Spring weather might feel like a distant dream right now, but it’s just around the corner. Before long, the ice and snow will melt away (if you get any), and your pastures will come alive with lush green forages. This seasonal shift is a welcome sight for many, signaling new growth and fresh grazing opportunities for your herd. But lurking behind all that greenery is a hidden danger. This silent threat can strike quickly and severely impact your cows’ health and production. This threat is called grass tetany.
As winter fades and spring takes over, the moisture left behind combines with rising temperatures to kickstart your grasses into their “Spring Greenup.” It’s an exciting time when dormant pastures burst into rapid growth, painting your fields in vibrant shades of green. While this transformation may seem like a farmer’s dream come true, it’s not without its risks. This rapid growth brings unique challenges, and one of the most concerning is the risk of grass tetany. This condition can wreak havoc on your herd if you’re not prepared.
If you’ve never heard of grass tetany, you might wonder, “What exactly is it?” “How could it affect my operation?” and most importantly, “What can I do to prevent it?” These are essential questions every cattle producer should ask. Grass tetany is a metabolic disorder linked to low magnesium levels in your cows’ blood, often triggered by grazing on lush, rapidly growing pastures. To help you understand the risks and solutions, let’s break it down so you can keep your herd safe this spring.
What You Need to Know About Grass Tetany
Grass tetany is a metabolic disorder that is caused by a low concentration of the mineral Magnesium in the blood. A producer can find it in all classes of cattle, and if it is not treated in time, it can be fatal.
This disease typically occurs when cows graze rapidly growing, lush, green pastures. It can also occur when cows graze cereal grains, but it tends to happen more often during the spring with warm-season grasses.
During their early spring growth, forages are low in many minerals, including Magnesium. At this time, forages do not absorb enough Magnesium from the soil. This problem is compounded by the fact that forages are mostly water at this stage. This problem means cows cannot consume enough of it to get the necessary minerals.
The risk of grass tetany also increases in lush, green pastures that are high in Potassium and Nitrogen. These particular minerals can interfere with the cow’s absorption of Magnesium.
The cow’s production stage can also influence whether or not she will get grass tetany. Cows in the late gestation and lactation stages can get it because their bodies use the Magnesium they consume for milk production.
Older cows tend to be more likely to get it than their young counterparts. This reason is because the older ones are not able to pull Magnesium from places like their bones to meet their bodies’ demand for it.
How to Recognize Grass Tetany
Recognizing the symptoms of grass tetany in your herd is a proactive step that can make you feel in control. This metabolic disorder can strike so quickly that by the time symptoms are visible, it’s often too late to intervene. That’s why being proactive and vigilant is critical. Early detection can be tricky because the signs may start subtly, making them easy to miss unless you monitor your cows closely.
The early symptoms of grass tetany can include unusual behaviors like grazing away from the herd, increased irritability, and restlessness. You might also notice physical signs such as muscle twitching, a staggering walk, or even convulsions. These symptoms occur because Magnesium, which plays a vital role in neuromuscular function, is lacking in the cow’s system. Another red flag is decreased milk production, which can directly impact your operation’s profitability. While these symptoms may seem manageable initially, they can escalate rapidly.
If grass tetany is left untreated, the condition worsens quickly. Affected cows may collapse and exhibit a paddling motion with their legs—a distressing sign that the disease is advancing. In its final stages, the cow will slip into a coma and, ultimately, succumb to the disorder. This rapid progression highlights the urgency of acting swiftly and being prepared to address the issue before it spirals out of control. Knowing these signs and staying alert can make all the difference in protecting your herd.
Treatment Options: Acting Fast When It Counts
It can be difficult to treat grass tetany quickly. This is 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 must restore the magnesium levels in its blood to prevent it from getting worse. There are a few different ways to do that.
One way to do this is for a veterinarian to give the cow an intravenous injection of Magnesium and Calcium solution. 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 quickly. In that case, a producer can inject the Magnesium/Calcium solution under the skin. However, if you are not entirely used to this, I would not recommend doing this yourself.
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
Your veterinarian or local feed store can provide you with these products.
Preventing Grass Tetany: Tips for a Healthy Herd
Grass tetany is one of those conditions where prevention truly is better than cure, mainly because treating it can be so difficult and often comes too late. One of the most effective ways to reduce the risk is by offering high-magnesium supplements. Mineral tubs containing 8–12% magnesium are an excellent choice, but there’s a catch—Magnesium isn’t very appealing to cows. To encourage them to consume enough, you can mix it with salt or other palatable feeds. Start providing these supplements at least 30 days before spring green-up to ensure your herd has adequate magnesium levels before the risk period begins. This proactive approach can make you feel responsible and in control of your herd’s health.
Another key prevention strategy is managing the quality of your forage. While lush green pastures may seem like the perfect source of nutrition, they can sometimes work against your cows. High levels of potassium and nitrogen in the soil can interfere with magnesium absorption, making grass tetany more likely. To avoid this, test your pastures and adjust your fertilizer program as needed. Reducing excessive potassium and nitrogen applications can go a long way in ensuring your cows can absorb the Magnesium they need from their diet.
Roughages can play a role.
In addition to mineral supplementation and forage management, it’s crucial to boost roughage intake during the early spring. At this time of year, the new growth in pastures is often high in moisture and low in fiber, which can throw off your cows’ nutrient balance. Providing additional hay or other forms of roughage helps to fill this gap and support proper digestion. This extra roughage also slows down the rapid intake of high-moisture grass, giving your cows a better chance to absorb essential nutrients, including Magnesium.
The bottom line is that a little preparation can save you from big problems later. Grass tetany strikes fast, leaving little to no time for treatment, so prevention is your best defense. You can significantly lower the risk of this deadly condition by combining high-magnesium supplements, careful forage management, and increased roughage in your cows’ diets. As the old saying goes, “An ounce of prevention is worth a pound of cure”—and with grass tetany, that couldn’t be more true.
Issue with Magnesium
An issue with increasing the amount of Magnesium offered to cattle is that the cattle will not consume enough to be of any help. This problem is caused by the fact that Magnesium is relatively low in palatability, so cows are less likely to eat it. Because it is so unpalatable, it is recommended to only put a high-Mg mineral in it when they need it. Another way to make it more likely to be consumed is to mix the mineral with a more palatable feed or salt. Adding salt will also mean the sodium requirement is being met, which will help with Magnesium absorption.
If you would like to read more about the importance minerals play in your cow’s diet, check out one of my previous posts, “What you don’t know about minerals can hurt.”
Now, let’s move on to when you should put the minerals out. According to the Veterinary Quarterly Review published by the Texas AgriLife Extension service, you should provide the supplement 30 days before grass tetany typically occurs, which means either in late winter or early spring.
During this time, your forages are mostly water. Increasing your cows’ roughage and energy intake is a good idea. Forages will be nearly 75% water at this time, which will dilute any nutrients they may provide
Another tactic you could use is reducing your forage’s Potassium and Nitrogen levels. Though these are also necessary nutrients, too much of them can negatively impact Magnesium absorption. Test your forages to find out what these levels are.
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