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Grass Tetany

Causes of grass tetany and how to combat it.

Nashville, Ark. – Grass tetany in Arkansas normally occurs in February, March, and April. It is caused by an abnormally low level of magnesium in a cow’s body. This imbalance can be indirectly caused by heavy fertilization. A heavy potassium (potash) fertilizer application can decrease the dietary absorption of magnesium in the cow’s gastrointestinal system. Young and rapidly growing forages usually have an increased amount of potassium. Typically, this disease will occur in older lactating cows, but it can also be seen in cows with poor body condition scores or cows that are over-conditioned. A moist, cool spring and stress may also play a role in this disease. Symptoms may range from slight changes in behavior to death. Early in the disease, the affected cow may have a decreased appetite, decreased milk production, a tendency to stay away from the herd, increased alertness, or a stiff or unsteady gait. As the disease progresses, cattle may become recumbent or exhibit muscle tremors, an increased heart rate, and an increased breathing rate. If the disease is left untreated at this stage, the cow will likely die.

Magnesium Imbalance

Correcting the magnesium imbalance is the most important part of treating grass tetany. If the clinical signs are mild, magnesium can be corrected with approximately 150ml of a 20 percent magnesium sulfate solution. This must be given subcutaneously in several injection sites. If the clinical signs are more severe, a veterinarian should be involved.

How to Prevent Grass Tetany

Grass tetany can be prevented in a few different ways. You can limit the amount of time cattle grazes fresh pasture. Let them fill up on hay before turning them out to pasture. You may provide special high magnesium mineral blocks or loose minerals. They should have magnesium for two weeks before turning them out on fresh pastures to make sure their magnesium levels are adequate. Remove any other salt blocks from the pasture to make sure they are getting enough of the high magnesium minerals. You may mix loose magnesium minerals with molasses or ground corn to aid in consumption.

For more information on grass tetany, call the Howard County Extension Office at 870-845-7517 or view some helpful fact sheets on our website The Cooperative Extension Service is part of the University of Arkansas System Division of Agriculture.

By Dawson Bailey
County Extension Agent - Agriculture
The Cooperative Extension Service
U of A System Division of Agriculture

Media Contact: Dawson Bailey
County Extension Agent - Agriculture
U of A Division of Agriculture
Cooperative Extension Service
421 N. Main Nashville AR 71852
(870) 845-7517


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