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.

Nutrition and Health of Dairy Animals

“…Clinical signs usually occur when the animal is both hypomagnesaemic and hypocalcaemic (Robinson et al, 1989). In its subclinical form, however, hypomagnesaemia may be risk factor for other diseases.…”

“…Ewes with twins are more susceptible to grass tetany than are ewes with single lamb (Mayland, 1988). Specifically, older lactating animals consuming lush, intensively fertilized, cool-season grasses during the early spring are the most frequently affected (Robinson et al, 1989). Older animals also have reduced ability to mobilize body reserves of Mg. Lower average environmental temperatures (<14°C) facilitate the onset of the disorder (Mayland, 1988).…”

“…The Mg concentrations in forage and subsequently in the blood of cattle are influenced strongly by high amounts of fertilizer K and, to some extent, fertilizer N. Absorption of Mg by plants is reduced by high levels of K in the soil (Mayland, 1988;Robinson et al, 1989). Mg absorption by ruminants is also reduced by a high intake of K (Schonewille et al, 2008), and by high content of Ca and P in the diet (Sansom et al, 1983).…”

“…Older animals also have reduced ability to mobilize body reserves of Mg. Lower average environmental temperatures (<14°C) facilitate the onset of the disorder (Mayland, 1988). However, periods of rapid plant growth during any season, resulting in forage of low Mg and high moisture, high nitrogen (N) and K, present dietary conditions that increase the potential for the development of tetany (Robinson et al, 1989). Grass tetany also may develop if animals graze forage that is high in digestible protein, but low in digestible energy (Mayland, 1988).…”

“…Grass tetany has been investigated extensively, but its complex etiology is not well understood. Large number of factors influences the development of the disease (Robinson et al, 1989). It appears within 2-4 weeks after cattle or sheep have been turned out to rapidly growing pasture.…”