Salt solves tetany problems in short term, but phosphorous still needed to address long-term soil needs

LINNEUS, Mo. – Cow chemistry keeps revealing secrets as Dale Blevins delves deeper into the causes of grass tetany, a nutritional disorder than kills cows.

Blevins, a University of Missouri plant scientist, studies the makeup of grass that the afflicted cows eat. He’s making progress.

Sodium – most people know it as common salt – can save the lives of cows that eat lush springtime grass that is short in magnesium and calcium. Lack of those nutrients makes highly productive milk cows vulnerable to tetany.

“Feed salt, lots of loose salt, to cows in spring,” Blevins told field day visitors at the MU Forage Systems Research Center (FSRC), Aug. 3.

Grass tetany has fascinated Blevins since he was a boy on his father’s farm near Ozark, Mo. “It was always one of our best beef cows that lay down and died,” he said.

The disease hits both dairy and beef cows, especially in a cool spring when grass growth is rapid. That’s when a cow’s demand for nutrients to produce milk is high.

Scientific literature historically indicates tetany is associated with calcium and magnesium uptake. In earlier research, Blevins discovered and published results that showed soil phosphorus controlled the grass uptake of those two vital elements.

Grass tetany in cattle is less likely from soil high in phosphorus, but Ozark soil, where Blevins grew up, are notoriously low in phosphorous. For example, soil tests at the MU Southwest Research Center, Mount Vernon, Mo., showed only seven pounds of phosphorus in soil that needed 40 pounds of phosphorus.

Adding small amounts of phosphorus fertilizer boosted hay yields by 1,500 pounds per acre and increased calf weaning weights by 50 pounds. “Those are good reasons to keep phosphorus levels up to soil-test recommendations,” Blevins said. “I believe in soil tests.”

After beef cows died at MU FSRC in the spring of 2007 right after an Easter freeze, Blevins studied grass samples from pastures there that showed the grass lacked sodium, even though the soil was high in phosphorus. This was an unexpected turn of events. Now it was obvious that sodium had something to do with the mystery of tetany.

That’s when Blevins learned that inside the cow sodium helps pump the needed magnesium through the cow’s cell walls.

At least until he learns more, Blevins recommends adding more loose salt for the cow herd to lick to help stave off tetany.

“Spread it out so every cow gets some,” Blevins said. “Don’t put out one salt block that an old bossy cow can dominate. Make sure all the cows get plenty of salt in the spring.”

Blevins has not satisfied his curiosity on the mysteries of grass tetany. As with any advance in discoveries, the solving of one problem usually raises new questions to be answered.