What causes grass tetany and how do cattle producer prevent the problem?
By: Rory Lewandowski, Ohio State University Extension
Grass growth is starting and one potential problem that can be encountered early in the grazing season by livestock is grass tetany, sometimes called grass staggers. Grass tetany is caused by a low blood magnesium level in the affected animal. Magnesium is one of the macro minerals required by animals and it is involved in crucial metabolic functions such as the transmission of nerve impulses and muscle contraction. About 70% of the total body content of magnesium is stored in bones and teeth and adequate blood levels of magnesium are dependent upon daily magnesium intake.
Cool season grasses and small grains such as wheat and rye grazed in the early spring present the greatest risk for grass tetany problems. These forages are most often low in magnesium and calcium and high in potassium. During the early spring when soils are cool and if soil potassium levels are high, these species will take up potassium more readily than magnesium, sometimes termed luxury consumption of potassium. High plant nitrogen levels following a fertilizer application in the spring can also limit magnesium availability. The chapter on grass tetany in the Beef Cattle Handbook says that there is a relationship between potassium (K), calcium (Ca), magnesium (Mg) and nitrogen (N). If the ratio of K: Ca + Mg is greater than 2.2 in forage then that forage is termed tetany prone. Vegetative small grains can commonly have K concentrations of 3 to 5 percent with low levels of Ca and Mg that result in a ratio greater than 2.2. A high dietary intake of nitrogen has also been associated with the development of grass tetany. The highest risk grass and small grain pastures for grazing livestock are those that have high soil potassium levels and/or have been recently fertilized with nitrogen or potassium. Legume or legume/grass pastures offer a much lower risk of grass tetany because they contain higher levels of calcium and magnesium.
All livestock are not at equal risk to develop grass tetany. A cow's requirement for magnesium increases after calving. Cows nursing calves that are under 4 months of age are at greatest risk for grass tetany when they are grazing lush, rapidly growing grass pastures. Steers, heifers, dry cows and lactating cows with calves over 4 months in age are all at lower risk for grass tetany. In general, mature animals are more at risk than young animals because mature animals are not able to mobilize Mg from bones as readily as a young animal when blood Mg levels drop.
The first signs of grass tetany in the animal are restlessness, nervousness and flighty behavior. There may be twitching of the skin and muscles that progress to muscle spasms and convulsions. The affected animal may exhibit loss of coordination and stagger around. Eventually the animal will collapse, lie on her side and paddle with her front legs. Death occurs as a result of respiratory failure during a seizure. Although the symptoms are known, many cattle owners find a dead animal before observing symptoms because the interval between the first symptoms and death can be as short as 4 to 8 hours. If the animal is found in time, treatment is in the form of a solution of magnesium and calcium administered intravenously.
The best way of dealing with grass tetany is through prevention. High risk animals grazing lush, rapidly growing grass pastures should be provided with supplemental magnesium. Generally this is done in a mineral mix. Free-choice high magnesium mineral should contain 12 to 15% magnesium from magnesium oxide. Cattle need to consume four ounces of the mineral supplement daily. Magnesium oxide is unpalatable, which can result in low mineral intake. To help encourage intake, it can be mixed with grain or a flavoring agent like molasses. Generally, this high magnesium mineral mix can be started one to two weeks before the early spring grazing period and continue through late spring when forages are more mature and temperatures are consistently warmer.