Extension by Anowar Islam

Grass Tetany: A Forage-Related Animal Disorder
By Anowar Islam, UW Extension Forage Agroecologist

    What is grass tetany? It is a metabolic disorder in animal characterized by low blood magnesium (Mg) levels. Sometimes, it is also called “hypomagnesemic tetany” or “grass staggers.”
    Grass tetany occurs due to inadequate levels of blood serum Mg and can be seen throughout the U.S. and many other parts of the world. Temperatures play a big role in the occurrence of grass tetany, and the risk is much higher during the transition from winter to spring. Temperature rises in the range of 40 to 60 degrees encourage a rapid growth of grasses and also increase the frequency of grass tetany. Although this disorder is common on pure pastures, it can also be found on pastures containing legumes or on grass hays.
    There are several factors that increase the chance of grass tetany occurrence, including: when Mg levels are below 0.20 percent in the forage dry matter; potassium (K) concentrations in the forage are high; nitrogen (N) fertilizers are applied at high rates; and the ratio of K with calcium (Ca) + Mg is above 2.2. There is a negative correlation of Mg availability with other nutrient concentrations, when they appear to present elevated levels in the ruminant digestive tract.
    Symptoms of grass tetany include stiff gait, staggering, twitching muscles and convulsions. Older animals, especially older brood cows nursing calves under two months old, are more susceptible to this disorder because Mg remobilization from their bone is less efficient than younger animals.
    Strategies to avoid grass tetany include direct supplementation of animal with Mg, split application and careful management of K and N fertilizations, Mg fertilization of the forage, supplementing dietary energy and fertilization of forage with sulfur (S). Animals showing early symptoms can be given intravenous injections with Ca-Mg-gluconate solution. However, different animals have different susceptibility to grass tetany, so decisions should be made based on this factor. Also, it is advisable to contact local animal nutritionists before making a decision on an injection.
    Where possible, it is wise to consider holding off cattle grazing pastures in early spring until grasses reach a height of about six inches. Also, feeding cattle with a moderate or higher plane of nutrition and/or legume hay can reduce the incidence of grass tetany.
    Anowar Islam is an assistant professor and the UW Extension Forage Agroecologist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or mislam@uwyo.edu.