COLUMBIA, Mo. – A University of Missouri Extension beef nutrition specialist counsels farmers to prepare for grass tetany season in March.

Grass tetany can result from a magnesium deficiency in spring calving herds consuming lush forages high in potassium and low in calcium and sodium, said Justin Sexten of the MU Extension Commercial Agriculture Program.

“Cattle suffering from grass tetany will walk with stiff, uncoordinated legs and frequently urinate,” Sexten said. “During advanced stages, cattle will lie down and thrash with paddling motions and convulsions.”

Older cows during early lactation are most susceptible to grass tetany. Cattle grazing on nitrogen-fertilized grass pastures also are more susceptible due to greater forage potassium levels interfering with magnesium uptake.

Livestock with grass tetany need immediate veterinary attention, he said.  “Avoid placing additional stress on affected animals by moving them to a new pasture.”

To prevent grass tetany, Sexten suggests establishing legumes in grass pastures. “Grass pastures with 30-40 percent legumes will provide increased forage magnesium and calcium while reducing nitrogen fertilizer needs,” he said.

Producers unable to establish pasture legumes should consider supplemental magnesium. Magnesium oxide is the most common source of supplemental magnesium.

“Unfortunately, magnesium oxide is unpalatable, causing difficulty maintaining consistent magnesium intake,” Sexten said. To improve palatability, he recommends mixing magnesium oxide with salt and a carbohydrate source such as ground corn, dried molasses, cottonseed or alfalfa meal in a 1:1:1 ratio.

“Daily supplementation during early spring forage growth is critical to prevention,” he said. “As the winter feeding period ends, producers must remember to consider grass tetany as a critical component to spring pasture management.”

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