What Is Grass Tetany?

Grass tetany is a livestock metabolic disorder linked to nutritional deficiencies.

Grass tetany is a metabolic disorder that occurs in livestock. Other names for this disorder include grass staggers, wheat pasture poisons, hypo-magnesemia and lactation tetany and is most often found in lactating cows. There are several clinical and field symptoms of the disorder and it is possible to prevent and treat.

Symptoms

Clinical symptoms of grass tetany in livestock generally include deficiencies in serum magnesium and serum calcium. Urinary magnesium of less than 20 parts per million is a diagnostic symptom. In mild cases, an animal's milk yield is reduced and it may act nervous. Animals suffering from acute grass tetany may stop grazing suddenly, express discomfort or unusual alertness, may stagger and will have violent and startling reactions to stimulation. Subacute and chronic grass tetany are similar but symptoms are slower to develop and animals suffering from these forms may show appetite loss, dullness and decreased milk production.

Conditions

Grass tetany tends to appear in animals under conditions of nutritional stress. This includes pasture directly after a frost or other low quality pasture, particularly on soils that are low in available magnesium and high in potassium. Tetany is most common during cool, cloudy weather, particularly when warmer weather follows. Rapidly growing grasses like orchard grass, ryegrass, tall fescue and crested wheatgrass hold the greatest threat of grass tetany; legume pastures rarely present problems.

Treatment

Treatment is important and must occur quickly, as cattle down for more than 12 hours rarely recover. Gentle handling is key because producing excitement frequently causes death. Two hundred cubic centimeters of a 50 percent magnesium sulfate solution (epsom salts) injected under the skin will put a high level of magnesium into the blood within 15 minutes.

Prevention

Forage should be analyzed promptly if grass tetany is suspected; forages with less than .2 percent magnesium and more than 3 percent potassium are especially likely to cause tetany. There are several practices that may prevent grass tetany. These include applying magnesium fertilizer and dolomitic limestone to the soil in order to increase the magnesium concentration in plants. Pastures can be dusted with magnesium oxide to increase intake or animals can be fed a magnesium supplement. Pastures can also be divided so that grass tetany hazard pastures are used for steers and dry stock while legume pastures are used for lactating cows.

References

• New Mexico State University Cooperative Extension Service: Controlling Grass Tetany in Livestock
• University of Florida IFAS Extension: Grass Tetany in Cattle

Resources

• Grass Tetany; André Voisin; 1963