Grass Tetany – Getting Ready to Put Your Cattle on Spring Pastures

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With the warmer days and hints of sunshine here and there, we can definitely say that spring is here! Pastures are getting green and lush, and we can get those mama cows off the hay and back onto pasture. During this rapid growth, are we as producers paying extra attention to our cows? If not, we should be. During phases of rapid growth, the forages in your pasture may not be able to take up nutrients from the soil at the rate that they need to in order to get enough nutrients into the cattle. Furthermore, high moisture content in the forage can cause it to move through the digestive system too quickly, and nutrients are not able to be absorbed. This puts them at risk of grass tetany.

Grass tetany is a deficiency of magnesium in the blood stream. Cattle are not very efficient at storing magnesium, as they can only store very small amounts in their bones and soft tissue. In addition to not being able to store magnesium very well, cattle lose magnesium easily through milk, urine, and digestive secretions. Considering that during the spring most cows have a calf at their side, this can lead to a ‘perfect storm,’ so to speak, when it comes to cows being affected by grass tetany. As producers, we have to keep in mind that even if intake of magnesium is low, loss of magnesium is going to stay the same.

Grass tetany can be managed, if the producer is diligent in caring for his/her stock. Unfortunately, in most cases, the first sign of grass tetany is a dead animal that seemed perfectly healthy the day before. This can be avoided by knowing what to look for before it is too late. When grass tetany is in its early stages, cows may give small warning signs such as twitching of the face and ears, or a stiff/abnormal gait. Moving into more advanced stages, the animal may become more aggressive or “wild” and nervous, may appear to be staring, or as I like to say, glazed over. The animals may also have an elevated rate of respiration and elevated heart rate. In the advanced stages, the cows will go down with muscle spasms and seizures. If untreated, the cow will die.

All of this information begs the question “what am I supposed to do about it?”

The best treatment for grass tetany is prevention. There are several management steps that a producer can take to minimize the chances of your cattle falling victim to grass tetany. Legumes tend to be higher in magnesium, so letting cattle graze on pastures with both grasses and legumes is one way to minimize the chances of your cattle being affected by grass tetany. Going forward, maybe think of adding in some clover in the years to come if grass tetany has been a problem for you in the past. Another good practice (which is also good advice for pasture health in general) is to wait to graze until the grass is AT LEAST 4 to 6 inches tall. Magnesium is even less available in the smaller, less mature plants. Feeding a magnesium supplement will aid in reducing risks of grass tetany as well. These supplements will continually keep blood magnesium levels in a target range to be used by the animal. Magnesium oxide is a great option for supplementation. Magnesium oxide tends to be unpalatable, so adding in something like molasses may be necessary to make it more appetizing to your cattle. The most commonly used prevention method in our area is a High-Mag minerals. Your feed company representative should be able to tell you what your options are for a high-mag mineral, and most all of the big-name brands have them available. You want these minerals to be 10-14% magnesium to be effective. It is important to remember that INTAKE IS KEY when supplementing magnesium. You can offer the best minerals, but if your cows don’t eat them, they won’t be effective. The amount of magnesium in your minerals will determine how much your cows need to consume every day.

Knowing your risk factors is essential to prevention as well.

  • Pastures that have recently been fertilized with nitrogen can increase the chances of grass tetany, as nitrogen can inhibit can magnesium uptake.
  • Cows that are high milk producers or are in peak lactation are at a higher risk because magnesium leaves the body by milk.
  • Lush pasture growth right after a rainy season can cause decreased levels of magnesium in the plant itself, as nutrient uptake cannot keep up with growth.
  • Stress to the cattle such as the stress of moving, wind and rain exposure, sudden changes in feed, and sudden lowering of temperature can decrease blood magnesium levels.
  • Older cows with young calves are at a higher risk.
  • Cool-season grasses such as fescue, and small grain forages like oats, rye, and triticale can put your animals at a higher risk of grass tetany.

When the need arises for treatment, the best treatment is to have a veterinarian administer intravenous calcium and magnesium solution. When timing is critical and action needs to be taken very soon, the producer can administer a calcium and magnesium supplement under the skin. Once this happens, the producer should follow up with mineral supplements to make sure that magnesium levels do not fall again.

The best way to combat grass tetany is to know the signs, know the risk factors, and know your animals. If you suspect grass tetany is affecting your cattle, work with your veterinarian to diagnose and treat those animals and remember, early action is the best action.

-Katelyn Stovall