Preventing Grass Tetany

By Cheryl Kepes

Strategies to keep cattle healthy on new, lush spring forage

Finally, green grass has erupted from the ground-filling pastures, producing a stage prime for spring grazing. It seems like the moment livestock producers have been waiting for has arrived. Yet, with the emergence of lush spring grass comes the possibility of grass tetany in cattle herds.

Causes: Livestock extension specialists point to diluted mineral contents in pastures, particularly low levels of magnesium (Mg), as the root cause of grass tetany in cattle. The reduced levels of magnesium in forages may occur for a variety of reasons, including poor soil conditions or nutrient relationships within the plant that result in a magnesium-deficient forage.

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Poor magnesium content in forages leads to magnesium deficiencies in some animals. The lack of adequate amounts of magnesium can cause grass tetany in cattle. Some animals are more susceptible to grass tetany than others. “Grass tetany is more prevalent in older cows, due to a reduced absorption of magnesium in the rumen, and in cows in early lactation,” Earl Ward, NE Area Livestock Specialist with Oklahoma State University Extension, said.

Older cows and cows nursing calves under the age of 4 months have a reduced ability to pull magnesium from their bones. Therefore, those sets of cows should be more closely monitored for signs of grass tetany.

Impact and Treatment: The initial signs of grass tetany, sometimes referred to as “grass staggers,” are salivation, excitability and an uncoordinated gait.

“Animals with grass tetany need to be handled extremely carefully because the more excited they get, the worse the condition gets,” Ward explained. “That’s why many of them go down in the chute.” Without intervention, grass tetany can progress to convulsions, coma, and death. If an animal dies due to grass tetany, typically, there will be signs of thrashing near its body.

If caught during its early stages, animals with grass tetany can be treated. Producers should remove the sick animal from the pasture and increase the magnesium in its blood through injections. Livestock extension experts state the USDA recommends injecting subcutaneously a 200 ml dose of a 50 percent solution of magnesium sulfate.

“Another method is to give an intravenous injection of calcium-magnesium gluconate,” Ward added. “However, this injection requires the animal to be calm and preferably sedated because it must be given slowly to avoid putting the animal into cardiac arrest.”

Prevention: Grass tetany can be prevented through several management practices. One way to decrease the chance of grass tetany is waiting until the forage is more mature before allowing cattle to graze it. When grasses reach 6 inches of growth the forages contain higher magnesium levels. Though for many producers this is an unlikely strategy due to the pressing need for grazing pasture for their animals.

Therefore, a more viable prevention measure is providing a magnesium supplement for the herd. Livestock specialists recommend mixing Magnesium oxide (MgO) with salt and feeding it at a 75 percent salt to 25 percent magnesium oxide ratio. Additionally, there are commercial minerals that contain a “high” magnesium content to help the cow herd increase its magnesium intake. Another option is providing additional magnesium through the water supply. However, magnesium oxide is insoluble in water. Other alternates are magnesium acetate, magnesium chloride and magnesium sulfate which are all soluble options that can be used in the water supply.

If the problem stems from improper mineral levels in the soil, then a soil test can reveal what nutrients are lacking. With that information in hand, producers can then take steps to manage for low magnesium.