NDSU Extension Service - Stark & Billings County


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Grass Tetany

Understanding and prevention

Grass tetany is a metabolic disorder associated with lush pastures due to low concentrations of blood magnesium, which results in nerve impulse failure in animals. With adequate moisture and warm temperatures, grasses will begin to grow rapidly. The concern of grass tetany isn’t normally seen until May, but taking steps to prevent it now will be more effective in the long run. What steps are being taken or should be taken to prevent grass tetany? Even though it may seem premature, it is never too early to plan and ensure proper management practices are in place.


For a better understanding of grass tetany and be able to manage its risk, one needs to understand what factors play a role in it. These include:
•Low magnesium (Mg) content of rapidly growing grasses and pastures
•High potassium (K) content of rapidly growing grasses and pastures
•High crude protein content of grasses and pastures
•Bad weather, storms, stress, etc., that cause cattle to be “off feed” for 24-48 hours
•Lactation: losses of Mg and calcium (Ca) in milk
•Various combinations of the above factors resulting in low blood Mg or Ca


The key to prevention is to be proactive. Measures should be taken to minimize risks associated with cows grazing lush pastures If possible, delay turn-out into lush pastures until plants are 4 to 6 inches tall. This will reduce the occurrence of tetany, in addition to giving pastures a little more time to rest. If delayed grazing is not an option, other management tools should be utilized. First, always provide a high magnesium (Mg) mineral supplement or mineral mix containing at least 8-12% Mg. This needs to be provided two to three weeks before turn-out or before tetany is likely to occur.. Another potential tool is to provide hay while cattle are on lush pastures as the dry forages can act as carriers to provide the animals additional Mg and Ca at critical times.


Cattle will exhibit symptoms of grass tetany, but they may not be observed as death may occur relatively rapidly within 4 to 8 hours. An affected animal will exhibit a series of progressive signs. These include grazing away from the herd, irritability, muscle twitching in the flank, wide-eyed and staring, muscular incoordination, staggering, collapse, thrashing, head thrown back, coma, and finally death. Affected animals should be handled calmly, since sudden death can occur if animals are stressed.


There are treatment options for animals, but its effectiveness depends on the clinical stage when administered. If treatment is started one or two hours after clinical signs develop, the results are usually a quick recovery. Treatment is not effective if delayed until the coma stage. Grass tetany can be treated with an intravenous dextrose-based commercial preparation of magnesium and calcium purchased from a local veterinarian.

Remember cattle are more susceptible to grass tetany in the spring, and certain weather conditions increase susceptibility. Consider and implement prevention practices, monitor cattle for signs of grass tetany, and treat as soon as possible according to a protocol developed with a veterinarian.

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