top of page

5 Things to Know About Grass Tetany

5 Things to Know About Grass Tetany

Everything comes to life in the spring. Crops are being planted, flowers are blooming and your livestock are ready to head to pasture. But is the grass ready? Should I be worried about grass tetany?

What is Grass Tetany?

Grass tetany is caused by low levels of magnesium in the blood of cattle. More common in the spring, grass tetany occurs when cattle begin grazing on lush, immature grasses that are high in potassium.

High levels of potassium decrease the absorption of magnesium, causing decreased magnesium levels. Ensuring cattle have highly available forms of magnesium in the spring is critical for the prevention of grass tetany.

To help your cattle keep their nutrient intake focused on growth and gain, here are five things you need to know about grass tetany.

5 Things to Know about Grass Tetany

1. Cool-season grasses are most likely to cause grass tetany.

Cool-season grasses, such as crested wheat grass, bromegrass, bluegrass and timothy grasses are the most likely to have high levels of potassium and cause grass tetany in the spring. Cereal grasses such as wheat grass, rye and oats can also be a culprit of tetany. According to the United States Department of Agriculture, wheat pasture poisoning is a form of tetany typically experienced when cattle graze on early winter wheat pastures, particularly in the Texas and Oklahoma panhandle area. While often thought of as a magnesium deficiency, wheat pasture poisoning is a calcium deficiency. Wheat grasses with high levels of potassium can also interfere with calcium absorption in cattle.

Pastures fertilized with nitrogen and potassium can also increase the risk of grass tetany. Excess nitrogen and potassium to the plant further decrease the availability of magnesium to the animal.

It's recommended by North Dakota State University to wait until grasses are 8-10 inches tall before turning cattle out to pasture. As grasses grow the levels of potassium will wane and magnesium will become more available, reducing the risk of grass tetany.

2. Grass tetany is more common in lactating cows.

Grass tetany is more common in older lactating cows or cows in late gestation grazing on lush spring forages. Cows have limited reserves of magnesium in their body to start with. Adding extra demand on the cow during lactation and gestation puts them at a further magnesium nutrient deficit. Lactating cows and cows in late gestation should be frequently monitored and provided a high magnesium mineral to help prevent incidences of grass tetany.

3. Grass tetany can be fatal.

Grass tetany can develop rapidly, with the first symptom often being a dead animal. Other symptoms to look out for are excitability, lack of coordination, muscle twitching, convulsions, comas and excess salivation.

Weather can also play a factor in grass tetany. On cool, cloudy days between 40-60 degrees Fahrenheit, more instances of grass tetany and its symptoms typically occur.

4. Salt can play a role in grass tetany prevention.

According to research conducted by British scientists in the 1930s, salt can also help prevent grass tetany.

Magnesium absorption in the rumen is dependent on sodium. Forages contain sodium, but a spring freeze or frost can result in the drying of young forages, making them sodium deficient. It’s recommended that free choice salt be included on every pasture in the spring. Providing salt blocks alone will not be enough. Cattle cannot consume the required amount of salt from a block.

Mineral containing high salt content and highly available trace minerals like magnesium is also recommended.

5. Treat grass tetany with an IV injection of magnesium-calcium. Prevent grass tetany with high-quality mineral.

If grass tetany is suspected, immediately consult with your veterinarian. Typical grass tetany treatment includes an IV injection of magnesium-calcium and a mineral supplement containing a high level of magnesium (10%) and calcium between (15-20%). For prevention, mineral containing highly available magnesium, calcium and salt should be provided with daily intake ranging from 2-4 ounces.

Even if you test the magnesium levels of your forages before spring and it’s at adequate levels, it’s still recommended to provide a mineral supplement. The magnesium in the forage is not always available to the cow.

Before cows go to spring grass, increase the magnesium and calcium in your mineral. This should be done as early as February or March, so cattle can begin to store mineral reserves in their bones.

To learn more about grass tetany prevention and what minerals can help, contact ruminant specialist Dr. Jeff Hill at 507-337-6916 or email

bottom of page