Editor’s note: Thomas Swerczek does not, nor did the article “The Grass Tetany Puzzle” intend to, espouse the elimination of trace mineral supplements in grazing programs. Rather, the point of the article was that salt has been overlooked as a potential prevention and treatment factor in grass tetany. It is a condition that, in the U.S., occurs mostly in eastern areas where cattle have access to cool-season grasses.We apologize if there was a lack of clarity on this point.

Grass tetany goes by many names – grass staggers, milk tetany, wheat pasture poisoning, and barley poisoning, to name a few. Just as varied as its name has been the speculation as to the cause of this condition. Grass tetany affects mature cattle that graze lush forage following the freezing of early-spring pastures or the sudden growth after rainfall following a drought. The condition mostly occurs in the eastern U.S. in areas with cool-season grasses.

Thomas Swerczek, a veterinary pathologist in Kentucky, thinks the answer may be sodium deficiency.

Grass tetany was first described in Britain in 1930, and was associated with magnesium deficiency and a coexisting calcium deficiency, as well as excess potassium in the blood of affected animals. During cool, wet conditions or regrowth after frost or drought, sodium levels in certain forages plummet, while nitrogen and potassium levels spike.

The traditional recommended preventive has been supplemental dietary magnesium, with treatment consisting of oral and/or intravenous magnesium. But, after examining cattle lost in 2001 following spring frosts in the Midwest – and then analyzing the pastures – Swerczek uncovered some clues about the cause and prevention of grass tetany.

“When I came to Kentucky in 1969, the common preventive for grass tetany was to feed more magnesium. But, cattle wouldn’t eat magnesium free-choice due to its bitter taste, so it was mixed with other feed. And, some farmers fed meat and bone meal, which is high in magnesium,” Swerczek says.

Then, the feeding of dicalcium phosphate and inorganic minerals became common. “Animal scientists and nutritionists thought some forages were poor quality and we needed to add minerals for better utilization. But such supplements still didn’t prevent grass tetany syndrome,” he says.

So, producers evolved to supplementing magnesium during the 2-3 weeks of lush spring growth. When that didn’t reduce grass tetany incidence, Swerczek says nutritionists recommended initiating supplementation even earlier – 4-5 weeks before peak pasture growth.

“That didn’t work, either. So they recommended starting in February, before the grass starts growing. By the 1980s, the recommendation was year-round supplementation, to get it into the animals’ bones,” Swerczek explains. The idea was cattle would access the magnesium out of bone storage when blood levels dropped due to sudden pasture changes.