John D. Byrd, Mississippi State University, Bugwood.org
I was called to a farm this week because of six dead cows. It was a sad sight especially since it could have been avoided. The cause was hypomagnesmia (low magnesium) which is more commonly known as Grass Tetany. In this situation, the conditions that increase the risk of grass tetany aligned perfectly (see below).
Grazing animals have low magnesium levels in their blood because the grass they are grazing contains low magnesium. It occurs almost exclusively in grass and not legumes.