AN awareness of the true absorption rate of magnesium in supplements will be vital this spring to help mitigate the risk of grass staggers.

Magnesium deficiency is a real threat for lactating dairy and suckler cows at turnout, said David Thornton, Rumenco’s technical manager.

“The low magnesium content of spring grass, between 0.1 per cent and 0.2 pr cent dry matter (DM), plus the fact that it passes through the rumen quicker, all result in very low levels of magnesium absorption from grazing pastures alone.

“Hence the importance of magnesium supplementation prior to and at turnout, to help reduce the risk of grass staggers,” he adds.

However, Mr Thornton highlights that understanding what is included in a magnesium supplement, whether a block, lick or bucket, is important. “There’s limited research to support claims that multiple magnesium sources in a mineral supplement is beneficial to cattle.

“In fact, we know that the more magnesium sources in a magnesium supplement, the greater the risk of magnesium ‘lock-up’ in cattle. This increases the risk of cows developing sub-clinical or clinical cases of grass staggers.

“Therefore, it’s not the quantity of magnesium available, but the reassurance of the true magnesium absorption figure and the particle size of the magnesium source which is important to consider when choosing a magnesium supplement,” he said.

“When you compare two sources of magnesium oxide – a granular and powdered form – the powdered magnesium oxide will deliver a higher rate of magnesium absorption in cattle.

“It’s also important to bear in mind that magnesium isn’t very palatable. Therefore, I’d also advise providing a molassed magnesium supplement to help maintain intakes of this essential mineral,” said Mr Thornton.

By having a complete understanding of the available magnesium in cow diets during key times, and being aware of the benefits and pitfalls of different magnesium sources, farmers can make an informed decision to help manage on-farm risks of grass staggers.