Grass Tetany is caused by an acute Magnesium (Mg) deficiency which often occurs from grazing lush swards that are low in fibre.  Cows are at higher risk of tetany during cold, wet weather and stress such as weaning can also increase the chances of the disease.

Cows do not have the ability to store much Mg in their bodies hence they need a daily supply from their diet, If intake is low then a deficiency can occur very quickly, leading to death in many cases.


More often than not, unfortunately the first sign of tetany in a cow is to find them dead, but common symptoms are:

  • Frothing at the Mouth
  • Staggers
  • Body Tremors
  • Hyper Behaviour

If a cow is identified with tetany like symptoms immediate veterinary intervention is needed to administer a Magnesium Sulphate solution.

Prevention is Better than Cure

Most certainly with grass tetany prevention is better than cure and there are many ways farmers can reduce the risk of grass tetany.  Methods of prevention are based around providing a regular daily intake of magnesium during high risk periods.

A combination of the methods below can be used to increase Mg intake:

  • Magnesium blocks/Licks
  • Magnesium Bolus
  • Daily feeding of high Mg concentrates
  • Buffer feeding with hay or straw
  • Adding Mg to the drinking water
  • Pasture dusting with calcined magnesite

For further advice on any of the above, please contact a member of the Moocall team to speak to some of our breeding specialists on +353 1 96 96 038 or email