Grass tetany may also be referred to as grass staggers, wheat pasture poisoning, magnesium tetany and hypo magnesia. It most often occurs when cattle are grazing lush, immature grass during cool and cloudy weather. These lush grasses are high in potassium and low in calcium and sodium. It is most prevalent in older, high-milk producing cows during peak lactation, but also may affect young cows and growing calves. Milk contains high levels of magnesium and that is why high-milking cows tend to be more susceptible. Cattle grazing nitrogen fertilized grass pastures, high in potassium, are also more susceptible to grass tetany due to greater forage potassium levels interfering with magnesium uptake.
Sometimes clinical signs are not observed and you may just find a dead animal. Affected animals may exhibit the following: become excitable, exhibit a “wild” stare with erect ears, appear to be blinded, become uncoordinated, tend to lean backward, stumble and go down, frequently urinate and may walk with stiff legs.
Prevention is the best management strategy. Magnesium is not stored in the body and therefore needs daily supplementation. A “High-Mag” commercial mineral mix with 8-10% magnesium should be successful in prevention. However, it is important to begin supplementation before the grass tetany season begins and to continue until the threat has passed. Pastures with 30-40% legumes will provide increased forage magnesium and calcium while reducing nitrogen fertilizer needs. Just another benefit of adding legumes to pastures.
Shawn Deering is a livestock specialist for Mu Extension in Gentry County.