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5 Things to Know About Grass Tetany in Cattle


5 Things to Know About Grass Tetany in Cattle

As spring emerges, nature comes alive – fields paint green, flowers bloom, and our cattle eagerly await grazing. But as we revel in the season's energy, a question arises: Could our cattle face the risk of grass tetany? Let's unpack this springtime concern so you can avoid it!


What is Grass Tetany in Cattle?

Grass tetany, a condition caused by low magnesium levels in cattle’s blood, is more prevalent in the spring. This occurs when cattle start grazing on young, lush grasses that are rich in potassium.


High levels of potassium hinder magnesium absorption, leading to a decrease in magnesium levels. This is why it is crucial to ensure that cattle have easily accessible forms of magnesium during the spring to prevent grass tetany.

5 Must-Know Facts about Grass Tetany in Cattle

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

Certain grasses can seriously threaten your cattle’s health in the spring. Cool-season grasses like crested wheatgrass, bromegrass, bluegrass and timothy grasses are notorious for their high potassium levels, which can lead to grass tetany.


But it’s not just these grasses you need to watch out for – cereal grasses like wheat grass, rye, and oats can also contribute to tetany. In the winter, wheat pasture poisoning is a form of tetany that mostly affects cattle in Texas and Oklahoma. Wheat pasture poisoning is caused not just by a lack of magnesium, but also by a shortage of calcium. Wheat grasses with high potassium can also disrupt calcium absorption.


Pastures fertilized with nitrogen and potassium can also increase the risk of grass tetany. That’s right, the nutrients we often provide to support healthy pasture growth can hinder magnesium absorption in cattle.


To minimize the risk of grass tetany, experts recommend waiting until grasses reach a height of 8-10 inches before allowing your cattle to graze. As grasses grow, the potassium levels will decrease, while magnesium becomes more readily available. It’s a simple yet effective way to protect your livestock from grass tetany.


2. Grass tetany is more common in lactating cows.

Grass tetany is more common, especially in older lactating cows or those in late gestation grazing on lush spring forages. These cows already have limited magnesium reserves in their bodies. And when you add the extra strain of lactation and gestation, it only worsens the 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 is a silent killer that strikes suddenly, with the first symptom often being a dead animal. Other common symptoms that can occur include excitability, lack of coordination, muscle twitching, convulsions, comas and excessive salivation.


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


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

Discoveries made by British scientists in the 1930s revealed that salt has the potential to prevent grass tetany.


The absorption of magnesium in the rumen relies on sodium. While forages naturally contain sodium, a sudden freeze or frost can lead to the drying out of young forages, resulting in a sodium deficiency. To combat this, offering free choice salt on every pasture during the spring is highly recommended.


However, it should be noted that simply providing salt blocks isn’t enough, as cattle won’t receive the necessary amount of salt from a block alone. Mineral containing high salt content and highly available trace minerals like magnesium are the best options to prevent tetany.


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. Treatment of grass tetany typically involves an IV injection of magnesium-calcium and a mineral supplement with high levels of magnesium (10%) and calcium (15-20%).


To prevent grass tetany, offer a mineral supplement with highly available magnesium, calcium and salt. Aim for daily intake of 2-4 ounces.


Remember that even if your forages have adequate magnesium levels, providing a mineral supplement is still recommended. The magnesium in forage may not always be available to cows.


The bottom line is that before you turn your cows out to spring grass, increase their mineral magnesium and calcium levels to prevent grass tetany. Start early in February or March to allow cattle to store mineral reserves in their bones.


To learn more about grass tetany and what mineral is best for your herd, give us a call at 507-337-6916 or email RuminantHelp@RalcoAgriculture.com!

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