Grass tetany is most often associated with cattle grazing immature cool-season grasses or lush annual forages. However, it can also occur during the winter when cattle are fed hay. This condition can happen with regular hay, alfalfa hay, or annual forages that have been harvested for hay. It is especially true if hay is being fed in a dry lot, which is the only feed source.
For those of you not in the know, you may be asking, “What is grass tetany?“, “What kinds of problems can it cause my operation?” and “How do I treat or even prevent it from happening?“. Regarding those questions, here are some things you should consider.
What is grass tetany?
Grass tetany is a metabolic condition in cattle that occurs when there isn’t enough Magnesium in their bloodstream. Magnesium is crucial for proper muscle and nerve function. When levels drop too low, cows can start showing symptoms that range from irritability and muscle twitching to staggering and, in severe cases, even death. Many people associate grass tetany with spring grazing. Still, it can happen in winter, too, if cattle eat hay or silage low in Magnesium.
This condition is most common when cows graze on fast-growing, lush grass in the spring or when fed particular hay or silage. These types of feed can sometimes lack sufficient Magnesium, especially if they’re also high in potassium, which interferes with magnesium absorption. Older cows and those in late pregnancy or lactation are especially prone to grass tetany, as their bodies have higher mineral demands that can be hard to meet without extra supplementation.
Preventing grass tetany starts with understanding your feed. Testing hay for mineral levels can help you catch low Magnesium before it becomes an issue. If your hay or pasture is low in Magnesium, consider supplementing with a high-magnesium mineral mix or using magnesium lick blocks. It may seem like extra work, but a little prevention can go a long way in keeping your cattle healthy and your operation running smoothly.
What causes grass tetany?
Grass tetany is a metabolic disorder caused by a low blood concentration of the mineral Magnesium. It can be found in all classes of cattle and can be fatal if not treated in time. Magnesium is critical to the nervous system and muscle function.
Grass, alfalfa, and cereal grains harvested for hay can be low in Magnesium. Hay is considered low if the mineral analysis shows less than 0.15% magnesium in the hay. When it is low in Magnesium and calcium, less than 0.4%, and high in potassium, more significant than 2.5%, tetany is more likely to occur. This ratio differentiation can be a problem during dry years, as we typically experience.
Forages that are likely to cause grass tetany are typically borderline low in Magnesium but have high potassium levels. Also, those forages will tend to be lacking in sodium. High potassium levels will interfere with the absorption of Magnesium. It is the excess potassium that causes tetany. An imbalance of potassium, calcium, and phosphorus in feed can negatively affect the absorption of Magnesium from digestion to the bloodstream. This imbalance can magnify your problems.
The production stage can also determine whether a cow is at risk of grass tetany. Cows in the late gestation and lactation stages can get it because their bodies use the Magnesium they consume for milk production.
Some forages are riskier than others.
Some forages are riskier than others regarding grass tetany because of their mineral balance, especially their Magnesium, calcium, and potassium levels. Fast-growing, lush grasses, particularly cool-season ones, often lack enough Magnesium and calcium to meet a cow’s needs. This low mineral content becomes problematic when potassium levels are high, as potassium interferes with how well cattle can absorb Magnesium, increasing the risk of tetany.
Certain types of hay, like alfalfa or hay harvested from cereal grains, can also put cattle at risk if they have low Magnesium and calcium content. Hay grown during dry years, when mineral levels in the soil might be lower, can be especially risky. When this hay is the only feed source, particularly in a dry lot where there’s no grazing variety, cows can develop mineral imbalances, making tetany more likely.
Older cows and those in late pregnancy or lactation stages are more at risk with these low-magnesium forages since they need extra minerals. Unlike younger cows, older cows don’t pull as much Magnesium from their bones, so they rely heavily on their feed to meet this need. Choosing the suitable forage and supplementing when needed can help balance their diet and reduce the risks associated with grass tetany.
Symptoms
Diagnosing the symptoms of grass tetany visually can be a little tricky. The symptoms can come on so fast that by the time you see them, the cow could already be dead.
Some of the symptoms can include grazing away from the herd, increased irritability, muscle twitching, convulsions, decreased milk production, and even a staggering walk. Unless you are watching your herd very closely, it can be challenging to see the early signs of grass tetany.
If left untreated, cows will then lie down and begin a paddling-like motion with their legs. The final stages of the symptoms are that the cow will lie down, slip into a coma, and then die.
Ways to treat it
It can be challenging to treat grass tetany quickly because the cow’s death can occur relatively quickly. One day, the cow may look fine, but then the next, she will be dead.
