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Updated: Jul 21, 2020

Well the rains have finally come and in many areas the grass is starting to grow. Everyone is sick of hand feeding animals and is racing to get enough grass to start animals grazing. Lush, fast growing grass and cereal crops unfortunately provide an ideal forage source for animals to be affected by grass tetany.

Grass tetany occurs when an animal’s magnesium intake/absorption drops below the animal’s critical needs, otherwise known as hypomagnesemia. As the majority of magnesium is stored in the animal’s skeleton it is hard for them to quickly access, especially in older animals. Ruminant animals absorb magnesium through the rumen wall and this can be affected by rate of passage in the rumen and levels of potassium in the diet.

Signs of cows that are affected by low magnesium can be that they are aggressive in nature and show signs of muscle tremors and in some cases, it can lead to death. The condition progresses quickly and therefore many animals are just found dead.

Older animals (over five years) are at the greatest risk, as are animals that are on fast growing pasture or crop that have had high levels of nitrogen or potassium fertilisers applied.

Perennial ryegrass toxicity PRGT can sometimes be mistaken for grass tetany as animals in both cases have muscle tremors and difficulty standing. They are both vastly different issues with PRGT coming from toxins in the ryegrass that act as the plants defence system, whereas grass tetany as previously described occurs from low blood magnesium.

Best practice based on current knowledge is to provide the animals with a high magnesium supplement, some people try to dust pasture or hay with magnesium, but this is labour restrictive. Using a high-quality loose lick mineral, with a high magnesium content will allow animals daily access to meet their nutritional requirements. Feeding high risk cattle hay will slow the rate of rumen passage down allowing the animal to absorb more magnesium out of the feed stuff.

To help manage this year’s Grass tetany season

  • Graze grass at 2.5 plus leaf stage as the plant will have more fibre and less potassium

  • Minimise sudden changes in diet - if your cows are in confinement make the change to pasture over 10 - 14 days to allow the animals digestive system time to adapt

  • Reduce stress events like yarding or long-distance movements

  • Provide your animals with a high-quality loose lick with added magnesium like the ones from the TPM range

For more information on how to aid in the prevention of grass tetany & ryegrass staggers in your herd, contact your local TRAC Expert.


Our Consultants


Mark Facy

0437 243 320

Owen Rees

0429 437 823

Mikaela Baker

0457 243 319


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