Controlling Grass Tetany

FAYETTEVILLE, ARK.
   Grass tetany can become a problem during the months of February, March and April. This disease normally occurs in Arkansas when our cool-season forages begin to regrow in late winter and early spring. Grass tetany is due to an abnormally low level of magnesium in the cow’s body, and older lactating cows are more susceptible.
   Early signs in cows affected by tetany include a decreased appetite, frequent urination, separation from the herd, increased excitability, muscle spasms and a stiff or unsteady gait. These early signs may occur for as little as two to three hours, 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 it becomes unable to get up. If your cattle are not checked often, a dead cow may be the first sign of a problem.
   Ruminant animals absorb magnesium from the intestinal tract much less efficiently than other species. Magnesium levels can also be low in a cow’s body due to magnesium losses in the milk during lactation or due to an increase in the 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 annual cereal grains like wheat and oats.
   Grass tetany is often directly related to influences such as rapid growth and heavy lactation in spring-calving cows. However, other factors such as spring fertilizer application can also increase the potential for grass tetany to occur. Heavy fertilization of grazing pastures, especially with potassium (pot ash) in the late winter or early spring, may further inhibit magnesium absorption in a cow’s intestinal system.
   Weather is another influence on the occurrence of 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.
   Prevention is the key to controlling grass tetany. This can be achieved by dispending a salt-mineral 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 up reserves. Several mineral feeders should be made available if stocking rates are higher for the herd. Δ
   DR. JEREMY POWELL: Associate Professor/ Animal Science, University of Arkansas