feeding a magnesium supplement to insulin-resistant, laminitic horses. This is potentially due to equine diets not unsually being deficient in magnesium.
All of the HYGAIN concentrated or full feeds fed with hay or pasture meet the magnesium requirements for horses set by the Nutrient Requirements Council in 2007.
HYGAIN® is an Australian manufacturer of nutritional supplements and feeds for horses since 1983. Dr Tania Cubitt holds a PhD in Equine Nutrition and Reproduction and is a consultant for horse nutrition.