Cattlemen with livestock on grass pastures in April and May should be aware of the possibility of grass tetany. Grass tetany, sometimes called grass staggers, is brought on by low blood magnesium (Mg) levels in the affected animal. Magnesium is one of the macro minerals required by cattle 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.
Lush, rapidly growing forages, especially grass species, tend to be low in magnesium. High soil potassium levels have a negative effect on soil Mg uptake by plants. Many soils in our area tend to be low in magnesium to begin with and under cool, wet conditions that are typical in the spring of the year, rapidly growing grass plants will absorb excess potassium before magnesium. This leads to lower Mg content in those plants. Pastures fertilized with nitrogen in the spring can also be a contributing factor to grass tetany because nitrogen increases grass growth and may limit soil Mg availability. High intake of nitrogen and potassium in the diet with marginal magnesium intake is associated with grass tetany.
There are also factors on the animal side of the equation that increase the risk of grass tetany. A cow's requirement for magnesium increases after calving. Cows with 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 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 like 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 symptoms are detected treatment involves administering supplemental magnesium, either intravenously as a calcium magnesium gluconate solution or as an enema with solution of magnesium chloride dissolved in water. It should be noted that even if an animal recovers from grass tetany, that animal will be more prone to grass tetany in the future.