Grass tetany, caused by magnesium deficiency, typically occurs in beef cows during early lactation and is more prevalent in older cows. Grass tetany most frequently occurs when cattle are grazing lush immature grasses or small grains pastures and tends to be more prevalent during periods of cloudy weather. Symptoms include incoordination, salivation, excitability (aggressive behavior towards humans) and, in final stages, tetany, convulsions and death.
When conditions for occurrence of tetany are suspected, cows should be provided mineral mixes containing 12% to 15% magnesium and be consumed at 3 to 4 ounces per day. It is best for the supplements to be started a couple of months ahead of the period of tetany danger so that proper intake can be established. Because tetany can also occur when calcium is low, calcium supplementation should also be included, according to Glenn Selk, Oklahoma State University emeritus Extension animal scientist.
Click here to learn more about mineral nutrition of grazing cattle.