EXTENDING OUR REACH: The what, when and why of Grass Tetany

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Michelle South

Grass Tetany, or Hypomagnesemic Tetany, is the lack of adequate magnesium in the blood of animals. This low concentration of plasma magnesium leads to muscle spasms, convulsions (seizures), respiratory distress, collapse and eventually death. This dietary requirement of absorbed magnesium is stored and utilized in the animal’s bones and muscles for movement and lactation. 

Grass Tetany occurs when the magnesium requirement for these actions is not met. Animals consistently lose magnesium through their urine, feces and milk. To make up for this loss, animals demand a daily ingestion requirement. When animals are grazed on lush green pastures low in magnesium, Grass Tetany is likely to occur. Pastures in mountainous areas are considered high-risk due to the frequent swings in temperature making grass grow in short spurts. Also, it can happen when high levels of potassium and nitrogen are ingested, such as when fields have been recently fertilized with nitrogen or potassium fertilizers.

Grass Tetany can affect any animal, but most commonly, it is seen in adult lactating small or large ruminant animals (cattle, goats and sheep). 

Animals affected by Grass Tetany may appear to be grazing normally but will suddenly begin to bellow and gallop around the field blindly. Then animals will start seizure-like activity. Death usually follows within a few hours after convulsions start. In most instances, producers will find animals dead in the field with no knowledge of any previous sickness.

Treatment of Grass Tetany includes a licensed veterinarian giving combined solutions of the proper amounts of calcium and magnesium. A daily oral supplement of magnesium oxide can be offered and is highly suggested during the danger periods (early spring). Most commonly, this comes in the form of a “high mag” (high magnesium) loose mineral that is given through free choice. It is suggested producers provide an unlimited amount of quality hay with the mineral for proper digestion. 


Call Area Agent, Agriculture-Livestock Michelle South at the Mitchell County Cooperative Extension Center at 828-688-4811 or email mcsouth@ncsu.edu with questions or concerns about your animals or pasture. Call your local veterinarian immediately and seek treatment if an animal is presenting signs of Grass Tetany.