Mineral Series in association with Terra NutriTECH

Hypomagnesemia is the technical term for what is more commonly known as grass tetany. It is characterised by a subnormal level of magnesium in the blood and is generally associated with grazing.

Typical symptoms of grass tetany are reduced milk yield (up to 15% loss of production), nervousness and muscular tremors.

In the acute form, the cow staggers around, froths at the mouth, collapses and dies.

Research shows that cows have low stores of magnesium in their bodies. Getting an adequate amount of magnesium is shown to have a positive effect on reducing grass tetany. While it’s evident that cows have magnesium in their bones, they can only mobilise this very slowly.

Cows are typically poor at absorbing magnesium which means they require daily intakes of magnesium. Lactating animals during this season have an increased requirement for magnesium also. Anything that affects the gut function or DMI (dry matter intake) can disrupt magnesium absorption.

What are the risks involved with grass tetany?

  • Certain swards will be poorer at taking up or storing magnesium. Clover swards are better at taking magnesium, while lush ryegrass swards can be poorer;
  • Fertiliser applications can affect uptake. Potassium will lock up magnesium and also nitrogen fertilisers will lead to more ammonia in the rumen which may affect magnesium uptake;
  • Anything that affects DMI (dry matter intakes) can disrupt daily intakes of magnesium. So adverse weather can play a role where we need to be extra vigilant when the weather changes in spring;
  • Stress causes a redistribution of magnesium in the cow’s body, increasing the risk. This can also be seen in suckler cows sometimes in autumn time at weaning due also, to lower DMI at this time;
  • Spring grass can be lower in fibre and high in oils (fats like CLA) which can lead to increased gut transit times and potentially lower absorption rates of magnesium. These all make grass tetany high risk during spring grazing.

What are the causes of grass tetany?

The main causes of grass tetany are:

  • Magnesium deficiency;
  • Poor feeding intake;
  • Cold and wet weather;
  • Animal stress at weaning;
  • Animal stress at bulling;
  • High potash (potassium) applications.

What treatment is available for tackling grass tetany?

  • It is always cheaper to prevent than to cure;
  •  The recommended treatment is the administration of intravenous magnesium sulphate for emergency use and cows need to be treated very quickly to prevent loss.

It is recommended that a vet should administer magnesium sulphate in these cases.

How to prevent grass tetany? 

We know cows need daily intakes and the spring season poses some increased risks. We need to ensure magnesium supplementation during this key risk period.

Supplementing dairy cows:

  • Magnesium can be given through water. This is the most effective way of ensuring adequate mineral intake specifically suited to the needs of your herd. It is cost-effective and reduces the intensity of labour requirements;
  • Magnesium in concentrates being added to feed – but be careful to allow for this when reducing meal in the diet;
  • Magnesium boluses are an option that can be used but they only cover for three weeks. This is a labour intensive method and care should be given if animals ‘cough up’ bolus in following 24 hours;
  • Palatable licks and high magnesium buckets;
  • Feed fibre in the diet during the spring to reduce the risk from lush spring grass high in oils and low in fibre. Most care should be taken when lush low covers are being grazed in particular;
  • Pasture dusting magnesium can be done also but is very labour intensive.

Terra NutriTECH recommends using magnesium through our OPIS or ORBVIE technologies, as accurate dispensing to ensure all animals get an even amount is vital during this period.

grass tetany