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Supplement manufacturer claims that multiple magnesium sources in a mineral are better than one are unsubstantiated and actually contradicted by published research studies.

“Farmers should be wary of mineral supplier claims, particularly with respect to the magnesium supplements that are sold at this time of year to reduce the risk of grass staggers,” says Rumenco technical manager David Thornton.

“There are few, if any, controlled ruminant studies comparing different magnesium sources under the same conditions. Interactions with other minerals, such as potassium and sodium, will also affect magnesium availability. And the more magnesium sources in a mineral, the greater the level of potential magnesium ‘lock-up’ problems,” he warns.

Mr Thornton does add that there is one published study that has ranked the absorption percentages of 10 different magnesium sources, but the take-out message is misleading.

“The magnesium absorption range of the different mineral sources was actually quite narrow at 35-57%. And when you consider that the sources absorbed best were those never used in proprietary supplements on cost and low magnesium concentration grounds, you have to seriously question the whole ‘multiple magnesium source’ marketing message,” he says.

Mr Thornton says what farmers really should be looking for reassurance on is the true magnesium absorption figure from the mineral to be fed and the particle size of the magnesium source. These factors are far more important.

“Particle size in a magnesium source is vital. For example, when you compare the two magnesium oxide (Cal Mag) sources – in granular and powder form – the powdered Cal Mag delivers a higher magnesium absorption in the animal,” he says.

Molassed, weatherproof buckets and blocks supplemented with the right ‘fine particle’ single magnesium source should be fed free-access at grass. No troughs are needed and these types of supplements are available 24/7. They also prevent bullying and save feeding time and labour. Bear in mind too that magnesium is not very palatable, so being molassed, bucket and block products do help maintain the necessary intakes of this essential mineral, Mr Thornton says.  

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