Ag notes: The dangers of grass tetany 

Jerry Little, County Extension Agent for Agriculture/Natural Resources

Spring in Kentucky is a great time of warming and greening up, but it’s also a time when livestock producers need to watch out for grass tetany in their cow herds.

Grass tetany is a condition caused by an abnormally low level of magnesium in the blood. Maintenance of normal blood magnesium is completely dependent on absorption of magnesium from the diet. Deficiencies occur most often in beef cows in early lactation grazing on lush pastures high in potassium and nitrogen and low in magnesium and sodium.  Typically grass tetany occurs when cows are grazing small grains like wheat and cool season grasses like fescue and orchardgrass in late winter and early spring. Grass tetany is showing up earlier this year due to our warm temperatures this month. Fast growing spring grass is usually low in sodium and magnesium.

A veterinarian makes a diagnosis based on history, clinical signs and low magnesium levels in the blood or spinal fluid. Animals with grass tetany need immediate veterinarian treatment. Response to treatment depends largely on the length of time between onset of symptoms and when treatment begins.

Producers that want to prevent grass tetany should start supplementing with a mineral high in magnesium at least 30 days prior to calving. Cows require 20 grams of magnesium daily or 4 ounces per day of a 15 percent magnesium mineral mix daily during late winter and early spring. Magnesium supplements are bitter and sometimes cattle refuse to eat it in the mineral mix. Watch the mineral feeder to make sure that the cattle are eating the recommended amount.

For more information on preventing grass tetany contact the Boyle County Extension Office.

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