Magnesium is one of the most important minerals to consider when supplementing cattle.

Magnesium is involved in almost every major bodily function imaginable; over 300 enzyme activation pathways, nerve function, muscle function and excitability, bone mineral formation, hormone secretion, energy metabolism throughout the body, tolerance to stress, health of the immune system, the body can’t even read its own genetic code without magnesium.

Not surprisingly if our cattle are deficient in magnesium the consequences are serious.  The obvious one is grass tetany, which as we all know can result in death and the costs to production systems from dealing with the effects of grass tetany are significant.  Grass tetany can be picked up prior to cows going down by noticing a general increase in cattle’s excitability, reduced feed intake muscular twitching of face and ears and stampeding.

While low levels of magnesium can be a problem, it is often an excess in potassium that is the cause of the magnesium deficiency.  When cattle are grazed on rapidly growing pasture, particularly in cool weather, the level of potassium can be extremely high.  This interferes with the active absorption of magnesium in the rumen.  Pastures fertilised with high levels of potassium and nitrogen make cattle particularly susceptible.  Pastures high in nitrates will also interfere with Magnesium absorption.

To prevent problems associated with magnesium deficiency it is essential to supplement cattle with this mineral and it must be available on a daily basis.  Unlike young stock, mature cattle lack the ability to quickly mobilise magnesium into their blood and so variations in magnesium availability can have a dramatic effect.

Magnesium is not an expensive mineral to supply, its availability from sources such as finely ground magnesium oxide, magnesium sulphate and magnesium chloride is good, chelated magnesium is a dearer option, but highly available.  Supplementation with magnesium s a surer bet that trying to get enough magnesium in through forage.  Availability of magnesium from forage sources is poor.  The availability of Magnesium from Dolomitic limestone should be regarded as nil.

Magnesium is required in large amounts and when potassium is causing interference, the levels needed to overcome the effects of interference are surprisingly high (Weiss, W. P).  This is because we cannot alter the inhibition of active Magnesium absorption due to potassium, so we have to rely on passive absorption.   Schonewille, J.T.( et al,) found that in order to maintain a steady level of Magnesium absorption, Magnesium intake must be increased by 4g/d when the dietary Potassium concentration increases by 10g/kg of dry matter.

Mature beef cows need about 7g of Magnesium per day, equivalent to about 13g/d MagOx or 28g of Epsom salts.  Other than the advantage that these are relatively cheap sources, the other advantage to supplementing with Magnesium is that t is very difficult to overdose cattle with it.  Excess Magnesium is excreted in the urine.

Many Australian farms will face mineral deficiencies and more often than not magnesium will be one of them.  It is not a good idea to rely on blood tests to try and determine deficiencies because a normal blood serum result can hide a lack of available magnesium within the cells of the body which will be affecting cellular function.  Blood tests together with considerations such as the levels of magnesium and potassium in the rest of the diet should be considered, for example if cattle are being offered bore water high in minerals such as magnesium sulphate, then supplementary Magnesium may not be required at all.  If the feed on offer averages levels of Potassium above 1%, then supplementary Magnesium should definitely be under consideration (Weiss, W. P.).

Magnesium can be fed to cattle in a number of ways.  It can be added to a TMR, added to a concentrated grain mix, added to hay or silage prior to baling or ensiling, drenched, added through the water system if troughs are used or offered in a lick.  HCH Genetics offers a basic Magnesium loose lick which is effective and inexpensive as well as loose licks that offer the entire range of required vitamins and minerals. All these options are cheap forms of insurance to ensure optimal herd health.  If you have any questions, don’t hesitate to call on 0429 795 468.



“Quantitative Prediction of Magnesium Absorption in Dairy Cows”  Lit revew

Schonewille, J.T.,  Everts, H., Jittakhot, S., eynen, A.C.

Jounal of Dairy Science, Jan 2008 Vol. 91 Issue 1, p271-278. 8p. 4 Charts

“Plasma Mineral Profile and its Correlation with Reproductive Status in Crossbred cows.”

Devasena, B.1,  Ramana, J. V.1,  Prasad, P. Eswara1,  Sudheer, S.1,  Prasad, J. Rama1,  Intas Polivet. Jan-Jun2015, Vol. 16 Issue 1, p49-53. 5p.

“Liming of two acidic soils improved grass tetany ratio of stockpiled Tall Fescue without increasing plant available phosphorus.”  Hamilton, Elizabeth J.1,  Miles, Randall J.1, Lukaszewska, Krystyna2, Remley, Melissa2, Massie, Matt3, Blevins, Dale G.2,  Journal of Plant Nutrition. Mar2012, Vol. 35 Issue 4, p497-510. 14p.

“Determination of Macroelement Parameters in Different Productive Stages of Simmental Cows.”,  Krsmanović, M.1, Djoković, R.1, Giadinis, N. D.2, Panousis, N.2, Bojkovski, D.3, Savić-Stevanović, V.4, Vasić, A.4, Zdravković, N.4, Korica, S.5, Bojkovski, J.4, Israel Journal of Veterinary Medicine. Mar2015, Vol. 70 Issue 1, p12-15. 4p.

“Macromineral Digestion by Lactating Dairy Cows: Factors Affecting Digestibility of Magnesium”,  Weiss, W. P.1, Journal of Dairy Science. Jul2004, Vol. 87 Issue 7, p2167-2171. 5p. 2 Charts, 2 Graphs.

“Indication of intracellular magnesium deficiency in lactating dairy cows revealed by magnesium loading and renal fractional excretion.”, Schweigel, M.1, Voigt, J.1, Mohr, E.2, Journal of Animal Physiology & Animal Nutrition. Feb2009, Vol. 93 Issue 1, p105-112. 8p. 1 Chart, 3 Graphs

“Nutrient Requirements of Dairy Cattle, Seventh Revised Edition, 2001.” Subcommittee on Dairy Cattle Nutrition, Committee on Animal Nutrition, Board on Agriculture and Natural Resources, National Research Council, National Academy Press, Washington D.C., 2001.

“Nutrient Requirements of Beef Cattle, Update 2000.” Subcommittee on Beef Cattle Nutrition, Committee on Animal Nutrition, Board on Agriculture and Natural Resources, National Research Council, National Academy Press, Washington D.C., 2000.

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