What is in this article?:
- Research by a veterinary pathologist indicates salt is a big factor in preventing and treating grass tetany.
- Without adequate sodium in the blood, the body grabs onto the most available cation, which would be magnesium, followed by calcium.
- When the cow consumes frost-damaged forage and the spike of nitrate occurs, her body accesses magnesium in the blood to eliminate the nitrate. This depletes the body and the cow goes down.
“British scientists in the 1930s noticed salt could prevent grass tetany, but no one put it all together. Grass tetany should be called nitrate toxicity/salt deficiency leading to hypomagnesia/hypocalcemia,” Swerczek says.
As grass tetany tends to occur in the eastern half of the U.S., due to the predominance of cool-season grasses, Swerczek contacted Dale Blevins, a professor of plant science at the University of Missouri, to discuss his theory.
Blevins says he first became aware of sodium’s role in grass tetany during a cow/calf/tetany study performed with graduate student T. Ryan Lock. Lock published two refereed journal articles on phosphorus/magnesium/tetany in 2004 in the journal Forage and Grazinglands as a result of his study. During his thorough review of the literature, Blevins says Lock also found several refereed journal articles from England/New Zealand, many on lactating ewes, where a relationship between sodium and tetany was being studied.
Swerczek encouraged Blevins to research the relationship between adequate sodium in the diet and how it prevents grass tetany. When a catastrophic weather episode occurred in spring 2007, with warm weather followed by frost, Blevins analyzed fast-growing tall fescue to see what changes occurred during frost. He published an article in the February 2011 edition of Plant Management Network linking salt deficiency and grass tetany.
Analysis of the grass revealed that sodium had plummeted, but there was no change in magnesium. Blevins says the outbreak of grass tetany in April 2007 wasn’t due to low dietary magnesium, but impaired magnesium absorption. Since magnesium absorption from the rumen is dependent upon sodium, the sodium deficiency (due to freeze injury and drying of young fescue leaves) could be the most damaging consequence of a spring freeze.
“Blevins confirmed what I’d been telling cattlemen for over 10 years – they should use adequate salt in the diet to help prevent grass tetany,” Swerczek says. Blevins also recommends now that, to reduce the risk of grass tetany following spring frosts and freezes, sodium supplementation should not be overlooked for grazing animals.
Swerczek is convinced that excess potassium and nitrate causes an acute depletion of magnesium and calcium in the blood if there is a deficiency of sodium in the blood. His detailed paper on nitrate toxicity and sodium deficiency is available here.