If your herd has grass tetany, you will need to restore magnesium levels in its blood. Preventing it from worsening requires immediate action, and there are a few different ways to do that.
Veterinary professionals can inject the cow with Magnesium and Calcium solutions intravenously. This injection can work during the early stages of the disease when time is not as critical as later on.
Suppose it is a severe problem, and you must act relatively quickly. In that case, the producer can inject the Magnesium/Calcium solution under the skin.
There are also some oral options that are available to the producer. These options are generally to prevent any of your cows from relapsing. These oral sources of Magnesium are:
- A Magnesium oxide powder for putting onto either feed or on the pasture
- Magnesium lick blocks
- Slow-release capsules
- Magnesium sulfate or soluble magnesium chloride that can be added to hay or silage
- Adding Magnesium to concentrates
You can purchase these products at your local feed store or from your veterinarian.
Ways to prevent grass tetany
Tetany prevention is more critical since it is difficult to treat or even correctly diagnose. This process begins with testing your hay. Testing will tell you if there are any imbalances in Magnesium, potassium, and calcium. I go over how to test your hay in a previous post, “Hay sampling: what to know.”
If the hay tests low in Magnesium, less than 0.15%, and calcium, less than 0,4%, while also being high in potassium, more than 2.5%, consider using a supplement. It would be best to use a high calcium, high magnesium supplement that contains 10-13% Mg for a 4oz target intake with salt.
If you choose that option, remember that magnesium oxide has a bitter taste. To make it more palatable, you can mix it. Use either dried distiller’s grains or soybean meal at 1lb to 50 lbs of the mineral salt mix. This mixture will help increase intake if your consumption could be better. If you are hand-feeding protein or energy, you can deliver the magnesium supplement with it.
Another thing to think about when having hay that is high in potassium and low in Magnesium is mixing it with other hay. Much like dealing with one’s high nitrates, you can “water down” the problem of hay by combining it with hay that is higher in Magnesium and calcium. Alfalfa can also be high in potassium, so be sure to test it before feeding.
If you are looking for other ways to treat tetany, then check out some articles by the University of Nebraska at Lincoln.
Step by Step prevention plan
This prevention plan covers essential steps to avoid grass tetany. It ensures that cattle stay healthy by maintaining the proper mineral balance, mainly when natural forage and hay conditions may not be optimal.
Step 1: Test Forages
- Start by testing your hay and any other feed to identify mineral levels, specifically Magnesium, calcium, and potassium. Ideal forage should contain at least 0.15% magnesium and 0.4% calcium, with potassium under 2.5%. Testing early helps you know if supplements are necessary to meet these needs.
- Suppose your hay is low in Magnesium and high in potassium. In that case, it’s a good candidate for supplementation or mixing with other types of hay.
Step 2: Supplement with Magnesium-Rich Minerals
- Provide a high-calcium, high-magnesium supplement with about 10-13% magnesium for a target intake of 4 ounces per cow daily. Look for a mineral mix specifically formulated for magnesium deficiency to ensure cows get what they need.
- Mix magnesium supplements with feed or use a carrier like dried distiller’s grains to make them more palatable. If you’re hand-feeding, consider feeding the supplement with protein or energy sources for additional intake encouragement.
Step 3: Provide Magnesium in Multiple Forms
- Offer magnesium in various forms, like lick blocks, magnesium oxide powder sprinkled on feed, or slow-release magnesium capsules if suitable. Having a variety of options increases the chances of your cattle consistently taking in enough Magnesium.
- Magnesium sulfate or chloride can also be added to silage or hay, which helps prevent deficiency without changing daily feed habits.
Step 4: Use Mixed Hay to Balance Feed
- If you have high-potassium hay, blend it with a magnesium-rich or low-potassium forage. This “watering down” effect reduces the risk of tetany and keeps the potassium level from overwhelming magnesium absorption.
- Avoid using alfalfa as a primary mix unless it’s been tested, as it can sometimes be high in potassium, which could counteract the benefits.
Step 5: Monitor Cows Closely During Risky Seasons
- Pay extra attention to cattle in early spring or during winter when they’re consuming mainly hay. Cows in late gestation or lactation and older animals are especially at risk, so watch for signs like restlessness, muscle twitching, or isolation from the herd.
- Ensure at-risk animals have regular access to supplements and avoid overcrowding in dry lots, where competition for feed can affect intake.
Step 6: Keep Emergency Treatment on Hand
- If possible, have magnesium/calcium injectable solutions on hand or work with a veterinarian who can respond quickly in an emergency. Early intervention is key, so having a plan for quick treatment can save lives if symptoms arise.
- Oral supplements are also helpful to prevent relapses in cows that have recovered from tetany.