Once cool-season forages begin to reemerge in your grazing pastures, grass tetany can become a potential problem in grazing cattle. We typically see issues with grass tetany during the months of February, March and April. Cattle grazing the lush regrowth of spring grass or annual cereal forages, such as wheat, oats or rye, can experience a deficiency of magnesium leading to this problem. Magnesium is a critical nutrient for normal nerve and muscle function. Early signs in cows affected by tetany include a decreased appetite, frequent urination and separation from the herd. This would be followed by increased excitability, muscle spasms around the face and ears as well as a stiff or unsteady gait. These early signs may occur over a short two- to three-hour period, making early detection difficult. As the disease progresses, an affected cow will lose normal muscle control. This forces the affected animal to lie down and become unable to get up. If your cattle are not checked often, a dead cow may be the first sign of a problem.

Grass tetany is due to an abnormally low level of magnesium in the cow’s body, and lactating cows are more susceptible. Ruminant animals absorb magnesium from the intestinal tract much less efficiently than other species. Magnesium and calcium levels can also be low in a cow’s body due to losses in milk during lactation or due to an increase in a cow’s potassium intake. High potassium levels occur in young, rapidly growing forage and can be a problem in cool-season grasses such as fescue or in winter cereal grains. Tetany can also occur in cows being fed grass hay in a dry lot situation, particularly when the hay is low in calcium and magnesium and simultaneously high in potassium.

Other factors such as spring fertilizer application can also increase the potential for grass tetany to occur. Heavy fertilization Prevention is the key to controlling grass tetany. This can be achieved by dispensing a saltmineral supplement containing at least 10 percent magnesium that can be utilized daily. Successful prevention begins with providing 2 to 4 ounces of mineral supplement containing 10 percent magnesium oxide per animal per day. The supplement must be provided on a daily basis because the cow’s body has no ability to store reserves. Several mineral feeders should be made available if stocking rates are higher. Producers should remain vigilant this time of year to prevent tetany from becoming a problem in the herd.

For more information about grass tetany and general herd management, contact your county Extension office.grazing pastures especially with potassium (potash) in the late winter or early spring may further inhibit magnesium absorption for the cow. Weather is another influence for grass tetany. Cloudy conditions decrease the plant’s ability to utilize magnesium, making it even less available to grazing animals, so tetany may be more often observed on cloudy or rainy days.