Magnesium Deficiency – Grass Tetany

Cattle store very little magnesium in their body and rely on Magnesium being supplied daily in their feed. If pasture levels are low this can trigger a deficiency.

Symptoms include:

  • Sudden deaths.
  • Early signs…facial & ear twitching.
  • Become agitated with sounds or movement eg Handling, birds flying overhead.
  • Staggering as it becomes worse.
  • Lying on side with convulsions, muscle spasms, thrashing.


A veterinarian will inject animals but if symptoms are recurring farmers may need to do so themselves, as cattle die quickly once on the ground.


  • Pasture flush after good rains/Spring pastures.
  • Any reduction in feed intake e.g. handling, yarding, bad weather.
  • Pastures fertilized with high nitrogen or potash.
  • Lush winter pastures e.g. rye & oats.
  • Cows in early lactation.


  • Riverina dairy feeds contain extra Magnesium in the winter months which works on most farms.
  • If an outbreak occurs additional magnesium can be added to your dairy or beef feed.
  • Contact your sales representative or nutritionist for advice on levels.