Magnesium: Why Supplementation is Vital

27th April 2021

By Joanne Hay, ECV Nutritionist

With the weather changing and Spring teasing its arrival, grass growth starts to increase with the milder conditions.  It is an important time to ensure that suckler cow mineral requirements, more specifically magnesium, are being met. Magnesium is a crucial mineral for suckler cows, playing a vital role in mobilising calcium from the bones.  In the run up to calving this access to calcium can be key to ensuring a smooth calving.  Any deficiency could be very detrimental, causing metabolic issues such as milk fever.   Magnesium tetany – more commonly known as grass staggers – is caused by a lack of  magnesium. 

Lush spring grass can often be low in this essential major mineral, on average having around 1.6g of magnesium/kg of dry matter.  This can increase the risk of deficiency as low fibre grasses pass through the rumen very quickly, resulting in a decreased uptake of magnesium through absorption.  Cattle being grazed on fields where fertiliser has been applied can have an  increased risk of deficiency.  Both nitrogen and potassium inhibit the uptake of magnesium in the plant which, in turn, reduces the level of magnesium available to the cattle.  Similarly, if housed cattle are fed silage which is high in potassium there can also be a risk of magnesium being less readily available so it is important to ensure correct mineral supplementation during this period.  Magnesium cannot be made or stored in the body so daily supplementation is vital.  By giving cattle access to a constant source of magnesium you can greatly reduce the risk of grass staggers, helping to reach their requirements of 30g/day.

Popular options of supplementing magnesium are molassed mineral buckets, powdered minerals or hi-mag rolls.  Mineral buckets although easy to feed, can be hard to regulate intake so ensuring good access and an adequate number of buckets to number of cows is important.  It is also beneficial to make sure the bucket fed has a high level of magnesium – ideally around 17% - and contains magnesium from more than one source.  This helps to improve availability for   absorption.  Powdered  minerals can be a benefit when feeding housed cattle.  These can be easily fed along with silage, although intakes are also hard to regulate.  Aiming for around 25% magnesium in a powdered mineral will help to ensure requirements are met.  Hi-mag rolls are also a great form of supplementation with 1kg per cow supplying the full daily magnesium requirement of 30g.  Rolls can be easily fed on the ground and feeding cattle daily means intakes can be monitored and any health issues highlighted.  Hi-mag rolls will additionally supply a good source of protein and energy which, if grass is in short supply, is essential to help meet a cow’s nutritional needs.  Our team of  nutritionists at ECV are happy to speak with you about the best and most cost-effective way to reduce staggers risk and supplement your cow’s requirements, to suit your system.

Joanne Hay, ECV Nutritionist
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