While early grazing on cool-season grasses in the spring increases the potential for grass tetany in livestock, particularly in cows still nursing calves less than four months old, producers who supplement their livestock with magnesium could help prevent the potentially fatal disorder from occurring, according to a forage expert from The Ohio State University. 

Grass tetany is a nutritional disorder in livestock caused by low blood magnesium levels, said Rory Lewandowski, agriculture and natural resources educator for the college’s outreach arm, Ohio State University Extension. While the disorder can be treated if caught very early, the best way to deal with grass tetany is to prevent it from occurring at all, he said.

Grass tetany could be prevented by feeding animals that graze in lush, rapidly growing grass pastures a high magnesium mineral mix starting at least a week or two before spring grazing and continuing throughout the spring grazing period, he said.

“Now is the time to start thinking about grass tetany and taking steps to prevent it from happening,” Lewandowski said. “Producers who are grazing in areas with cover crops need to also be aware that certain cover crops such as winter wheat and winter rye are considered higher risk forages with regard to grass tetany.

“Grass tetany can come on very quickly, so we just want to remind producers to be aware that it is a potential problem so they won’t run into a worst-case situation and lose an animal.”

A free choice high magnesium mix should contain 12 to 15 percent magnesium from magnesium oxide and can be mixed with a grain or flavoring agent such as molasses to encourage cattle to ingest it, Lewandowski said. The mixture should be fed to cattle daily in 4-ounce portions throughout late spring until the forages are more mature and temperatures are warmer, he said.

Tetany is most likely to be seen in early spring grazing as cool season grasses and small grains such as wheat and rye are most often low in magnesium and calcium and high in potassium, Lewandowski said.

“During the early spring when soils are cooler and if the soil potassium levels are high, these forages take up potassium easier than magnesium, which increases the risk of grass tetany occurring in susceptible animals,” he said.

Signs of grass tetany include muscle twitching in the flank, lack of muscular coordination, cattle grazing away from the herd, irritability, wide-eyed and staring, staggering, collapse, thrashing and coma. Grass tetany can quickly result in death.