Management practices to overcome the incidence of grass tetany.

ABSTRACT

To minimize the incidence of grass tetany, winter pastures should be established on soils containing Mg-rich minerals, drainage should be improved on five-textured soils, legumes should be included in the sward and soil pH should be at least 5.5. Liming acid soils with dolomitic lime increases forage Mg by supplying Mg and by raising soil pH. Calcitic lime applications also can increase Mg availability to plants on soils with adequate Mg. Low rates of application of soluble Mg salts (less than 100 kg/ha of Mg) effectively increase Mg uptake from noncalcareous soils with low cation exchange capacity. Potassium levels in soils and plants should be kept in the lower range of recommended values. Nitrogen application should be regulated to provide the desired level of forage production. Nitrogen fertilizers, especially the nitrate form, stimulate plant Mg uptake if Mg is available in the soil. The most practical and cost-efficient method of supplementing dietary Mg intake is to provide free-choice Mg. Supplements must be palatable and placed in locations frequently used by cow herds. Including a high-energy feed in the supplement may at times increase its preventive effectiveness by increasing Mg absorption and reducing lipolysis. Regardless of the supplement formulation, Mg intake should be monitored on a regular basis, and formulation or management changes should be initiated if Mg consumption is below required levels. In severe grass tetany outbreaks, foliar application of Mg or administration of Mg via the drinking water may be warranted.